Carl Gustav Jung was born in Switzerland on July 26, 1875. Up to 9 years, i.e. up to...
– a sustained chain reaction involving combustion, which is an exothermic reaction in which an oxidizer, usually oxygen, oxidizes a fuel, usually carbon, producing combustion products such as carbon dioxide, water, heat and light. A typical example is methane combustion:
CH 4 + 2 O 2 → CO 2 + 2 H 2 O
The heat generated by combustion can be used to power the combustion itself, and when this is sufficient and no additional energy is required to maintain combustion, a fire occurs. To stop a fire, you can remove the fuel (turn off the burner on the stove), the oxidizer (cover the fire with a special material), the heat (sprinkle water on the fire), or the reaction itself.
Combustion is, in some ways, the opposite of photosynthesis, an endothermic reaction in which light, water, and carbon dioxide enter to produce carbon.
It is tempting to assume that burning wood uses up the carbon found in the cellulose. However, there appears to be something more complex going on. If wood is exposed to heat, it undergoes pyrolysis (as opposed to combustion, which does not require oxygen), converting it into more flammable substances, such as gases, and it is these substances that ignite in fires.
If the wood burns long enough, the flame will disappear, but the smoldering will continue, and the wood in particular will continue to glow. Smoldering is incomplete combustion, which, in contrast to complete combustion, results in the formation of carbon monoxide.
Everyday objects constantly emit heat, much of it in the infrared range. Its wavelength is longer than visible light, so it cannot be seen without special cameras. The fire is bright enough to produce visible light, although it also produces infrared radiation.
Another mechanism for the appearance of color in fire is the emission spectrum of the object being burned. Unlike blackbody radiation, the radiation spectrum has discrete frequencies. This occurs due to the fact that electrons generate photons at certain frequencies, moving from a high-energy state to a low-energy state. These frequencies can be used to determine the elements present in a sample. A similar idea (using the absorption spectrum) is used to determine the composition of stars. The emission spectrum is also responsible for the color of fireworks and colored lights.
The shape of a flame on Earth depends on gravity. When a fire heats the surrounding air, convection occurs: hot air, containing, among other things, hot ash, rises, and cold air (containing oxygen) sinks, supporting the fire and giving the flame its shape. In low gravity, such as on a space station, this does not happen. Fire is fueled by the diffusion of oxygen, so it burns more slowly and in the form of a sphere (since combustion occurs only where the fire comes into contact with oxygen-containing air. There is no oxygen left inside the sphere).
Black body radiation
Blackbody radiation is described by Planck's formula, which relates to quantum mechanics. Historically, it was one of the first applications of quantum mechanics. It can be derived from quantum statistical mechanics as follows.We calculate the frequency distribution in a photon gas at temperature T. The fact that it coincides with the frequency distribution of photons emitted by an absolutely black body of the same temperature follows from Kirchhoff's radiation law. The idea is that the black body can be brought into temperature equilibrium with the photon gas (since they have the same temperature). The photonic gas is absorbed by the black body, which also emits photons, so for equilibrium it is necessary that for each frequency at which the black body emits radiation, it should absorb it at the same rate, which is determined by the frequency distribution in the gas.
In statistical mechanics, the probability of a system being in microstate s, if it is in thermal equilibrium at temperature T, is proportional
Where E s is the energy of state s, and β = 1 / k B T, or thermodynamic beta (T is temperature, k B is Boltzmann’s constant). This is the Boltzmann distribution. One explanation for this is given in Terence Tao's blog post. This means that the probability is equal
P s = (1/Z(β)) * e - β E s
Where Z(β) is the normalizing constant
Z(β) = ∑ s e - β E s
To describe the state of a photon gas, you need to know something about the quantum behavior of photons. In standard electromagnetic field quantization, the field can be viewed as a set of quantum harmonic oscillations, each oscillating at different angular frequencies ω. The energies of the eigenstates of a harmonic oscillator are denoted by a non-negative integer n ∈ ℤ ≥ 0, which can be interpreted as the number of photons of frequency ω. Eigenstate energies (up to a constant):
In turn, the quantum normalizing constant predicts that at low frequencies (relative to temperature) the classical answer is approximately correct, but at high frequencies the average energy falls off exponentially, with the drop being larger at lower temperatures. This happens because at high frequencies and low temperatures, a quantum harmonic oscillator spends most of its time in the ground state, and does not transition to the next level as easily, which is exponentially less likely to occur. Physicists say that most of this degree of freedom (the freedom of an oscillator to oscillate at a certain frequency) is “frozen.”
