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

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

The main subjects of study of F. x. are the structure of atoms (see A volume) and molecules (see Molecule), the nature of chem. 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. High-molecular compounds), thermodynamics (see) and thermal effects of chem. reactions (see. Thermochemistry), surface phenomena (see. Detergents, Surface tension, Wetting), properties of electrolyte solutions (see), electrode processes (see. Electrodes) and electromotive forces, metal corrosion, photochem. and radiation processes (see Photochemical reactions, Electromagnetic radiation). Most theories of F. x. based on the laws of statics, quantum (wave) mechanics and thermodynamics. When studying the problems posed in F. x. Various combinations of experimental methods of physics and chemistry are widely used, the so-called. physical and chemical methods of analysis, the basics of which were developed in 1900-1915.

The most widespread 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 Mossbauer effect (nuclear gamma resonance), radiospectroscopy (see Spectroscopy), spectrophotometry (see) and fluorimetry (see), X-ray structural analysis (see), electron microscopy (see), ulypraccentrifugation (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 his writings. alchemist Kunrat (H. Kuhnrath, 1599), but for a long time the meaning put into this term did not correspond to its true meaning. The problems of physical chemistry, close to their modern understanding, were first formulated by MV 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 MV Lomonosov, there is a science that explains, on the basis of the provisions and experiments of physics, what happens in mixed bodies during chemical. reactions. Systematic teaching of F. x. it was started in 1860 in Kharkov un-those by H. N. Beketov, to-ry for the first time at the natural faculty of this un-that organized the physico-chemical department. Following the Kharkov un-tom, the teaching of F. x. was introduced in Kazan (1874), Yuryevsky (1880) and Moscow (1886) high fur boots. Since 1869 the journal of the Russian Physicochemical Society began to be published. Abroad, the Department of Physical Chemistry was first established in Leipzig in 1887.

Formation of F. x. as an independent scientific discipline associated with atomic-molecular doctrine, 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 at 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 DI Mendeleev in 1869 of the periodic law of chem. elements (see. Periodic table of chemical elements).

The modern idea of \u200b\u200bthe structure of the atom was formed at the beginning

20th century The most important milestones on this path are the experimental discovery of the electron and the establishment of its charge, the creation of quantum theory (see) by M. Plank in 1900, the work of N. Bohr (1913), who assumed the existence of an electron shell in the atom and who created its 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 cut in the future it was possible to explain the nature and direction of chemical. connections, theoretically calculate physical and chemical. constants of the simplest molecules, to 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 H. Helmholtz led to the discovery of the conservation law energy - the so-called. the first beginning, 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 heat content of a system, in 1907 A. Einstein compiled the heat capacity equation for 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 chem. reactions, was laid by the works of G.I. Hess, who established in 1840 the law of constancy of the sums of heat. 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, H. Kirch-hoff formulated a law linking the thermal effect of a reaction with the heat capacities of reactants and reaction products. In 1909-

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

The development of electrochemistry, which deals with the study of 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 A. Volta in 1792-1794. galvanic cell. In 1800 appeared the first works of V. Nicolson and Carlyle (A. Kag-leil) 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, linking the output of electrochem. reactions with the amount of electricity and chemical. equivalents of substances. In 1853-1859. Gittorf (J. W. Hittorf) established the relationship between electrochem. the action and mobility of ions, and in 1879 F. W. Kohlrausch discovered the law of independent motion of ions (see) and established a connection between the equivalent electrical conductivity and mobility of cations and anions. In 1875 - 1878. Gibbs (J. VV. Gibbs) and in 1882 G. Helmholtz developed a mathematical model linking the electromotive force of a galvanic cell with the internal energy of chemical. reactions. In 1879, G. Helmholtz created the doctrine of the electric double layer. In 1930-1932. Volmer (M. Vol-mer) and A. N. Frumkin proposed a quantitative theory of electrode processes.

The beginning of the theory of solutions was laid by the works of J. H. Hassenfratz (1798) and J. Gay-Lussac (1819) on the solubility of salts. In 1881-1884 DP Konovalov laid the scientific foundations of the theory and practice of distillation of solutions, and in 1882 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 WF Ph. Pfeffer, and in 1887 J. Van't Hoff created the thermodynamic theory of dilute solutions and derived an equation linking osmotic pressure with the concentration p -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 connecting 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 semipermeable membrane (see. Membrane equilibrium), edges have found wide application in biophysical chemistry (see) and colloidal chemistry (see). In 1923 Debye and E. Huckel developed a statistical theory of strong electrolytes.

