Basic methods of physical chemistry. Physical and colloidal chemistry. Theory of reactivity of chemical compounds

PHYSICAL CHEMISTRY - a branch of chemistry devoted to the study of the relationship between chemical and physical phenomena in nature. Positions and methods F. x. have importance for medicine and biomedical sciences, methods F. x. are used to study life processes both in normal and pathological conditions.

The main subjects of study F. x. are the structure of atoms (see A volume) and molecules (see Molecule), the nature of chemical. bonds, chem. equilibrium (see Chemical equilibrium) and kinetics (see Chemical kinetics, Kinetics of biological processes), catalysis (see), theory of gases (see), liquids and solutions (see), structure and chem. properties of crystals (see) and polymers (see. Macromolecular compounds), thermodynamics (see) and thermal effects chemical. reactions (see Thermochemistry), surface phenomena (see Detergents, Surface tension, Wetting), properties of solutions of electrolytes (see), electrode processes (see Electrodes) and electromotive forces, corrosion of metals, photochemical. and radiation processes (see Photochemical reactions, Electromagnetic radiation). Most of the theories F. x. is based on the laws of statics, quantum (wave) mechanics and thermodynamics. When studying the problems posed in F. x. widely used various combinations of experimental methods of physics and chemistry, the so-called. fiz.-chem. methods of analysis, the foundations of which were developed in 1900-1915.

To the most common physical and chemical methods of the second half of the 20th century. include electron paramagnetic resonance (see), nuclear magnetic resonance (see), mass spectrometry (see), the use of the Mössbauer effect (nuclear gamma resonance), radiospectroscopy (see Spectroscopy), spectrophotometry (see) and fluorimetry (see), X-ray diffraction analysis (see), electron microscopy (see), ultracentrifugation (see), gas and liquid chromatography (see), electrophoresis (see), isoelectric focusing (see), polarography (see), potentiometry (see Potentiometric titration), conductometry (see), osmometry (see Osmotic pressure), ebulliometry (see), etc.

The term "physical chemistry" first appeared in the works of him. alchemist Khunrath (H. Kuhnrath, 1599), however for a long time the meaning attached to this term did not correspond to its true meaning. The tasks of physical chemistry, close to their modern understanding, were first formulated by M. V. Lomonosov in the course “Introduction to true physical chemistry”, which he read in 1752 to students of the St. Petersburg Academy of Sciences: physical chemistry, according to M. V. Lomonosov, there is a science that explains, on the basis of the provisions and experiments of physics, what happens in mixed bodies with chem. reactions. Systematic teaching F. x. It was begun since 1860 in Kharkiv un-those by H. N. Beketov, to-ry for the first time on natural f-those of this un-that organized physical and chemical department. Following Kharkiv un-that teaching F. x. was introduced in Kazan (1874), Yuriev (1880) and Moscow (1886) high fur boots. Since 1869, the journal of the Russian Physical and Chemical Society begins to appear. Department abroad physical chemistry was first established in Leipzig in 1887.

F.'s formation x. as an independent scientific discipline is associated with the atomic and molecular theory, i.e., primarily with the discovery in 1748-1756. M.V. Lomonosov and in 1770-1774. A. Lavoisier of the law of conservation of mass of substances in chemical. reactions. The works of Richter (J. V. Richter, 1791 - 1802), who discovered the law of shares (equivalents), Proust (J. L. Proust, 1808), who discovered the law of constancy of composition, and others contributed to the creation in 1802-1810. J. Dalton of atomic theory and the discovery of the law of multiple ratios, which establishes the laws of formation of chemical. connections. In 1811, A. Avogadro introduced the concept of "molecule", linking the atomic theory of the structure of matter with the laws of ideal gases. The logical conclusion of the formation of atomistic views on the nature of matter was the discovery by D. I. Mendeleev in 1869 of the periodic law of chem. elements (see Periodic system chemical elements).

The modern concept of the structure of the atom was formed at the beginning

20th century The most important milestones along this path are the experimental discovery of the electron and the establishment of its charge, the creation of a quantum theory (see) Planck (M. Plank) in 1900, the work of Bohr (N. Bohr, 1913), who suggested the existence of an electron shell in an atom and who created his planetary model, and other studies that served as confirmation of the quantum theory of the structure of the atom. The final stage in the formation of modern ideas about the structure of the atom was the development of quantum (wave) mechanics, with the help of methods a swarm subsequently managed to explain the nature and direction of chemical. connections, theoretically calculate physical.-chemical. constants of the simplest molecules, develop the theory of intermolecular forces, etc.

The initial development of chem. thermodynamics, which studies the laws of mutual transformations of various forms of energy in equilibrium systems, is associated with the research of S. Carnot in 1824. Further work by R. Mayer, J. Joule and G. Helmholtz led to the discovery of the conservation law energy, so-called the first law, or the first law of thermodynamics. The introduction by R. Clausius in 1865 of the concept of "entropy" as a measure of free energy led to the development of the second law of thermodynamics. The third fundamental law of thermodynamics was derived from the Nernst thermal theorem on the asymptotic convergence of the free energy and the heat content of the system, in 1907 A. Einstein compiled the equation for the heat capacity of simple harmonic oscillators, and in

1911 Planck concluded that the entropy of pure substances at absolute zero is zero.

The beginning of the independent existence of thermochemistry - the science of thermal effects of chemical. reactions, was laid down by the works of G. I. Hess, who established in 1840 the law of constancy of heat sums. Of great importance for the development of thermochemistry were the works of Berthelot (R. E. M. Berthelot), to-ry developed calorimetric methods of analysis (see Calorimetry) and discovered the principle of maximum work. In 1859, Kirchhoff (H. Kirch-hoff) formulated a law relating the thermal effect of a reaction to the heat capacities of the reactants and reaction products. In 1909-

1912 Nernst (W. H. Nernst), Einstein and Debye (P. Debye) developed the theory of quantum heat capacity.

The development of electrochemistry, which studies the relationship between chemical and electrical phenomena and the study of the effect of electric current on various substances in solutions, is associated with the creation of Volta (A. Volta) in 1792-1794. galvanic element. In 1800, the first works of V. Nicolson and Carlyle (A. Kag-leil) appeared on the decomposition of water, and in 1803-1807. works of I. Berzelius and W. Hisinger about electrolysis (see) solutions of salts. In 1833-1834. Faraday (M. Faraday) formulated the basic laws of electrolysis, relating the yield of electrochemical. reactions with the amount of electricity and chemical. substance equivalents. In 1853-1859. Hittorf (J. W. Hittorf) established the relationship between the electrochemical. action and mobility of ions, and in 1879 F. W. Kohlrausch opened the law of the independent movement of ions (see) and established connection between equivalent electric conductivity and mobility of cations and anions. In 1875 - 1878. Gibbs (J. VV. Gibbs) and in 1882 G. Helmholtz developed a mathematical model that connects the electromotive force of a galvanic cell with the internal energy of a chemical. reactions. In 1879, G. Helmholtz created the doctrine of a double electric layer. In 1930-1932. Volmer (M. Vol-mer) and A. N. Frumkin proposed a quantitative theory of electrode processes.

The beginning of the study of solutions was laid by the works of Gassenfratz (J. H. Hassenfratz, 1798) and J. Gay-Lussac (1819) on the solubility of salts. In 1881 -1884. D. P. Konovalov laid the scientific foundations for the theory and practice of distillation solutions, and in 1882 Raul (F. M. Raoult) discovered the law of lowering the freezing point of solutions (see Cryometry). The first quantitative measurements of osmotic pressure (see) were made in 1877 by W. F. Ph. Pfeffer, and in 1887 Ya. -ra, its volume and absolute temperature. S. Arrhenius in 1887 formulated the theory of electrolytic dissociation and ionization of salts in solutions (see Electrolytes), and Nernst in 1888 - the osmotic theory. Ostwald (W. Ostwald) discovered regularities relating the degree of dissociation of the electrolyte with its concentration. In 1911, Donnan (F. G. Don-pap) created a theory of the distribution of electrolytes on both sides of a semi-permeable membrane (see. Membrane equilibrium), which is widely used in biophysical chemistry (see) and colloidal chemistry (see). In 1923, Debye and E. Huckel developed the statistical theory of strong electrolytes.