Density of states and Planck's formula
Now, knowing what happens at a certain frequency ω, it is necessary to sum over all possible frequencies. This part of the calculations is classical and no quantum corrections need to be made.We use the standard simplification that the photon gas is enclosed in a volume with a side of length L with periodic boundary conditions (that is, in reality it will be a flat torus T = ℝ 3 / L ℤ 3). Possible frequencies are classified according to solutions to the electromagnetic wave equation for standing waves in a volume with specified boundary conditions, which, in turn, correspond, up to a factor, to the eigenvalues of the Laplacian Δ. More precisely, if Δ υ = λ υ, where υ(x) is a smooth function T → ℝ, then the corresponding solution to the electromagnetic wave equation for a standing wave will be
υ(t, x) = e c √λ t υ(x)
And therefore, given that λ is usually negative, and therefore √λ is usually imaginary, the corresponding frequency will be equal to
ω = c √(-λ)
This frequency occurs dim V λ times, where V λ is the λ eigenvalue of the Laplacian.
We simplify the conditions using a volume with periodic boundary conditions because in this case it is very easy to write down all the eigenfunctions of the Laplacian. If we use complex numbers for simplicity, they are defined as
υ k (x) = e i k x
Where k = (k 1, k 2, k 3) ∈ 2 π / L * ℤ 3, wave vector. The corresponding eigenvalue of the Laplacian will be
λ k = - | k | 2 = - k 2 1 - k 2 2 - k 2 3
The corresponding frequency will be
And the corresponding energy (one photon of this frequency)
E k = ℏ ω k = ℏ c |k|
Here we approximate the probability distribution over possible frequencies ω k , which, strictly speaking, are discrete, by a continuous probability distribution, and calculate the corresponding density of states g(ω). The idea is that g(ω) dω should correspond to the number of available states with frequencies ranging from ω to ω + dω. We then integrate the density of states to obtain the final normalizing constant.
Why is this approximation reasonable? The complete normalizing constant can be described as follows. For each wave number k ∈ 2 π / L * ℤ 3 there is a number n k ∈ ℤ ≥0 that describes the number of photons with that wave number. The total number of photons n = ∑ n k is finite. Each photon adds ℏ ω k = ℏ c |k| to the energy, which means that
Z(β) = ∏ k Z ω k (β) = ∏ k 1 / (1 - e -βℏc|k|)
For all wave numbers k, therefore, its logarithm is written as the sum
Log Z(β) = ∑ k log 1 / (1 - e -βℏc|k|)
And we want to approximate this sum by an integral. It turns out that for reasonable temperatures and large volumes the integrand changes very slowly with k, so this approximation will be very close. It stops working only at ultra-low temperatures, where Bose-Einstein condensate occurs.
The density of states is calculated as follows. Wave vectors can be represented as uniform lattice points living in “phase space”, that is, the number of wave vectors in a certain region of phase space is proportional to its volume, at least for regions large compared to the lattice pitch 2π/L. Essentially, the number of wave vectors in the phase space region is equal to V/8π 3, where V = L 3, our limited volume.
It remains to calculate the volume of the phase space region for all wave vectors k with frequencies ω k = c |k| in the range from ω to ω + dω. This is a spherical shell with thickness dω/c and radius ω/c, so its volume
2πω 2 /c 3 dω
Therefore, the density of states for a photon
G(ω) dω = V ω 2 / 2 π 2 c 3 dω
In fact, this formula is twice as low: we forgot to take into account the polarization of the photons (or, equivalently, the spin of the photon), which doubles the number of states for a given wavenumber. Correct Density:
G(ω) dω = V ω 2 / π 2 c 3 dω
The fact that the density of states is linear in volume V works not only in a flat torus. This is a property of the eigenvalues of the Laplacian according to Weyl's law. This means that the logarithm of the normalizing constant
Log Z = V / π 2 c 3 ∫ ω 2 log 1 / (1 - e - βℏω) dω
The derivative with respect to β gives the average energy of the photon gas
< E >= - ∂/∂β log Z = V / π 2 c 3 ∫ ℏω 3 / (e βℏω - 1) dω
But what is important for us is the integrand, which gives the “energy density”
E(ω) dω = Vℏ / π 2 c 3 * ω 3 / (e βℏω - 1) dω
Describing the amount of photon gas energy originating from photons with frequencies in the range ω to ω + dω. The end result is a form of Planck's formula, although it requires a little fiddling to turn it into a formula that applies to black bodies rather than photonic gases (you need to divide by V to get the density per unit volume, and do a few more things to get measure of radiation).