The development of the doctrine of the kinetics of chem. reactions, equilibrium and catalysis began with the works of 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 forward and reverse reactions. The concept of "catalysis" was introduced into physical chemistry by I. Berzelius in

1835 Basic principles of teaching

about chem. equilibria were formulated in the writings of Berthollet (C. L. Veg-thollet). The beginning of the dynamic theory of equilibria was laid by the works of Williamson and Clausius, the principle of mobile equilibrium was developed by J. V ant-Hoff, Gibbs and H. Le Chatelier. Berthelot and L. Pean-saint-Gilles established a relationship between the reaction rate and the state of equilibrium. The basic law of chem. kinetics about the proportionality of the reaction rate to the product of active masses (i.e., concentrations) of reactants - 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 valence as the ability of an atom to accept or give electrons, in 1913-1914. L. V. Pisar-zhevsky and S. V. Dain developed the electronic theory of redox reactions (see). In 1903-1905. NA Shilov proposed the theory of coupled reactions, and in 1913 Bodenstein (M. Vo-denstein) discovered chain reactions (see), the theoretical foundations of the course of which were developed in 1926 -1932. H. N. Semenov and Hinshelwood (C. 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 advances have been made in this area, beginning with the artificial fission of atoms and ending with developments in controlled thermonuclear fusion. Among the problems of F. x. it is necessary to highlight the study of the effect on the molecules of gamma radiation (see), the flux of high-energy particles (see Alpha radiation, Iassic 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). Physics and chemistry are developing successfully. mechanics investigating the influence of surface phenomena on the properties of solids.

One of the sections of physical chemistry, 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. the methods allow the study of living cells and tissues in vivo without subjecting them to destruction. Physical and chemical are of no less importance for medicine. theory and presentation. So, the doctrine of the osmotic properties of solutions turned out to be extremely important for understanding water exchange (see. Water-salt metabolism) in humans in health and disease. The creation of the theory of electrolytic dissociation significantly influenced the idea of \u200b\u200bbioelectric phenomena (see) and laid the foundation for 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 the study of acid-base balance (see). To understand the energy of life processes (for example, the functioning of ATP), studies are widely used using chemical methods. thermodynamics. Development of physical and chemical 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 chem. kinetics are the basis for studying the kinetics of biological, primarily enzymatic, processes. An important role in understanding the essence of biol. processes are played by the study of bioluminescence, chemiluminescence (see Biochemiluminescence), the use of luminescent antibodies (see Immunofluorescence), fluorescent ocher (see), etc. to study the properties of tissue and subcellular localization of proteins, nucleic acid, etc. Fiz. .-chem. methods for determining the intensity of the basal metabolism (see) are extremely important in the diagnosis of many diseases, including endocrine diseases.

It should be noted that the study of physical and chemical. properties of biol. 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.

The main research centers in the field of physical chemistry in the USSR are the scientific research institutes of the USSR Academy of Sciences, 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. AE Arbuzova, Ying t of catalysis, Ying t of chemical kinetics and combustion, Ying t of physical chemistry of the Academy of Sciences of the Ukrainian SSR, and others, as well as the corresponding departments in high fur boots.

The main publications that systematically publish articles on physical chemistry are: "Journal of Physical Chemistry", "Kinetics and Catalysis", "Journal of Structural Chemistry", "Radiochemistry", "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.

Physico-chemical methods of analysis, M., 1968; Kireev VA 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, M., 1967; Solo

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

chemistry, Modern problems, 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., from 1903; Journal of Physical Chemistry, Baltimore, from 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 relationship and difference. Therefore, in order to outline the boundaries of physical chemistry with a number of branches of physics and chemistry, it is necessary to consider the relationship and the difference between the chemical and physical forms of motion.

For the chemical form of motion, that is, for a chemical process, a change in the number and arrangement of atoms in the molecule of reacting substances is characteristic. Among the 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 vibration energy in the direction of a certain bond in a 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 a fragile and short-lived complex (the so-called active complex) and the rapidly occurring destruction of this complex into new molecules, since this complex turns out to be unstable during internal vibrations on certain connections.