The development of the doctrine of the kinetics of chem. reactions, equilibrium and catalysis began with the work of Wilhelmy (L. Wil-helmy), who created in 1850 the first quantitative theory of chem. reactions, and Williamson (A. W. Williamson), who presented equilibrium as a state of equality of the rates of direct and reverse reactions. The concept of "catalysis" was introduced into physical chemistry by I. Berzelius in

1835 Basic Principles of Doctrine

about chem. equilibrium were formulated in the works of Berthollet (C. L. Beg-thollet). The beginning of the dynamic theory of equilibria was laid by the works of Williamson and Clausius, the principle of moving equilibrium was developed by J. V ant-Hoff, Gibbs and Le Chatelier (H. Le Chatelier). Berthelot and Pean-saint-Gilles (L. Pean-saint-Gilles) established a relationship between the reaction rate and the state of equilibrium. Basic law of chem. kinetics about the proportionality of the reaction rate to the product of active masses (i.e., concentrations) of reacting substances - the law of mass action - was formulated in 1864-1867. Guldberg (S. M. Guldberg) and Waa-ge (P. Waage). In 1893-1897. A. N. Bach and Engler (K. Engler) created the peroxide theory of slow oxidation (see Peroxides), in 1899-1904. Abegg (R. Abegg) and Bodlender (H. Bodlander) developed the concept of valency as the ability of an atom to accept or give away electrons, in 1913-1914. L. V. Pisarzhevsky and S. V. Dain developed the electronic theory of redox reactions (see). In 1903-1905. N. A. Shilov proposed the theory of conjugated reactions, and in 1913 Bodenstein (M. Vo-denstein) discovered chain reactions (see), the theoretical foundations for the course of which were developed in 1926 -1932. H. N. Semenov and Hinshelvud (S. N. Hinsheiwood).

The phenomenon of radioactive decay of atoms (radioactivity) was discovered in 1896 by A. Becquerel. Since then, much attention has been paid to the study of radioactivity (see) and significant progress has been made in this area, starting with the artificial fission of atoms and ending with developments in controlled thermonuclear fusion. Among problems F. x. it is necessary to highlight the study of the effect on molecules of gamma radiation (see), the flow of high-energy particles (see Alpha radiation, Yass-mic radiation, Neutron radiation, Lroton radiation), laser radiation (see Laser), as well as the study of reactions in electrical discharges and low-temperature plasma (plasma chemistry). Physical-chem. is successfully developing. mechanics, investigating the influence of surface phenomena on the properties of solids.

One of the sections of F. x. - photochemistry (see), studies the reactions that occur when a substance absorbs light energy from an external source of radiation.

In F. x. there is no such section, to-ry would not matter for medico-biol. disciplines and ultimately for practical medicine (see Biophysical chemistry). Phys.-chem. methods make it possible to study a living cell and tissues in vivo without exposing them to destruction. Equally important for medicine are physical. theories and ideas. So, the doctrine of the osmotic properties of solutions turned out to be extremely important for understanding water metabolism (see Water-salt metabolism) in humans in normal and pathological conditions. The creation of the theory of electrolytic dissociation significantly influenced the idea of ​​bioelectric phenomena (see) and marked the beginning of the ionic theory of excitation (see) and inhibition (see). The theory of acids and bases (see) made it possible to explain the constancy of the internal environment of the body and served as the basis for studying acid-base balance (see). To understand the energy of life processes (eg, the functioning of ATP), studies are widely used using chemical methods. thermodynamics. Development fiz.-chem. ideas about surface processes (surface tension, wetting, etc.) is essential for understanding the reactions of cellular immunity (see), spreading of cells on non-cellular surfaces, adhesion, etc. Theory and methods of chemical. kinetics are the basis for studying the kinetics of biological, primarily enzymatic, processes. A big role in understanding of essence biol. processes are played by the study of bioluminescence, chemiluminescence (see Biochemiluminescence), the use of luminescent antibodies (see Immunofluorescence), fluorescent ohroms (see), etc. to study the properties of tissue and subcellular localization of proteins, nucleic acids, etc. Physical .-chem. methods for determining the intensity of basal metabolism (see) are extremely important in the diagnosis of many diseases, including endocrine.

It should be noted that the study of physical. biol properties. systems and processes occurring in a living organism, makes it possible to look deeper into the essence and reveal the specifics of living matter and these phenomena.

Main research centers in the field of physical chemistry in the USSR are research institutes of the Academy of Sciences of the USSR, its branches and departments, the Academy of Sciences of the Union Republics: Physico-Chemical Institute im. L. Ya. Karpova, Institute of Physical Chemistry, Institute of Chemical Physics, Institute of New Chemical Problems, Institute of Organic and Physical Chemistry im. A. E. Arbuzova, Institute of Catalysis, Institute of Chemical Kinetics and Combustion, Institute of Physical Chemistry of the Academy of Sciences of the Ukrainian SSR, etc., as well as the corresponding departments in high fur boots.

The main press organs that systematically publish articles on physical chemistry are: the Journal of Physical Chemistry, Kinetics and Catalysis, the Journal of Structural Chemistry, Radiochemistry, and Electrochemistry. Abroad articles on F. x. are published in "Zeitschrift fiir physi-kalische Chemie", "Journal of Physical Chemistry", "Journal de chimie physique et de physico-chimie bio-logique".

Bibliography: Babko A. K. and others.

Physical and chemical methods of analysis, M., 1968; Kireev V. A. Course of physical chemistry, M., 1975; Melvin Hughes

E. A. Physical chemistry, trans. from English, vol. 1 - 2, M., 1962; Nikolaev L. A. Physical chemistry, M., 1972; Development

Physical Chemistry in the USSR, ed. Ya. I. Gerasimova. Moscow, 1967. Solo

viev Yu. I. Essays on the history of physical chemistry, M., 1964; Physical

chemistry, Contemporary Issues, ed. Ya. M. Kolotyrkina, M., 1980.

Periodicals - Journal of Structural Chemistry, M., since 1960; Journal of Physical Chemistry, M., since 1930; Kinetics and catalysis, M., since 1960; Radiochemistry, M.-L., since 1959; Electrochemistry, M., since 1965; Journal de chimie physique et de physico-chimie biologique, P., since 1903; Journal of Physical Chemistry, Baltimore, since 1896; Zeitschrift fiir physikalische Chemie, Lpz., from 1887.

The classification of sciences is based on the classification of the forms of motion of matter and their interrelation and difference. Therefore, in order to outline the boundaries of physical chemistry with a number of branches of physics and chemistry, one should consider the connection and difference between the chemical and physical forms of motion.

For the chemical form of motion, i.e., for a chemical process, a change in the number and arrangement of atoms in the molecule of the reacting substances is characteristic. Among many physical forms of movement (electromagnetic field, movement and transformations of elementary particles, physics of atomic nuclei, etc.) has a particularly close connection with chemical processes intramolecular form of movement (vibrations in a molecule, its electronic excitation and ionization). The simplest chemical process - an elementary act of thermal dissociation of a molecule takes place with an increase in the intensity (amplitude and energy) of vibrations in a molecule, especially vibrations of nuclei along the valence bond between them. Achieving a known critical value of the energy of vibrations in the direction of a certain bond in the molecule leads to the breaking of this bond and the dissociation of the molecule into two parts.

More complex reactions involving several (usually two) molecules can be considered as a combination of two molecules when they collide into an unstable and short-lived complex (the so-called active complex) and the rapid destruction of this complex into new molecules, since this complex turns out to be unstable during internal vibrations. through certain connections.

Thus, an elementary chemical act is a special, critical point of the oscillatory motion of molecules. The latter in itself cannot be considered a chemical movement, but it is the basis for primary chemical processes.

For the chemical transformation of significant masses of matter, i.e., many molecules, the collision of molecules and the exchange of energies between them (the transfer of the energy of the movement of molecules of the reaction products to the molecules of the initial substances by means of collisions) are necessary. Thus, the real chemical process is closely related to the second physical form of movement - chaotic motion of molecules of macroscopic bodies, which is often called thermal motion.

The reciprocal relations of the chemical form of motion with the two physical forms of motion have been outlined above briefly and in the most general terms. Obviously, there are the same connections between the chemical process and the radiation of motion. electromagnetic field, with ionization of atoms and molecules (electrochemistry), etc.

The structure of matter . This section includes the structure of atoms, the structure of molecules and the doctrine of states of aggregation.

The doctrine of the structure of atoms has more to do with physics than with physical chemistry. This doctrine is the basis for studying the structure of molecules.

In the study of the structure of molecules, the geometry of molecules, intramolecular movements and forces that bind atoms in a molecule are studied. In experimental studies of the structure of molecules, the method of molecular spectroscopy (including radio spectroscopy) has received the greatest use; electrical, X-ray, magnetic, and other methods are also widely used.

In the theory of aggregate states, interactions of molecules in gases, liquids, and crystals are considered, as well as the properties of substances in various aggregate states. This branch of science, which is very important for physical chemistry, can be considered a part of physics (molecular physics).

The entire section on the structure of matter can also be considered as part of physics.