Thus, an elementary chemical act is a special, critical point of the vibrational 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, that is, many molecules, collisions of molecules and the exchange of energies between them are necessary (transfer of the energy of motion of the molecules of the reaction products to the molecules of the initial substances by means of collisions). 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.

Above are outlined briefly and in the most general outline the mutual relations of the chemical form of motion with two physical forms of motion. Obviously, there are the same connections of the chemical process with the radiation of the motion of the electromagnetic field, with the ionization of atoms and molecules (electrochemistry), etc.

Structure of matter ... This section includes the structure of atoms, the structure of molecules and the theory of aggregate states.

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

In the theory of the structure of molecules, the geometry of molecules, intramolecular motions and forces that bind atoms in a molecule are investigated. In experimental studies of the structure of molecules, the most widely used method is molecular spectroscopy (including radiospectroscopy); 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, as well as the properties of substances in various states of aggregation, are considered. This branch of science, 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, based on the laws of general thermodynamics, the laws of chemical equilibrium and the theory of phase equilibria, which is usually called the phase rule, are presented. Part of chemical thermodynamics is thermochemistry,which considers the thermal effects of chemical reactions.

The theory of solutions aims to explain and predict the properties of solutions (homogeneous mixtures of several substances) based on 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 dissimilar molecules, that is, 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 studied phenomena in the 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, fogs, fumes), the properties of the surface layers become of fundamental importance and determine many peculiar properties of the entire system as a whole. Such microheterogeneoussystems are studied colloidal chemistry,which is a large independent section of physical chemistry and an independent educational discipline in chemical higher educational institutions.

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

Chemical kinetics and catalysis ... 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 do not participate in the stoichiometric reaction equation are studied (catalysis).

Photochemistry. The interaction of radiation and substances participating in chemical transformations (reactions proceeding under the influence of radiation, for example, photographic processes and photosynthesis, luminescence) is investigated. 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 recently emerged areas and smaller sections of this science, which can be considered as parts of larger sections or as independent sections of physical chemistry. Such are, for example, radiation chemistry, physicochemistry of macromolecular substances, magnetochemistry, gas electrochemistry, and other branches of physical chemistry. Some of them are currently growing in importance.

Physical and chemical research methods

The basic methods of physical chemistry are naturally the methods of physics and chemistry. This is primarily 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 course of chemical reactions in time and the laws of chemical equilibrium.

The theoretical comprehension of the experimental material and the creation of a harmonious 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 theory of the structure and properties of individual atoms and molecules and their interaction with each other. The facts concerning 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 information about the properties of individual molecules.

Thermodynamic method , allowing to quantitatively relate different properties of a substance ("macroscopic" properties) and calculate one of these properties based on the experimental values \u200b\u200bof other properties.

Modern physicochemical research in any specific field is characterized by the use of a variety of experimental and theoretical methods to study the various properties of substances and to clarify 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 find out the dependence of the direction, rate and limits of the course of chemical transformations on external conditions and on the structure of molecules - participants in chemical reactions.

Physical chemistry began 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 MV 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, 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 questions that fully meet the above problems and methods. Experimental actions that serve to confirm individual hypotheses and provisions of this concept are also of this nature. MV 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 the confirmation of the law of conservation of matter and force (motion); - in works and experiments related to the theory of solutions - he developed an extensive program of research on this physicochemical phenomenon, which is in the process of development to this day.

This was followed by a break of more than a century, and DI Mendeleev was one of the first physicochemical studies in Russia in the late 1850s.

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

The first department of physical chemistry in Russia was opened in 1914 at the Physics and Mathematics Faculty of St. Petersburg University; in the fall, M.S.Vrevsky, a student of D.P. Konovalov, began reading a compulsory course and practical lessons 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.