Chemical thermodynamics . In this section, on the basis of the laws of general thermodynamics, the laws of chemical equilibrium and the doctrine of phase equilibria, which is usually called the rule of phases, are expounded. Part of chemical thermodynamics is thermochemistry, in which thermal effects are considered chemical reactions.

The doctrine of solutions aims to explain and predict the properties of solutions (homogeneous mixtures of several substances) on the basis of the properties of the substances that make up the solution.

The solution of this problem requires the construction of a general theory of the interaction of heterogeneous molecules, i.e., the solution of the main problem, molecular physics. For the development of a general theory and particular generalizations, the molecular structure of solutions and their various properties depending on the composition are studied.

The doctrine of surface phenomena . Various properties of surface layers of solids and liquids (interfaces between phases) are studied; one of the main phenomena studied in surface layers is adsorption(accumulation of substances in the surface layer).

In systems where the interfaces between liquid, solid and gaseous phases are highly developed (colloidal solutions, emulsions, mists, smokes), the properties of the surface layers become of primary importance and determine many of the unique properties of the entire system as a whole. Such microheterogeneous systems are being studied colloid chemistry, which is a major independent section of physical chemistry and an independent academic discipline in higher chemical educational institutions.

Electrochemistry. The interaction of electrical phenomena and chemical reactions (electrolysis, chemical sources of electric current, the theory of electrosynthesis) is studied. Electrochemistry usually includes the study of the properties of electrolyte solutions, which with equal right can be attributed to the study of solutions.

Chemical kinetics and catalysis . We study the rate of chemical reactions, the dependence of the reaction rate on external conditions (pressure, temperature, electric discharge, etc.), the relationship of the reaction rate with the structure and energy states of molecules, the effect on the reaction rate of substances that are not involved in the stoichiometric reaction equation (catalysis).

Photochemistry. The interaction of radiation and substances involved in chemical transformations (reactions occurring under the influence of radiation, for example, photographic processes and photosynthesis, luminescence) is studied. Photochemistry is closely related to chemical kinetics and the study of the structure of molecules.

The above list of the main sections of physical chemistry does not cover some of the recent areas and smaller sections of this science, which can be considered as parts of larger sections or as independent sections of physical chemistry. Such, for example, are radiation chemistry, the physicochemistry of macromolecular substances, magnetochemistry, gas electrochemistry, and other branches of physical chemistry. Some of them are now rapidly growing in importance.

Methods of physical and chemical research

The basic methods of physical chemistry are naturally the methods of physics and chemistry. This is - first of all, an experimental method - the study of the dependence of the properties of substances on external conditions and the experimental study of the laws of the flow of chemical reactions in time and the laws of chemical equilibrium.

The theoretical understanding of the experimental material and the creation of a coherent system of knowledge of the properties of substances and the laws of chemical reactions is based on the following methods of theoretical physics.

Quantum mechanical method (in particular, the method of wave mechanics), which underlies the study of the structure and properties of individual atoms and molecules and their interaction with each other. Facts relating to the properties of individual molecules are obtained mainly with the help of experimental optical methods.

Statistical physics method , which makes it possible to calculate the properties of a substance; consisting of many molecules (“macroscopic” properties), based on knowledge of the properties of individual molecules.

Thermodynamic method , which allows one to quantitatively relate various properties of a substance (“macroscopic” properties) and calculate some of these properties based on the experimental values ​​of other properties.

Modern physicochemical research in any particular field is characterized by the use of a variety of experimental and theoretical methods to study the various properties of substances and to elucidate their relationship with the structure of molecules. The entire set of data and the above theoretical methods are used to achieve the main goal - to determine the dependence of the direction, speed and limits of chemical transformations on external conditions and on the structure of molecules participating in chemical reactions.

The beginning of physical chemistry was laid in the middle of the 18th century. The term "Physical chemistry", in the modern understanding of the methodology of science and questions of the theory of knowledge, belongs to M. V. Lomonosov, who for the first time read the "Course of True Physical Chemistry" to students of St. Petersburg University. In the preamble to these lectures, he gives the following definition: "Physical chemistry is a science that must, on the basis of the provisions and experiments of physical scientists, explain the reason for what happens through chemical operations in complex bodies." The scientist in the works of his corpuscular-kinetic theory of heat deals with issues that fully meet the above tasks and methods. This is precisely the nature of the experimental actions that serve to confirm individual hypotheses and provisions of this concept. M. V. Lomonosov followed these principles in many areas of his research: in the development and practical implementation of the “science of glass” founded by him, in various experiments devoted to confirming the law of conservation of matter and force (motion); - in works and experiments related to the doctrine of solutions - he developed an extensive program of research on this physical and chemical phenomenon, which is in the process of development to the present day.

This was followed by a break of more than a hundred years, and one of the first physicochemical studies in Russia in the late 1850s was started by D. I. Mendeleev.

The next course in physical chemistry was taught by N. N. Beketov at Kharkov University in 1865.

The first in Russia Department of Physical Chemistry was opened in 1914 at the Faculty of Physics and Mathematics of St. Petersburg University, in the fall, a student of D.P. Konovalov, M.S. Vrevsky, began to read the compulsory course and practical classes in physical chemistry.

The first scientific journal intended to publish articles on physical chemistry was founded in 1887 by W. Ostwald and J. van't Hoff.

The subject of physical chemistry

Physical chemistry is the main theoretical foundation of modern chemistry, using the theoretical methods of such important sections of physics as quantum mechanics, statistical physics and thermodynamics, nonlinear dynamics, field theory, etc. It includes the doctrine of the structure of matter, including: the structure of molecules, chemical thermodynamics, chemical kinetics and catalysis. As separate sections in physical chemistry, electrochemistry, photochemistry, physical chemistry of surface phenomena (including adsorption), radiation chemistry, the study of metal corrosion, physical chemistry of macromolecular compounds (see polymer physics), etc. are also distinguished. Very closely adjacent to physical chemistry and are sometimes considered as its independent sections of colloid chemistry, physico-chemical analysis and quantum chemistry. Most sections of physical chemistry have fairly clear boundaries in terms of objects and methods of research, in terms of methodological features and the apparatus used.

The difference between physical chemistry and chemical physics

The molecularity of an elementary reaction is the number of particles that, according to the experimentally established reaction mechanism, participate in an elementary act of chemical interaction. Monomolecular reactions- reactions in which a chemical transformation of one molecule occurs (isomerization, dissociation, etc.): H 2 S → H 2 + S Bimolecular reactions- reactions, the elementary act of which is carried out when two particles (identical or different) collide: CH 3 Br + KOH → CH 3 OH + KBr Trimolecular reactions- reactions, the elementary act of which is carried out when three particles collide: O 2 + NO + NO → 2NO 2 Reactions with a molecularity greater than three are unknown. For elementary reactions carried out at close concentrations of the starting substances, the values ​​of molecularity and order of the reaction are the same. There is no clearly defined relationship between the concepts of molecularity and reaction order, since the reaction order characterizes the kinetic equation of the reaction, and molecularity characterizes the reaction mechanism. The main areas of chemical thermodynamics are: Classical chemical thermodynamics studying thermodynamic equilibrium in general. Thermochemistry, which studies the thermal effects accompanying chemical reactions. Solution theory, modeling the thermodynamic properties of a substance based on ideas about the molecular structure and data on intermolecular interaction. Chemical thermodynamics is closely related to such branches of chemistry as adsorption and chromatography. Physico-chemical analysis The theory of physicochemical analysis is based on the principles of correspondence and continuity formulated by N. S. Kurnakov. The principle of continuity states that if new phases do not form in the system or existing ones do not disappear, then with a continuous change in the parameters of the system, the properties of individual phases and the properties of the system as a whole change continuously. The correspondence principle states that each complex of phases corresponds to a certain geometric image on the composition-property diagram. Theory of reactivity of chemical compounds High energy chemistry (HVE) studies the chemical reactions and transformations that occur in matter under the influence of nonthermal energy. The mechanisms and kinetics of such reactions and transformations are characterized by substantially nonequilibrium concentrations of fast, excited, or ionized particles with an energy greater than the energy of their thermal motion and, in some cases, chemical bonding. Carriers of non-thermal energy acting on matter: accelerated electrons and ions, fast and slow neutrons, alpha and beta particles, positrons, muons, pions, atoms and molecules at supersonic speeds, electromagnetic radiation quanta, as well as pulsed electrical, magnetic and acoustic fields. The processes of high-energy chemistry are distinguished by time stages into physical, occurring in a time of femtoseconds or less, during which non-thermal energy is distributed unevenly in the medium and a “hot spot” is formed, physical-chemical, during which disequilibrium and inhomogeneity in the “hot spot” are manifested and, finally, chemical, in which the transformations of matter obey the laws of general chemistry. As a result, such ions and excited states of atoms and molecules are formed at room temperatures that cannot arise due to equilibrium processes. The external manifestation of CHE is the formation of ions and excited states of atoms and molecules at room temperatures, at which these particles cannot arise due to equilibrium processes. NE Ablesimov formulated a relaxation principle for controlling the properties of non-equilibrium physical and chemical systems. In the case when the relaxation times are much longer than the duration of the physical impact, it is possible to control the release of chemical forms, phases and, as a consequence, the properties of substances (materials), using information about the relaxation mechanisms in nonequilibrium condensed systems at the physicochemical stage of relaxation processes (including number and during operation). The main sections of the HVE Plasma chemistry (in gas and condensed phases) and others. laser chemistry The ionizing ability is possessed by electromagnetic radiation (X-rays, γ-radiation, synchrotron radiation) and streams of accelerated particles (electrons, protons, neutrons, helions, heavy ions; fission fragments of heavy nuclei, etc.), the energy of which exceeds the ionization potential of atoms or molecules ( in most cases, lying in the range of 10-15 eV). Within the framework of radiation chemistry, some chemical processes are considered that are impossible using traditional chemical approaches. Ionizing radiation can greatly reduce the temperature of chemical reactions without the use of catalysts and initiators. History of radiation chemistry Radiation chemistry arose after the discovery of x-rays by W. Roentgen in 1895 and radioactivity by A. Becquerel in 1896, who were the first to observe radiation effects in photographic plates. The first works on radiation chemistry were carried out in 1899-1903 by the spouses M.Curie and P.Curie. In subsequent years, the greatest number of studies was devoted to the radiolysis of water and aqueous solutions. nuclear chemistry Main directions of nuclear chemistry: study of nuclear reactions and accompanying physical and chemical processes; chemistry of "new atoms"; search and synthesis of new elements and radionuclides by the reactor method; search for new types of radioactive decay. Electrochemistry Electrochemistry is a branch of chemical science that considers systems and interphase boundaries when an electric current flows through them, processes in conductors, on electrodes (from metals or semiconductors, including graphite) and in ionic conductors (electrolytes) are studied. Electrochemistry investigates processes

The science that explains chemical phenomena and establishes their laws on the basis of general principles physics. The name of the science Physical Chemistry was introduced by M.V. Lomonosov, who for the first time (1752 1753) formulated its subject and tasks and established one ... ... Big Encyclopedic Dictionary

PHYSICAL CHEMISTRY- PHYSICAL CHEMISTRY, “a science that explains, on the basis of provisions and experiments, the physical cause of what happens through chem. operations in complex bodies. This definition was given to her by the first physicochemist M.V. Lomonosov in a course read by ... Big Medical Encyclopedia

PHYSICAL CHEMISTRY, the science that studies the physical changes associated with CHEMICAL REACTIONS, as well as the relationship between physical properties and chemical composition. The main sections of physical chemistry THERMODYNAMICS, dealing with changes in energy in ... ... Scientific and technical encyclopedic dictionary

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PHYSICAL CHEMISTRY, explains chemical phenomena and establishes their laws on the basis of the general principles of physics. Includes chemical thermodynamics, chemical kinetics, the doctrine of catalysis, etc. The term physical chemistry was introduced by M.V. Lomonosov in 1753 ... Modern Encyclopedia

Physical chemistry- PHYSICAL CHEMISTRY, explains chemical phenomena and establishes their patterns based on the general principles of physics. It includes chemical thermodynamics, chemical kinetics, the doctrine of catalysis, etc. The term “physical chemistry” was introduced by M.V. Lomonosov in ... ... Illustrated Encyclopedic Dictionary

PHYSICAL CHEMISTRY- section of chem. science, studying chemistry. phenomena based on the principles of physics (see (1)) and physical. experimental methods. F. x. (like chemistry) includes the doctrine of the structure of matter, chem. thermodynamics and chemistry. kinetics, electrochemistry and colloidal chemistry, teaching ... ... Great Polytechnic Encyclopedia

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• Physical Chemistry, A. V. Artemov. The textbook was created in accordance with the Federal State Educational Standard in the areas of training of bachelors, providing for the study of the discipline `Physical Chemistry`.…
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Basic lecture notes

in the academic discipline: "EN.03 Chemistry"

specialty: "260502 Technology of catering products"

"Physical and colloidal chemistry"

annotation

Compiled by: Ivanova L.V.

Reviewers:

Polyanskaya T.V., teacher of natural disciplines, FGOU SPO "OKTES";

Chudnovskaya VG, lecturer, chairman of the PUK of chemical disciplines.

The reference abstract of lectures was compiled in accordance with the requirements of the Federal State Educational Standard (FSES) of secondary vocational education to a minimum of content in the discipline "EN.03 Chemistry" for the training of mid-level specialists: "260807 Technology of public catering products."

Working with the basic lecture notes contributes to the transition from the usual descriptive perception of physical and chemical data to quantitative representations, i.e. leads to a deep and correct understanding of them and, as a result, to the predictability of the processes occurring in colloidal and other systems. This helps to professionally develop, using the scientific foundations of physical and colloidal chemistry, approaches to the technology of obtaining, storing and processing food.

The manual is intended for organizing classroom and extracurricular work of students in the discipline "EN.03 Chemistry" (section 1 "Physical chemistry", section 3 "Colloid chemistry").

Introduction

Section 1. Physical chemistry

1.1 Basic concepts and laws of thermodynamics. Thermochemistry

1.1.1 Basic concepts of thermodynamics

1.1.2 First law of thermodynamics

1.1.3 Thermochemistry

1.1.4 The second law of thermodynamics

1.2 Aggregate states of substances, their characteristics

1.2.1 Characteristics of the gaseous state of matter

1.2.2 Characteristics of the liquid state of matter

1.2.3 Characterization of the solid state of matter

1.3 Chemical kinetics and catalysis. Chemical equilibrium

1.3.1 The rate of a chemical reaction

1.3.2 Catalysis and catalysts

1.3.3 Chemical equilibrium

1.4 Properties of solutions

1.4.1 general characteristics solutions

1.4.2 Solutions of gases in liquids

1.4.3 Mutual solubility of liquids

1.4.4 Solutions of solids in liquids

1.4.5 Diffusion and osmosis in solutions

1.4.6 Saturated vapor pressure of solution

1.4.7 Freezing and boiling solutions

1.4.8 Properties of electrolyte solutions

1.5 Surface phenomena. Adsorption

1.5.1 Adsorption, its types

1.5.2 Adsorption at the solution-gas interface

1.5.3 Ion exchange adsorption

Section 2. Colloid chemistry

2.1 Subject of colloidal chemistry. Disperse systems

2.1.1 General characteristics of dispersed systems

2.1.2 Classification of dispersed systems

2.2 Colloidal solutions

2.2.1 Acquisition methods

2.2.2 The structure of a colloidal particle

2.2.3 Properties of colloidal solutions

2.3 Coarse systems

2.3.2 Suspensions

2.3.3 Emulsions

2.3.4 Aerosols

2.4 Physical and chemical changes organic matter food products

2.4.1 Proteins, their chemical structure and amino acid composition

2.4.2 Carbohydrates - high molecular weight polysaccharides

2.4.4 Jelly

Bibliographic list

Introduction

Physical chemistry is a science that studies the relationship between the chemical and physical properties of substances, chemical and physical phenomena and processes.

Only on the basis of the laws of physical chemistry can such common processes in various branches of the food industry as evaporation, crystallization, drying, sublimation, separation, distillation, extraction and dissolution be understood and implemented. Without knowledge of the methods of physical chemistry, technological control of food production is impossible: determination of moisture, acidity, content of sugars, proteins, fats, vitamins, etc.

The founder of physical chemistry is M.V. Lomonosov. He in 1752-1754. He was the first scientist to give students a course in physical chemistry. The reading of the course was accompanied by a demonstration of experiments and laboratory work. Lomonosov was the first to propose the term "physical chemistry" and gave this scientific discipline the following definition: "Physical chemistry is a science that explains, on the basis of the provisions and experiments of physics, what happens in mixed bodies during chemical operations." Thus, M.V. Lomonosov considered physical chemistry as a science designed to give a physical explanation of the essence of chemical processes.

M.V. Lomonosov wrote the world's first textbook on physical chemistry. The discovery by the great scientist of the law of conservation of matter and energy, the doctrine of the existence of absolute zero, the kinetic theory of gases, a number of works on the study of solutions formed the basis of the emerging physical chemistry, contributed to its formation into an independent science. The period of separation into a separate science lasted more than 100 years. The course of physical chemistry during this time was not read by any of the scientists.

One of the branches of physical chemistry, which has become an independent science, is colloidal chemistry.

colloid chemistry is a science that studies the properties of heterogeneous highly dispersed systems and polymer solutions.