Physical chemistry subject

Physical chemistry is the main theoretical foundation of modern chemistry, using theoretical methods of such important branches of physics as quantum mechanics, statistical physics and thermodynamics, nonlinear dynamics, field theory, etc. It includes the theory of the structure of matter, including: about the structure of molecules, chemical thermodynamics, chemical kinetics and catalysis. Electrochemistry, photochemistry, physical chemistry of surface phenomena (including adsorption), radiation chemistry, the theory of metal corrosion, physical chemistry of high-molecular compounds (see physics of polymers), etc. are also distinguished as separate sections in physical chemistry. They are very close to physical chemistry and are sometimes considered as its independent sections of colloidal chemistry, physicochemical analysis and quantum chemistry. Most of the 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.

Difference between physical chemistry and chemical physics

The science that explains chemical phenomena and establishes their laws on the basis of general principles of physics. The name of the science Physical chemistry was introduced by MV Lomonosov, who was the first (1752 1753) who 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 reason for what happens through chem. operations in complex bodies ”. This definition was given to her by the first physicist-chemist MV Lomonosov in a course read ... Great medical encyclopedia

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

Physical chemistry - - a section of chemistry in which the chemical properties of substances are studied based on the physical properties of their constituent atoms and molecules. Modern physical chemistry is a broad interdisciplinary field bordering on various branches of physics ... Encyclopedia of terms, definitions and explanations of building materials

PHYSICAL CHEMISTRY, explains chemical phenomena and establishes their laws on the basis of 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 laws on the basis of 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 ... ... Illustrated Encyclopedic Dictionary

PHYSICAL CHEMISTRY - section chem. science studying chem. 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 chem. kinetics, electrochemistry and colloidal chemistry, teaching ... ... Big Polytechnic Encyclopedia

Sush., Number of synonyms: 1 physical chemistry (1) Dictionary of synonyms ASIS. V.N. Trishin. 2013 ... Synonym dictionary

physical chemistry - - EN physical chemistry A science dealing with the effects of physical phenomena on chemical properties. (Source: LEE) ... ... Technical translator's guide

physical chemistry - - a science that explains chemical phenomena and establishes their laws on the basis of physical principles. Dictionary of Analytical Chemistry ... Chemical terms

Books

  • Physical chemistry, A. V. Artemov. The textbook was created in accordance with the Federal State Educational Standard in the areas of training bachelors, providing for the study of the discipline "Physical Chemistry". ...
  • Physical chemistry, Yu. Ya. Kharitonov. The textbook sets out the basics of physical chemistry in accordance with the approximate program for the discipline "Physical and colloidal chemistry" for the specialty 060301 "Pharmacy". The publication is intended ...

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Khanty-Mansiysk Autonomous Okrug-Yugra

"Soviet professional college"

Basic lecture notes

on the academic discipline: "EN.03 Chemistry"

specialty: "260502 Technology of public catering products"

"Physical and Colloidal Chemistry"

annotation

Compiled by: Ivanova L.V.

Reviewers:

Polyanskaya TV, teacher of natural sciences, FGOU SPO "OKTES";

Chudnovskaya V.G., teacher, chairman of the PUK chemical disciplines.

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

Working with reference lectures 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 consequence, to predictability of the ongoing processes in colloidal and other systems. It helps to professionally develop, using the scientific foundations of physical and colloidal chemistry, approaches to technology for the production, storage and processing of food.

The manual is intended for the organization of classroom and extracurricular work of students in the discipline "EN.03 Chemistry" (Section 1 "Physical Chemistry", Section 3 "Colloidal 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 The first law of thermodynamics

1.1.3 Thermochemistry

1.1.4 The second law of thermodynamics

1.2 Physical states of substances, their characteristics

1.2.1 Characterization of the gaseous state of matter

1.2.2 Characterization 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 Rate of chemical reaction

1.3.2 Catalysis and catalysts

1.3.3 Chemical equilibrium

1.4 Properties of solutions

1.4.1 General characteristics of 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 over solution

1.4.7 Freezing and boiling of 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. Colloidal 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 Methods of obtaining

2.2.2 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 Physicochemical changes in organic matter of food

2.4.1 Proteins, their chemical structure and amino acid composition

2.4.2 Carbohydrates - high molecular weight polysaccharides

2.4.4 Jellies

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.

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

The founder of physical chemistry is M.V. Lomonosov. He was in 1752-1754. the first scientist to give students a course in physical chemistry. The course reading was accompanied by demonstration of experiments and laboratory work. Lomonosov was the first to suggest 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 provide a physical explanation of the essence of chemical processes.