Culinary processes: coagulation of proteins (during the heat treatment of meat, fish, eggs, etc.), obtaining stable emulsions (many sauces), foams (whipping cream, proteins, mousses), aging of jellies (hardening of bread, separation of liquid from jelly, jelly, etc.), adsorption (clarification of broths) - refer to colloidal processes. They are at the heart of all food production.

The laws of physical and colloidal chemistry underlie environmental protection measures. Usually, wastewater, factory chimney smoke - also colloidal systems. Methods for the destruction of these colloidal systems are based on the laws of physical colloidal chemistry.

Section 1. Physical chemistry

1. 1 Mainconcepts and laws of thermodynamics. Termaboutchemistry

1.1.1 Basic concepts of thermodynamics

Thermodynamics- a science that studies the general laws of the mutual transformation of energy from one form to another.

Chemical thermodynamics quantifies the thermal effects of various processes, clarifies the fundamental possibility of a spontaneous flow of chemical reactions and the conditions under which chemical reactions can be in a state of equilibrium.

The object of study in thermodynamics is system- a body or a group of bodies, actually or mentally separated from the environment. A system can be called a mineral crystal, a solution of any substance in a container, a gas in a cylinder, etc.

The system is called thermodynamic, if between the bodies that make up it, there can be an exchange of heat, matter, and if the system is described completely by thermodynamic parameters.

Types of systems (depending on the nature of interaction with environment)

open	Closed	Isolated
It exchanges energy and matter with the environment.	It cannot exchange matter with the environment, but it can exchange energy and work with it.	It does not exchange matter and energy with the environment. Heat transfer, mutual transformations of energy, and concentration equalization can occur inside the system, but the internal energy of the system remains constant.
An open flask containing a solution from which the solvent can evaporate and which can be heated and cooled.	A tightly closed flask with a substance.	The reaction taking place in the thermostat.

The system can be homogeneous- consists of one phase (air, crystal, salt) and heterogeneous- consists of several phases (ice-water, water-benzene).

Phase- a part of a heterogeneous system separated by interfaces and characterized by the same physical properties at all its points.

Environment is everything that is in direct or indirect contact with the system. It is generally accepted that the environment has such a large size that the transfer or acquisition of heat by it does not change its temperature.

The state of a thermodynamic system is determined by mass, volume, pressure, composition, heat capacity, and other characteristics, which are called status parametersInia.

If the parameters of the state of the system do not change over time, then such a state is considered equilibrium. In an equilibrium thermodynamic system, the state parameters are interconnected by certain mathematical equations - the equations of state (for example, the Claiperon-Mendeleev equation for the state of an ideal gas).

Parameters that can be directly measured are called main parameters of the state. State parameters that cannot be directly measured (internal energy, enthalpy, entropy, thermodynamic potentials) are considered as functions of the main parameterstditch state.

thermodynamicallyeprocesss-changes in system state parameters:

isothermal (T=const);

· isobaric (Р=const);

Isochoric (V=const).

All bodies in nature, regardless of the state of aggregation, have a certain reserve internal energy.

Energy is made up of the kinetic energy of molecules, including the energy of translational and rotational motion, the energy of motion of atoms into molecules, electrons in atoms, intranuclear energy, the energy of interaction of particles with each other, etc. The kinetic and potential energy of the body itself is not included in the internal energy. Internal energy is a state function. The absolute value of the internal energy cannot be determined, only the change in internal energy (U) can be measured. The change in internal energy does not depend on the transition path, but depends only on the initial and final states of the system.

Heat (Q)(or the thermal effect of the process) is a quantitative characteristic of the energy that the system receives (gives off) from the environment during this process. Heat is a form of energy transfer realized by changing the kinetic energy of the thermal (chaotic) motion of particles (atoms, molecules). If the process is accompanied by the transfer of energy from the environment to the system, it is called endothermic, otherwise - exothermic. Any exothermic reaction in the forward direction becomes endothermic if it goes in the opposite direction, and vice versa.

Work (A), performed by the system, is due to the interaction of the system with the external environment, as a result of which external forces are overcome, i.e. work is one of the forms of energy exchange with the environment and serves as a quantitative characteristic of the transferred energy, and the energy transfer is realized through the ordered (organized) movement of molecules under the action of a certain force.

1.1. 2 First law of thermodynamics

This is a universal law of nature, the law of conservation and transformation of energy, corresponding to the basic position of dialectical materialism about the eternity and indestructibility of motion. This law was first formulated in 1842 by the outstanding German physicist J. Meyer.

Energy does not disappear and does not arise from nothing, but only transforms from one form to another in strictly equivalent ratios.

Depending on the type of system, the first law of thermodynamics has different formulations.

For a closed system, this law of thermodynamics establishes a relationship between the heat received or released by the system in some process, the change in the internal energy of the system, and the work produced in this case.

AT isolated system inner eneRgia is constant, i.e. U=0.

If heat Q is supplied to a closed system, then this energy is dissipatedaboutpouts to increase the internal energy of the system U and on committing siWiththeme of work A versus outsideshthem environmental forces:

Under isobaric-isothermal conditions in which living organisms function:

where: p - external pressure,

V is the change in the volume of the system.

We substitute (1.2) into (1.1).

Qр = U+рV = (U end - U start) + (рV end - рV start) = (U end + рV end) - (U end + рV start) (1.3)

The sum of the internal energy of the system and the product of volume and pressure (U + pV) is called enthalpy (N) - thermodynamic function characterizing the energy state of the system under isobaric-isothermal conditions. In this way:

Enthalpy is the sum of all types of energy concentrated in a given system, including the mechanical energy of particles, which can manifest itself in the form of work during expansion. Chemical reactions and physico-chemical processes can proceed with the release and absorption of energy. They are divided into exothermic and endothermic.

Processes in which heat is released are called exothermicand, processes occurring with the absorption of heat, - endothermiceskim.

In exothermic processes, the enthalpy decreases (H con H start), therefore:

ДH = (H end - H start);

In endothermic processes, the enthalpy increases (H con H start), therefore:

ДH = (H end - H start) 0,

The enthalpy of a system depends on pressure, temperature, and the amount of substance.

Under isobaric-isothermal conditions, the amount of heat that is released or absorbed during a chemical reaction is characterized by a change in enthalpy and is called reaction enthalpy H. The change in the enthalpy of reaction, determined under standard conditions, is called the standard enthalpy of reaction and is denoted H 0.

Enthalpy of reaction, i.e. the thermal effect of the reaction depends only on the nature and state of the initial substances and final products and does not depend onandsieve from the way, by toaboutto which the reaction proceeds.

Standard conditions:

The amount of substance is 1 mol;

pressure 760 mm. rt. Art. or 101.325 kPa;

temperature 298 0 K or 25 0 C.

1.1. 3 Thermochemistry

Chemical the equation, which indicates the value of the enthalpy (or thermal effect) of the reaction, is called thermochemical.

Thermochemical equations are used in thermochemistry. Thermochemistry determines the thermal effects of a chemical reaction and transitions from one state to another. The thermochemical equation differs from the chemical one in that the thermochemical equations indicate the absolute value and the sign of the thermal effect of the reaction, which is related to one mole of the starting or obtained substance, therefore, the stoichiometric coefficients in thermochemical equations can be fractional. In thermochemical equations, the state of aggregation and the crystalline form are also noted.

The enthalpy of reaction can be determined both experimentally and by calculation using the enthalpies of formation of substances involved in a chemical reaction based on Hess' law(1840):

In thermochemical calculations, the consequences of the Hess law are of great importance:

1 consequence. The enthalpy of the reaction is equal to the difference between the algebraic sum of the enthalpies of formation of products and initial substances, taking into account the stoichiometric coefficients in the reaction equation.

2 consequence. The enthalpy of the direct realization is numerically equal to the enthalpy of the reverse reaction, but with the opposite sign.

1.1. 4 Second law of thermodynamics

This has the following formulations:

The transfer of heat from a cold body to a hot one is associated with compensation, i.e. with the need for additional work, which ultimately turns into heat absorbed by a hot body (for example, in a home refrigerator, heat is transferred from objects to parts of the device, and then to air. This transfer requires the expenditure of electricity). The processes, the implementation of which is associated with compensation, are called irreversibleandmy.

Spontaneous (natural, spontaneous) transition of energy (in the form of heat) from a less heated body to a more heated one is impossible.eto that.

The heat of the ocean, for example, can in principle be converted into work (according to the first law of thermodynamics), but only in the presence of an appropriate refrigerator (according to the second law of thermodynamics).

It is impossible to create a perpetual motion machine of the 2nd kind.

With regard to chemical reactions (at P, T=const), this position is expressed by the following mathematical equation:

H = G + TS or G = H - TS, (1.5)

where H is the thermal effect of the reaction observed during its irreversible flow;

G - change Gibbs free energy(free energy at constant pressure), or a change in the isobaric-isothermal potential, that is, this is the maximum part of the energy of the system that, under given conditions, can turn into useful work. At G 0 the reaction proceeds spontaneously.

Even with a reversible flow of the reaction, only part of the heat of the process can go into work. The other part, not converted into pabot, is transmitted at the same time from more heated to colder parts of the systemewe.

The function S introduced into equation (1.5) is called enteraboutFDI.

Entropy is a function of each specific, stationary state and does not depend on the path to reaching a new state (for example, on what intermediate stages the system goes through when moving from state 1 to state 2).

The product TS is the transferred heat (Q), which cannot be converted into work even with a reversible course of the reaction (the value of "bound energy"). This product shows the amount of internal energy lost in the form of heat:

TS = Q, or S = Q/T, (1.6)

The change in the entropy of the system during the reaction, equal to the heat imparted to the system, divided by the absolute temperature at which the system receives (gives off) this heat.

In addition to the thermodynamic potential - the Gibbs free energy G, in thermodynamics, as an auxiliary function for describing processes, another introduced thermodynamic potential is also of great importance - free energy Helmholtz F(free energy at constant volume), or isochoric-isothermal potential:

F = U - TS (for V, T=const) (1.7)

Spontaneous processes can produce work. Equilibrium occurs when this possibility is exhausted. Since negative changes in F and G correspond to spontaneous processes, the sign of the change in function G (at P, T=const) or function F (at V, T=const) will show the possibility or impossibility of a spontaneous reaction. If the changes in these functions for system states 1 and 2 are zero, then the system is in equilibrium.

Entropy differs from other system state parameters (P, T, V) in that its numerical value and the value of its change cannot be directly measured and can only be obtained indirectly, by calculation. To calculate the entropy S of the reaction aA + bB = cC = dD, it is necessary to subtract the sum of the entropies of the substances on the left side of the equation from the sum of the entropies of the substances on the right side of the equation (taking into account the stoichiometric coefficients). So, for standard conditions:

S 0 298K = S 0 298K (products) - S 0 298K (reagents), (1.8)

Only those processes that are associated with an increase in entropy can occur spontaneously in an isolated system, i.e. the system from a less probable state passes into a more probable one and reaches such a macroscopic state, which corresponds to big number microscopic conditions. In other words, processes are spontaneous when the final state can be realized by a large number of microstates and entropy is a measure of the system's striving for equilibrium. Such processes must be accompanied by an increase in entropy.

Questions for self-control:

1. What fundamental questions does chemical thermodynamics solve?

2. What is called a system, a thermodynamic system?

3. What are called state parameters? What are the state options?

4. What is called a thermodynamic process?

5. How is the first law of thermodynamics formulated?

6. What is the ratio of enthalpy to the internal energy of the system?

7. What is the standard enthalpy of formation?

8. How do chemical equations differ from thermochemical ones?

9. What determines the second law of thermodynamics?

10. What do you need to know in order to determine the fundamental possibility of a particular reaction under given conditions?

11. What thermodynamic factors determine the direction of chemical reactions?

12. How do isobaric-isothermal and isochoric-isothermal potentials change in a spontaneously ongoing process?

1. 2 Aggregate states of substances, their characteristics

Depending on external conditions (temperature and pressure), each substance can be in one of three states of aggregation: hard, livingdcom or gaseous.These states are called aggregate states.For some substances, only two or even one state of aggregation is characteristic. For example, naphthalene, iodine, when heated under normal conditions, from a solid state into a gaseous state, bypassing the liquid state. Substances such as proteins, starch, rubbers, which have huge macromolecules, cannot exist in a gaseous state.

Gases do not have a constant shape and constant volume. Liquids have a constant volume but do not have a constant shape. Solids are characterized by constancy of shape and volume.

1.2. 1 Character of the gaseous state of matter

For gases, the following properties are:

Uniform filling of the entire provided volume;

Low density compared to liquid and solid substances and high diffusion rate;

Relatively easy compressibility.

These properties are determined by the forces of intermolecular attraction and the distance between molecules.

In a gas, the molecules are at a very large distance from each other, the forces of attraction between them are negligible. At low pressures, the distances between gas molecules are so large that, compared with them, the size of molecules, and, consequently, the volume of molecules in the total volume of gas, can be neglected. At large distances between molecules, there are practically no forces of attraction between them. A gas in this state is called perfect.Under normal conditions T \u003d 273 0 K (0 0 C) and p \u003d 101.325 kPa, real gases, regardless of nature, can be considered ideal and applied to them the equation isIideal gafor (Claiperon equation-Mendeleev):

where P is the gas pressure,

V is the volume of gas,

The amount of substance

R - universal gas constant (in SI units R \u003d 8.314 J / molK),

T is the absolute temperature.

Real gases at high pressures and low temperatures do not obey the equation of state of an ideal gas, since under these conditions interaction forces between molecules begin to manifest themselves and it is no longer possible to neglect the intrinsic volume of molecules compared to the volume of the body. To mathematically describe the behavior of real gases, the equation is used van der Waals:

(p + n 2 a/V 2) (V - nb) = vRT, (2.2)

where a and b are constants,

a / V 2 - correction for mutual attraction,

b is the correction for the intrinsic volume of the molecules,

n is the number of moles of gas.

With an increase in pressure and a decrease in temperature, the distances between molecules decrease, and the interaction forces increase so that a substance can go from a gaseous state to a liquid one. For every gas there is a limit critical temperature, above which a gas cannot be liquefied at any pressure. The pressure required to liquefy a gas at a critical temperature is called critical pressure, and the volume of one mole of gas under these conditions critical volumeemom.

Rice. 1. Real gas isotherms

The state of the gas at critical parameters is called critical withaboutstanding.In the critical state, the difference between liquid and gas disappears, they have the same physical properties.

The transition of a gas into a liquid can be shown graphically. Figure 1 shows a graphical relationship between volume and pressure at constant temperatures. Such curves are called fromaboutterms. The isotherms can be divided into three sections: AB, BC, CD at low temperatures. AB - corresponds to the gaseous state, BC - corresponds to the transition of gas into liquid, CD - characterizes the liquid state. As the temperature rises, the section BC decreases and turns into an inflection point K, called critical point.

Liquefied gases find a great industrial application. Liquid CO 2 is used for carbonating fruit and mineral waters, making sparkling wines. Liquid SO 2 is used as disinfectant for the destruction of mold fungi in cellars, cellars, wine barrels, fermentation tanks. Liquid nitrogen is widely used in medicine and biology to obtain low temperatures during canning and freezing of blood and biological tissues. Liquid gases are more convenient to transport.

1.2. 2 Characteristics of the liquid state of matter

Unlike gases, rather large forces of mutual attraction act between liquid molecules, which determines the peculiar nature of molecular motion. The thermal motion of a liquid molecule includes oscillatory and translational motions. Each molecule oscillates around a certain equilibrium point for some time, then moves and again occupies a new equilibrium position. This determines its fluidity. The forces of intermolecular attraction do not allow molecules to move far from each other during their movement. The total effect of the attraction of molecules can be represented as the internal pressure of liquids, which reaches very high values. This explains the constancy of volume and the practical incompressibility of liquids, although they easily take any form.

The properties of liquids also depend on the volume of molecules, their shape and polarity. If the liquid molecules are polar, then two or more molecules combine (associate) into a complex complex. Such liquids are called associateaboutbathrooms liquids. Associated liquids (water, acetone, alcohols) have higher boiling points, lower volatility, and higher dielectric constant. For example, ethyl alcohol and dimethyl ether have the same molecular formula (C 2 H 6 O). Alcohol is an associated liquid and boils at more high temperature than dimethyl ether, which is a non-associated liquid.

The liquid state is characterized by such physical properties as plotness, viscosity, surface tension.

Surface tension.

The state of the molecules in the surface layer differs significantly from the state of the molecules in the depth of the liquid. Consider a simple case - liquid - vapor (Fig. 2).

Rice. 2. Action of intermolecular forces on the interface and inside the liquid

On fig. 2, the molecule (a) is inside the liquid, the molecule (b) is in the surface layer. The spheres around them are the distances over which the forces of intermolecular attraction of the surrounding molecules extend.

The molecule (a) is uniformly affected by intermolecular forces from the surrounding molecules, so the forces of intermolecular interaction are compensated, the resultant of these forces is equal to zero (f=0).