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

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

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

Culinary processes: coagulation of proteins (during 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 are at the heart of environmental protection measures. As a rule, waste water, smoke from factory pipes are also colloidal systems. The methods of destruction of these colloidal systems are based on the laws of physical colloidal chemistry.

Section 1. Physical chemistry

1. 1 The main concepts 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 the 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 crystal of a mineral, 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 the environment)

Open

Closed

Isolated

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 external environment. Heat transfer, mutual transformations of energy, equalization of concentrations can take place inside the system, but the internal energy of the system remains constant.

An open flask of solution from which solvent can evaporate and which can be heated and cooled.

Tightly closed flask with substance.

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

Environmentis everything that is in direct or indirect contact with the system. It is generally accepted that the environment is so large that the return or acquisition of heat 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 parameters areiniya.

If the parameters of the system state 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 - equations of state (for example, the Cliperon-Mendeleev equation for the state of an ideal gas).

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

Thermodynamicallye processs-changes in the system state parameters:

Isothermal (T \u003d const);

Isobaric (P \u003d const);

Isochoric (V \u003d const).

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

Energy consists of the kinetic energy of molecules, including the energy of translational and rotational motion, the energy of the movement 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 function of state. The absolute value of the internal energy cannot be determined, it is only possible to measure the change in the internal energy (U). The change in the internal energy does not depend on the transition path, but depends only on the initial and final state of the system.

Heat (Q)(or the thermal effect of a process) is a quantitative characteristic of the energy that the system receives (gives up) 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 a 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 transfer of energy is realized through the ordered (organized) movement of molecules under the action of a certain force.

1.1. 2 The 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 type to another in strictly equivalent proportions.

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

For a closed system, this law of thermodynamics establishes a connection between the heat received or released by the system in a certain process, the change in the internal energy of the system and the work done at the same time.

In an isolated system, the inner energia is constant, i.e. U \u003d 0.

If heat Q is supplied to a closed system, then this energy is consumedaboutblows to increase the internal energy of the system U and on sifromtopic of work A versus outsidewthe forces of the environment:

In isobaric-isothermal conditions in which living organisms function:

where: p - external pressure,

V - change in the volume of the system.

Substitute (1.2) into (1.1).

Qр \u003d U + рV \u003d (U end - U start) + (рV end - рV start) \u003d (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 that characterizes 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. The chemical reactions and physical-chemical processes may occur with the release and absorption of energy. They are divided into exothermic and endothermic.

The processes in which heat is released are called exothermicand, the processes proceeding with the absorption of heat, - endothermeskye.

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

DH \u003d (H end - H start);

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

ДH \u003d (H end - H start) 0,

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

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 enthalpy of reaction 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 notandsits from the path, along toaboutthe 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, in which the value of the enthalpy (or thermal effect) of the reaction is indicated, is called thermochemical.

Thermochemical equations are used in thermochemistry. Thermochemistry defines standard enthalpy of formation and the transitions from one state to another. The thermochemical equation differs from the chemical one in that the absolute value and sign of the heat effect of the reaction are indicated in the thermochemical equations, which is attributed to one mole of the initial or obtained substance, therefore, stoichiometric coefficients in thermochemical equations can be fractional. In thermochemical equations, the state of aggregation and crystalline form are also noted.

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

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

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

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

1.1. 4 The second law of thermodynamics

This law has the following wording:

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

A spontaneous (natural, spontaneous) transition of energy (in the form of heat) from a less heated body to more heat is impossibleeto that.

The heat of the ocean, for example, can in principle be converted into work (according to the first law of thermodynamics), but only if there is 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 \u003d const), this position is expressed by the following mathematical equation:

H \u003d G + TS or G \u003d H - TS, (1.5)

where H is the heat effect of the reaction observed during its irreversible course;

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

Even with a reversible reaction flow, only part of the heat of the process can go into work. Another part not turned into pandbota, is transmitted from warmer to colder parts of the systemewe.

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

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

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

TS \u003d Q, or S \u003d Q / T, (1.6)

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

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

F \u003d U - TS (for V, T \u003d const) (1.7)

Spontaneous processes can do work. Equilibrium occurs when this opportunity is exhausted. Since negative changes in F and G correspond to spontaneous processes, the sign of the change in function G (at P, T \u003d const) or function F (at V, T \u003d const) will show the possibility or impossibility of spontaneous reaction. If the changes of these functions for the system states 1 and 2 are equal to zero, then the system is in equilibrium.

Entropy differs from other parameters of the state of the system (P, T, V) in that its numerical value and the value of its change cannot be directly measured and can be obtained only indirectly, by calculation. To calculate the S entropy of the reaction aA + bB \u003d cC \u003d 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 \u003d S 0 298K (products) - S 0 298K (reagents), (1.8)

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

4. What is called a thermodynamic process?

5. How is the first law of thermodynamics formulated?

6. What is the ratio of the enthalpy of 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 to determine the fundamental possibility of a particular reaction in the 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 running 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: solid, livedlumpor gaseousThese states are called aggregate statesFor some substances, only two or even one state of aggregation is characteristic. For example, naphthalene and iodine, when heated under normal conditions, pass from solid to gaseous, bypassing the liquid. Substances such as proteins, starch, rubbers, which have huge macromolecules, cannot exist in a gaseous state.

Gases have no constant shape and volume. Liquids have a constant volume but not a constant shape. Solid are characterized by constancy of shape and volume.

1.2. 1 Characteristics of the gaseous state of matter

The following properties are characteristic of gases:

Uniform filling of the entire provided volume;

Low density in comparison with liquid and solid substances and high diffusion rate;

Comparatively easy compressibility.

These properties are determined by the forces of intermolecular attraction and the distance between the 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 great that, in comparison with them, the size of the molecules, and, therefore, the volume of molecules in the total volume of the gas can be neglected. At large distances between molecules are practically no attractive forces between them. Gas in this state is called ideal.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 equation of stateiideal randfor (Cliperon equation-Mendeleev):

where P is the gas pressure,

V - gas volume,

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 the forces of interaction between molecules begin to manifest themselves and it is no longer possible to neglect the intrinsic volume of molecules in comparison with the volume of the body. For a mathematical description of the behavior of real gases, the equation is used Van der Waals:

(p + n 2 a / V 2) (V - nb) \u003d vRT, (2.2)

where a and b are constants,

a / V 2 - correction for mutual attraction,

b - correction for the intrinsic volume of 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 forces of interaction increase so that a substance from a gaseous state can go into a liquid state. For each gas there is a limit critical temperature, above which the gas cannot be converted to liquid under 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.

Figure: 1. Isotherms of real gas

The state of the gas at critical parameters is called critical withaboutstandingIn a critical state, the distinction between liquid and gas disappears, they have the same physical properties.

The transition of gas to liquid can be shown graphically. Figure 1 shows a graphical relationship between volume and pressure at constant temperatures. Such curves are called ofaboutterms.Three areas can be distinguished in isotherms: 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. With increasing temperature, the BC section decreases and turns into an inflection point K, called critical point.

Liquefied gases are widely used in industry. Liquid CO 2 is used for carbonated fruit and mineral water, the preparation of effervescent wines. Liquid SO 2 is used as a disinfectant for the destruction of molds in basements, cellars, wine barrels, fermentation vats. Liquid nitrogen is widely used in medicine and biology to obtain low temperatures during preservation and freezing of blood and biological tissues. Liquid gases are easier to transport.

1.2. 2 Characterization of the liquid state of matter

In contrast to gases, sufficiently large forces of mutual attraction act between liquid molecules, which determines the peculiar character of molecular motion. Thermal motion of a liquid molecule includes oscillatory and translational motion. Each molecule vibrates for some time around a certain equilibrium point, then moves and again takes a new equilibrium position. This determines its fluidity. The forces of intermolecular attraction prevent molecules from moving far apart 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 molecules of the liquid are polar, then two or more molecules are combined (associated) into a complex complex. Such liquids are called associateaboutbathroomsliquids. Associated liquids (water, acetone, alcohols) have higher boiling points, less volatility, 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 a higher temperature than dimethyl ether, which is a non-associated liquid.

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

Surface tension.

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

Figure: 2. The action of intermolecular forces on the interface and inside the liquid

In fig. 2 molecule (a) is inside the liquid, 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 spread.