The density of a vapor is much less than the density of a liquid, since the molecules are far apart from each other. Therefore, the molecules in the surface layer almost do not experience the force of attraction from these molecules. The resultant of all these forces will be directed inside the liquid perpendicular to its surface. Thus, the surface molecules of a liquid are always under the influence of a force that tends to draw them in and, thereby, reduce the surface of the liquid.

To increase the liquid interface, it is necessary to expend work A (J). The work required to increase the interface S by 1 m 2 is a measure of the surface energy or surface tension.

Thus, the surface tension d (J / m 2 \u003d Nm / m 2 \u003d N / m) is the result of uncompensated intermolecular forces in the surface layer:

q = F/S (F - surface energy) (2.3)

There are many methods for determining surface tension. The most common are the stalagmometric method (the method of counting drops) and the method of the highest pressure of gas bubbles.

Using the methods of X-ray diffraction analysis, it was found that in liquids there is some orderliness in the spatial arrangement of molecules in individual microvolumes. Near each molecule, the so-called short-range order is observed. At some distance from it, this regularity is violated. And in the entire volume of the liquid there is no order in the arrangement of particles.

Rice. 3. Stalagmometer 4. Viscometer

Viscosity h (Pa s) - the property to resist the movement of one part of the liquid relative to the other. In practical life, a person is faced with a large variety of liquid systems, the viscosity of which is different - water, milk, vegetable oils, sour cream, honey, juices, molasses, etc.

The viscosity of liquids is due to intermolecular effects that limit the mobility of molecules. It depends on the nature of the liquid, temperature, pressure.

Viscosity is measured by devices called viscometers. The choice of viscometer and method for determining the viscosity depends on the state of the system under study and its concentration.

For liquids with a low viscosity or low concentration, capillary-type viscometers are widely used.

1.2. 3 Characteristics of the solid state of matter

Solids, unlike liquids and gases, retain their shape. The attractive forces between the particles that make up a solid body are so great that they cannot move freely relative to each other, but only oscillate around some middle position.

All solids are divided into crystalline and amorphous.In crystalline bodies, the particles are arranged in a certain order characteristic of each substance, and this order extends to the entire volume. Throughout the volume of an amorphous body, there is no order in the arrangement of particles. In this respect, amorphous bodies can be considered as liquids with an abnormally high viscosity.

Very often, amorphous and crystalline forms are different states of the same substance. So, silicon dioxide is found in nature both in the form of quartz crystals (rock crystal), and in an amorphous form - the mineral flint. Known crystalline and amorphous carbon.

The crystalline form is the most stable, substances gradually pass from the amorphous state to the crystalline state. Under normal conditions, this process is very slow, an increase in temperature can speed it up. For example, sugar can be in crystalline (granulated sugar, lump sugar) and in amorphous (caramelized) states. Over time, caramel can crystallize, which is undesirable in the confectionery industry. kinetics adsorption dispersed colloidal

The order in the spatial arrangement of particles and crystalline bodies - crystal cell- defines external signs crystalline state. These include: 1) a definite and pronounced melting point; 2) a certain geometric shape of single crystals; 3) anisotropy.

Questions for self-control:

Under what conditions do the properties of a real gas approach those of an ideal gas?

Is it possible to compress a real gas indefinitely?

What is the physical meaning of the constants in the equation of state for a real gas?

Is it possible, knowing the temperature and pressure, to determine the number of molecules per unit volume?

What causes low compressibility of liquids?

How does the formation of a hydrogen bond between molecules affect the properties of a liquid?

How can one explain the decrease in surface tension and viscosity with increasing temperature?

How can a crystalline solid be distinguished from an amorphous one?

What is the main difference in the structure of crystalline and amorphous bodies?

1. 3 Chemical kinetics and catalysis.Chemical equilibrium

1.3.1 The rate of a chemical reaction

Kinetics- the study of the rate and mechanism of chemical reactions.

The question of the rate of a chemical reaction is of great practical and theoretical importance. The course of biochemical processes in the body, physicochemical changes in food products during heat treatment, and the performance of factory equipment depend on the reaction rate.

The speed of chemical processes can be controlled by changing the conditions of their occurrence. In some cases, it is desirable to intensify the process in order to obtain more product per unit of time. Sometimes it is necessary to reduce the rate of a chemical reaction, for example, to slow down the oxidation of fats in foods. All these problems can be solved by applying the laws of chemical kinetics.

Speed ​​reaction- change in the concentration of reacting substances per unit of time.

where c is the change in the concentration of reactants,

t - time interval.

The dependence of high-speed chemical reactions on concentration is determined the law of mass action, open empirical way K.M. Guldberg and P. Waage in 1867.

For the reaction aA + bB = C

where: A and B are the concentrations of reactants,

a and b are the coefficients in the equation,

k - coefficient of proportionality, called the rate constant, depending on the nature of the reactants and temperature.

The rate of a chemical reaction is proportional to the product of the endnfractions of reactants taken in powers equal toaboutcoefficients in the rea equationtotions.

Reaction rate constant numerically equal to the reaction rate at concentrations of reactants equal to unity.

Factors affecting the rate of a chemical reaction:

the nature of the reactants;

the concentration of reactants;

· temperature;

pressure (for gases);

the area of ​​contact of the reactants;

the presence of a catalyst.

As the temperature rises, the speed of movement of molecules increases, and, consequently, the number of collisions between them per unit time.

The influence of temperature on the rate of a chemical reaction obeys the van't Hoff rule.

For every 10 degrees increase in temperature, thebMost of the reactions increase by 2-4 times.

The number showing how many times the rate of a given reaction increases when the temperature rises by 10 degrees is called temperature toaboutreaction factor. Mathematically, this dependence is expressed by the relation:

where is the temperature coefficient of the reaction,

and 0 - reaction rates at initial (t 1) and final (t 2) temperatures;

t - temperature change t 2 - t 1.

Van't Hoff's rule is approximate and can be applied to reactions occurring at temperatures from 0 to 300 degrees and in a small temperature range. As the temperature rises, the temperature coefficient of the reaction rate decreases, approaching unity.

A more accurate dependence of the rate of a chemical reaction on temperature was experimentally established by Arrhenius:

where k is the reaction rate constant,

B and A are constants for this reaction.

1.3. 2 Catalysis and catalysts

Catalyst A substance that changes the rate of a chemical reaction but is not consumed. Catalysts are either accelerating or decelerating.

Catalysis- the phenomenon of changing the reaction rate in the presence of catalysts.

catalytic reactions-reactions proceeding with the participation of catalysts.

If the catalyst is one of the products of the reaction, then the reaction is called autocatalytic, and the phenomenon itself autocatalysis.

Inhibitor a catalyst that slows down the reaction.

An example of positive catalysts is water in the interaction of aluminum powder with iodine.

Enzymes-biological catalysts of protein nature.

Enzymes are present in all living cells. It is customary to divide enzymes into simple and complex, or one-component or two-component. Simple enzymes consist only of protein, complex enzymes consist of protein and a non-protein part, which is called coenzyme.

Enzymes are characterized by high catalytic activity and selectivity. In terms of catalytic activity, they are significantly superior to inorganic catalysts. For example, 1 mole of catalase at 0 degrees decomposes 200,000 moles of H 2 O 2 in one second, and 1 mole of platinum at 20 degrees decomposes from 10 to 80 moles of hydrogen peroxide in one second.

Such accelerations of the reaction are due to the fact that enzymes sharply reduce energy barriers in the reaction path. For example, the activation energy for the decomposition reaction of H 2 O 2 under the action of an iron (II) ion and catalase molecules, respectively, is 42 and 7.1 kJ / mol; for the hydrolysis of urea with acid and urease, respectively, 103 and 28 kJ/mol.

Enzymes are very specific compared to inorganic catalysts. For example, amylase, contained in saliva, easily and quickly breaks down starch, but does not catalyze the process of sugar breakdown. Urease is extremely effective in catalyzing the hydrolysis of urea, but has no effect on its derivatives. This feature of enzymes allows living organisms, having an appropriate set of enzymes, to actively respond to external influences. For example, it has been noticed that in stressful situations our body shows amazing capabilities. A fact is described when a weak woman lifted a car by the bumper and held it while people came to the rescue to free a child who fell under it; a person pursued by an angry animal easily overcomes obstacles that are insurmountable for him in his usual state; in important competitions, athletes lose several kilograms in weight during the period of performance.

All that has been said about the remarkable properties of enzymes is explained by the fact that the selectivity of action (selectivity) and activity are interrelated: the higher the selectivity, the higher its activity. Enzymes have a unique selectivity, and therefore their activity is the highest.

1.3. 3 Chemical equilibrium

Reversible reactions can go in two opposite directions. They do not reach the end, but end with the establishment of chemical equilibrium.

Chemical equilibrium The state of a system when the rates of the forward and reverse reactions become equal.