The molecule (a) is uniformly affected by intermolecular forces from the surrounding molecules, therefore the forces of intermolecular interaction are compensated, the resultant of these forces is zero (f \u003d 0).

The vapor density is much less than the density of the liquid, since the molecules are far from each other at great distances. Therefore, the molecules in the surface layer experience almost no attraction force from these molecules. The resultant of all these forces will be directed into the fluid perpendicular to its surface. Thus, the surface molecules of a liquid are always under the influence of a force that tends to pull them inward and, thereby, reduce the surface of the liquid.

To increase the liquid interface, it is necessary to expend the 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 the uncompensation of intermolecular forces in the surface layer:

q \u003d F / S (F - surface energy) (2.3)

There are many methods for determining surface tension. The most common are the stalagmometric method (drop counting method) 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 a certain ordering of the spatial arrangement of molecules in separate microvolumes. The so-called short-range order is observed near each molecule. At a distance from it at some distance, this pattern is violated. And in the entire volume of the liquid there is no order in the arrangement of particles.

Figure: 3. Stalagmometer Fig. 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.

Instruments called viscometers are used to measure viscosity. The choice of a viscometer and a 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 viscometers are widely used.

1.2. 3 Characterization of the solid state of matter

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

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

Very often, amorphous and crystalline forms are different states of the same substance. So, silicon dioxide is found in nature and 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 an amorphous state to a crystalline one. 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 amorphous (caramelized) states. Over time, the candy can be crystallized, which is undesirable in the confectionery industry. kinetics adsorption dispersed colloidal

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

Questions for self-control:

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

Is it possible to compress real gas infinitely?

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 is the reason for the low compressibility of liquids?

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

How can you explain that surface tension and viscosity decrease with increasing temperature?

By what signs can one distinguish a crystalline body 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 Chemical reaction rate

Kinetics- learning about the speed and mechanism of chemical reactions.

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

The speed of chemical processes can be regulated by changing the conditions of their course. 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 food. All these problems can be solved by applying the laws of chemical kinetics.

Speed \u200b\u200breaction- change in the concentration of reactants 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 the masses, open empirically K.M. Guldberg and P. Waage in 1867.

For the reaction aA + bB \u003d 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, which depends on the nature of the reacting substances and temperature.

The rate of a chemical reaction is proportional to the product of the endnreactions of reactants, taken in powers equal toaboutthe coefficients in the equationtotion.

Reaction rate constantis numerically equal to the reaction rate at the concentration of reactants equal to unity.

Factors affecting the rate of a chemical reaction:

· The nature of the reacting substances;

· Concentration of reactants;

· temperature;

· Pressure (for gases);

· Contact area of \u200b\u200breactants;

· Presence of a catalyst.

With an increase in temperature, the speed of movement of molecules increases, and, consequently, the number of collisions between them per unit time.

The effect of temperature on the rate of a chemical reaction obeys the Van't Hoff rule.

When the temperature rises for every 10 degrees, the speed of thebthe number of reactions increases 2-4 times.

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

where is the temperature coefficient of the reaction,

and 0 - the reaction rate at the 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. There are accelerating and decelerating catalysts.

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

Catalytic reactions-reactions proceeding with the participation of catalysts.

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

Inhibitor-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 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 acceleration of the reaction is associated with the fact that enzymes sharply reduce energy barriers along the reaction path. For example, the activation energy for the decomposition reaction of Н 2 О 2 under the action of the iron (II) ion and catalase molecules, respectively, is 42 and 7.1 kJ / mol; for hydrolysis of urea with acid and urease - respectively 103 and 28 kJ / mol.

Enzymes are very specific compared to inorganic catalysts. For example, the amylase in saliva easily and quickly breaks down starch, but does not catalyze the breakdown of sugar. 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. The fact is described when a weak woman lifted a passenger car by the bumper and held it while people who came to the rescue released a child who fell under it; a person pursued by an angry animal easily overcomes obstacles that are insurmountable for him in his normal state; in important competitions, athletes lose several kilograms in weight during the period of their 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 unique selectivity, therefore their activity is the highest.

1.3. 3 Chemical equilibrium

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

Chemical equilibrium- the state of the system when the speeds of the forward and reverse reactions become equal.

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

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

The direction of the balance shift is determined le Chat principleeleague.

If an equilibrium system is influenced, then equalethis is shiftingtxia aside, weakening this effect.

For example, an increase in temperature shifts the equilibrium towards the endothermic reaction, an increase in the concentration of starting substances shifts the equilibrium towards the reaction products. 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 influencing the rate of a chemical reaction.

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

6. What are 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 chemical equilibrium shift?

11. Formulate Le Chatelier's principle.

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

1. 4 Properties of solutions

1.4. 1 General characteristics of solutions

Solutions are of great importance in human life and practice. So, the processes of assimilation of food by humans and animals are associated with the transfer of nutrients into solution. All the most important physiological fluids (blood, lymph, etc.) are solutions. Manufactures 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. Every solution consists of solutes and a solvent. Usually, the solvent is considered to be the component that exists in 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 that is in a larger amount is considered the solvent.

In terms of structure, solutions occupy an intermediate position between mechanical mixtures and chemical compounds. They are related to mechanical mixtures by the variability of the composition, and with chemical compounds - by the homogeneity 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 own 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, during dissolution, two processes occur simultaneously in the system: the diffusion of the solute in the volume of the solvent (physical process) and the formation of unstable compounds of variable composition - solvates from the molecules of the solvent and the solute - solvates (chemical process). If the solvent is water, then these compounds are called hydrates.

The formation of solutions is a spontaneous process, proceeding with an increase in the disorder of the system, i.e. with increasing entropy. For example, when a crystal dissolves, the system changes from a completely ordered state to a less ordered one. In this case, with an increase in entropy (AS\u003e 0), the free energy of the system (AG<0).

If a 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 concentrations, which also leads to an increase in entropy, i.e. AS\u003e 0, a 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.

Concentration of solutions- 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 solute (percentage)- shows how many grams of a substance are dissolved in 100 g of solution. It is determined by the formula:

where W is the mass fraction of the solute,

m in - the mass of the solute,

m solution is 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 gas solubility is higher if dissolution is accompanied by its chemical interaction with the solvent, and less if no chemical interaction occurs. For example, in 1 liter of water under normal conditions. 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 dissolves in 1000 g of water, and only 25 g in 100 g of ethyl alcohol. The solubility of gases largely depends on temperature. With increasing temperature, their solubility decreases, and with decreasing, it increases. So at 0 0 C in 100 ml of water 171 cm 3 CO 2 dissolves, at 20 0 C - only 87.8 cm 3. Therefore, long-term boiling can almost completely remove dissolved gases from a liquid, and it is advisable to saturate liquids with gas at low temperatures.

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

C \u003d kp, (4.2)

where C is the concentration of gas in the solution,

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

p is the gas pressure above the solution.

The mass of dissolved gas at a constant temperature is directlyaboutproportional to gas pressure over solutionaboutrum.

Henry's Law is valid only for dilute solutions at low pressures. Gases interacting 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 sparkling 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 onset 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 at the sea surface. When a diver rises quickly from a depth, dissolved nitrogen is released into the blood by bubbles, which clog the blood vessels, which can lead to serious consequences.

The gas solubility decreases when the third component is present in the solution. So, 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 ° C, and 10 times less dissolves in 1 g of a saturated solution of NaCl, therefore, when storing chlorine over liquid, water is replaced with a solution of sodium chloride.

1.4. 3 Mutual solubility of liquids

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

Dissolve in each other in any ratio;

Practically insoluble;

Dissolve limitedly.

The mutual solubility of liquids depends primarily on their chemical structure. Even alchemists noticed that "like dissolves in like", ie polar is usually soluble in polar, and non-polar - in 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 liquids differ from each other in polarity, then they are limitedly soluble in each other. With limited solubility, each of the liquids transforms into the other up to a certain limit, resulting in a two-layer system. For example, as the temperature rises, their mutual solubility usually increases, and at a certain temperature, both liquids are mixed 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 with a decrease in temperature and is called lower critical temperatureatroy.

Some analytical determinations are sometimes made using the critical dissolution temperature.

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

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

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

C 1 / C 2 \u003d k, (4.3)

where С 1 and С 2 - the concentration of the solute in the 1st and 2nd solvents,

...

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