The state of chemical equilibrium is maintained until conditions change. When external conditions change, the equilibrium is disturbed, and after a while the system will come to a new state of equilibrium.

Balance shift the transition of a system from one state of equilibrium to another.

The direction of equilibrium shift is determined Le Chat principleeleagues.

If the equilibrium system is affected, then it is equal toeyou are shifting thistin the direction that weakens this effect.

For example, an increase in temperature shifts the equilibrium towards an endothermic reaction, an increase in the concentration of the starting substances shifts the equilibrium towards the products of the reaction. Pressure only changes the equilibrium of reactions involving gases. An increase in pressure shifts the equilibrium in the direction of a reaction proceeding with a change in volume.

Questions for Samokontroll:

1. What does kinetics study?

2. What is called the rate of chemical reactions?

3. Why is there a minus sign in the mathematical equation for the rate of a chemical reaction?

4. List the factors that affect the rate of a chemical reaction.

5. Describe the effect of concentration, temperature, nature of reactants on the rate of a chemical reaction.

6. What is called catalysis and catalyst?

7. How are catalytic reactions classified?

8. What are inhibitors?

9. What is called chemical equilibrium?

10. What is called a shift in chemical equilibrium?

11. Formulate Le Chatelier's principle.

12. In which direction will the equilibrium of the equilibrium reaction shift with increasing temperature? Pressure (if gases are involved in the reactions)? The concentration of one of the reactants?

1. 4 Solution properties

1.4. 1 General characteristics of solutions

Solutions are of great importance in human life and practical activities. So, the processes of assimilation of food by humans and animals are associated with the translation nutrients into solution. Solutions are all the most important physiological fluids (blood, lymph, etc.). Industries based on chemical processes are usually associated with the use of solutions.

Solutions- multicomponent homogeneous systems in which one or more substances are distributed in the form of molecules, atoms or ions in the medium of another substance - a solvent.

The solution can have any state of aggregation - solid, liquid or gaseous. Any solution consists of solutes and a solvent. Usually, a solvent is considered to be a component that exists in its pure form in the same state of aggregation as the resulting solution (for example, a solution of salt in water: salt is a solute, water is a solvent). If both components were in the same state of aggregation before dissolution (for example, alcohol and water), then the component in a larger amount is considered the solvent.

In terms of structure, solutions occupy an intermediate position between mechanical mixtures and chemical compounds. With mechanical mixtures, they have in common the variability of composition, and with chemical compounds - the uniformity of the composition throughout the phase and the presence of a thermal effect during formation. In accordance with this, at first there were two opposing theories: "physical" and "chemical", each of which defended its views on the structure of solutions.

Modern ideas about the structure of solutions are based on the solvation theory put forward by Mendeleev and developed by his followers. According to this theory, two processes simultaneously occur in the system during dissolution: the diffusion of the solute in the volume of the solvent (physical process) and the formation of unstable compounds of variable composition - solvates (chemical process) from the molecules of the solvent and the solute. If the solvent is water, then these compounds are called hydrates.

The formation of solutions is a spontaneous process that proceeds with an increase in the disorder of the system, i.e. with an increase in entropy. For example, when a crystal is dissolved, the system goes from a completely ordered state to a less ordered one. In this case, with an increase in entropy (AS > 0), the free energy of the system decreases (AG<0).

If the solution is formed from 2 liquids, then the driving force of the dissolution process is due to the tendency of the components of the solution to equalize the concentrations, which also leads to an increase in entropy, i.e. AS > 0 and AQ< 0. Растворение вещества - процесс обратимый. И как всякий обратный процесс, растворение заканчивается установлением динамического равновесия: нерастворенное вещество - вещество в растворе. Раствор, находящийся в равновесии с растворяющимся веществом, называют насыщенным раствором, а достигнутую предельную концентрацию насыщенного раствора - растворимостью.

The most important characteristic of a solution is its composition or concentration of components.

Solution concentration- the amount of a solute contained in a certain amount of a solution or solvent.

The concentration of solutions can be expressed in different ways. In chemical practice, the following methods of expressing concentrations are most commonly used:

1. Mass fraction of a dissolved substance (percentage concentration)- shows how many grams of a substance are dissolved in 100 g of a solution. It is determined by the formula:

where W is the mass fraction of the solute,

m in-va - the mass of the dissolved substance,

m solution - the mass of the solution.

2. Molar concentration- shows how many moles of a solute are contained in 1 liter of solution.

3. Molar concentration- shows how many moles of a substance are contained in 1 kg of solvent.

1.4. 2 Solutions of gases in liquids

The solubility of gases in liquids depends on their nature, the nature of the solvent, temperature and pressure. As a rule, the solubility of a gas is greater if the dissolution is accompanied by its chemical interaction with the solvent, and less if there is no chemical interaction. For example, in 1 liter of water at n.o. dissolves 0.0002 g of hydrogen, which does not interact with water, and 875 g of ammonia, which reacts with water to form ammonium hydroxide.

The dependence of the solubility of gases on the nature of the solvent can be shown in the following examples. Under the same conditions, 87.5 g of NH 3 is dissolved in 1000 g of water, and only 25 g is dissolved in 100 g of ethyl alcohol. The solubility of gases largely depends on temperature. As the temperature rises, their solubility decreases, and as the temperature decreases, it increases. So at 0 0 C, 171 cm 3 CO 2 dissolves in 100 ml of water, at 20 0 C - only 87.8 cm 3. Therefore, prolonged boiling can almost completely remove dissolved gases from a liquid, and it is advisable to saturate liquids with gas at low temperatures.

The solubility of a gas also depends on pressure. The dependence of gas solubility on pressure is determined ge lawnri.

C = k p, (4.2)

where C is the gas concentration in the solution,

k - coefficient of proportionality, depending on the nature of the liquid and gas,

p is the pressure of the gas above the solution.

The mass of dissolved gas at constant temperature is directly praboutis proportional to the gas pressure over the solutionaboutrum.

Henry's law is valid only for dilute solutions at low pressures. Gases that interact with the solvent NH 3 , SO 2 , HC1 with water do not obey Henry's law. Their solubility also increases with increasing pressure, but according to a more complex law.

The manifestation of Henry's law is illustrated by the formation of copious foam when uncorking a bottle of soda water or a bottle of champagne; here there is a sharp decrease in the solubility of the gas with a decrease in its partial pressure. The same law explains the occurrence of decompression sickness. At a depth of 40 m below sea level, the total pressure is 600 kPa and the solubility of nitrogen in blood plasma is 9 times greater than on the sea surface. When a diver rises rapidly from a depth, dissolved nitrogen is released into the blood in bubbles that clog blood vessels, which can lead to serious consequences.

The solubility of a gas decreases when a third component is present in the solution. Thus, gases dissolve much worse in electrolyte solutions than in pure water. For example, 3 10 3 m 3 of chlorine dissolves in 1 g of water at 0 0 C, and 10 times less dissolves in 1 g of a saturated NaCl solution, therefore, when chlorine is stored above a liquid, water is replaced with a sodium chloride solution.

1.4. 3 Mutual solubility of liquids

Unlike the solubility of gases in liquids, the dissolution of a liquid is a more complex process. When two liquids are mixed, they can:

Dissolve in each other in any ratio;

Practically insoluble;

Dissolve limited.

The mutual solubility of liquids depends primarily on their chemical structure. Even the alchemists noticed that "like dissolves in like", i.e. the polar is usually soluble in the polar, and the non-polar in the non-polar. For this reason, water (polar liquid) is a good solvent for polar liquids (ethyl alcohol, acetic acid, etc.) and does not dissolve non-polar liquids (benzene, kerosene, etc.) at all. If the liquids differ from each other in polarity, then they are limitedly soluble in each other. With limited solubility, each of the liquids passes into the other up to a certain limit, resulting in a two-layer system. For example, with an increase in temperature, their mutual solubility usually increases, and at a certain temperature both liquids mix in any ratio, and the boundary between them disappears. This temperature is called critical.

The critical temperature reached by heating is called upper critical temperature.

Known mixtures of liquids, where the solubility decreases with increasing temperature. Therefore, the critical temperature is reached as the temperature decreases and is called lower critical temperatureatRoy.

Using the critical dissolution temperature, some analytical determinations are sometimes carried out.

Of particular interest is the solubility of various substances in two-layer systems consisting of two insoluble liquids.

If a third substance capable of solubility in each of them is introduced into a system consisting of two immiscible liquids, then the solute will be distributed between both liquids in proportion to its solubility in each of them.

The ratio of the concentrations of a substance distributed between two immiscible liquids at a constant temperature remains constant, regardless of the total amount of solute.

С 1 /С 2 = k, (4.3)

where C 1 and C 2 are the concentration of the solute in the 1st and 2nd solvents,

...

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