Planck's formula has two limitations. In the case when βℏω → 0, the denominator tends to βℏω, and we get
E(ω) dω ≈ V / π 2 c 3 * ω 2 /β dω = V k B T ω 2 / π 2 c 3 dω
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After carrying out this simple experiment, you will be convinced that without oxygen the flame goes out. Take a candle and place it on a plate. Have an adult light the candle, then cover it with a glass jar. After a while you will see that the flame has gone out because the oxygen in the jar has run out.
A flame is formed during the combustion of substances in various states - they can be solid, liquid, and even gaseous. A flame is formed only in the presence of a flammable substance, oxygen and heat. Let's consider the process using the example of a match: sulfur and the match itself are a flammable substance, friction against the box; the energy resulting from friction becomes heat, and when it reacts with oxygen, the match begins to burn. By blowing on a burning match, the temperature drops and the combustion stops.
How is temperature measured?
Different scales are used to measure temperature. Each scale bears the name of its creator: Celsius, Fahrenheit, Kelvin and Rankine. Most countries use the Celsius (°C) scale.
Here are some example temperatures:
250 °C - ignition temperature of wood;
100 °C is the boiling point of water;
37 °C - human body temperature;
O °C is the freezing point of water;
- 39 °C - solidification temperature of mercury;
- 273 °C - absolute zero, the temperature at which atoms stop moving.
Combustion products
Smoke, ash and soot are combustion products. When a substance burns, it does not disappear, but turns into other substances and heat.
Flame shape
The flame has an elongated shape because hot air, lighter than cold air, rushes upward.
What is fuel or fuel?
Substances that burn in the presence of oxygen, releasing a large amount of heat, are called combustible and are used to produce various types of energy. Wood and coal are solid fuels. Gasoline, diesel fuel and kerosene are liquid fuels obtained from oil. Natural gas, consisting of methane, ethane, propane and butane, is a gaseous fuel.
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Candle fire, fire fire,
The fire of a mighty fire.
Lights - they are all masters
A gift sent down to people.
Introduction
He can be born, get stronger and grow. May weaken and die. Can be reverent and affectionate or cruel and greedy. It pounces, it devours, it consumes. You can fight him and he will retreat defeated. It can save you or turn into a terrible tragedy.
"Fire!" - this is both a cry of hope for the lost and a stern command that brings death to enemies.
Fiery hair, burning eyes, sizzling gaze. A flash of anger, a burst of laughter. Play with fire, catch fire with thoughts, glow with enthusiasm, burn with passion. “A small spark will give birth to a great flame”, “Fire and water will destroy everything”, “In fire, iron is melting”, “Fire is the friend and enemy of man.”
Enough examples. They just need to remind us what role this gift of nature plays in our lives. Our language has endowed it with the features of a living creature and, conversely, a person’s appearance and emotions are often associated with the properties of a flame.
Fire has long been an integral part of people's lives. Is it possible to imagine our existence without fire? Of course no. Modern man encounters combustion processes every day.
Purpose of the work: to study the combustion process from different points of view.
Study literature and Internet resources related to the topic of combustion;
Get acquainted with the history of mastering fire;
Find information and precise instructions for conducting experiments related to combustion processes.
Combustion- This is the first chemical reaction with which man became acquainted.
According to legend, fire was brought to frozen and unhappy people by the titan Prometheus, despite the prohibition of Zeus. But, most likely, primitive humanoid individuals encountered fire during fires caused by lightning strikes and volcanic eruptions. They did not know how to extract it themselves, but they could carry and maintain it. The first evidence of human use of fire comes from such archaeological sites of ancient man as Chesowanya in East Africa, Swartkrans in South Africa, Zhoukoudian and Xihoudu in China and Trinil on the island of Java. Fire pits, ashes and charcoals dating back to 1.5-2 million years ago, burnt tools of primitive people and mammal bones were found.
When people began to make fire on their own was not known for certain until 2008, when a group of Israeli archaeologists named a relatively precise date of 790 thousand years ago. Scientists made this conclusion based on the results of excavations at the famous Early Paleolithic site of Gesher Bnot Yaakov. According to a report in the journal Quaternary Science Reviews, they found traces of primitive fire-making techniques used throughout the nearly twelve generations that inhabited the area. Conclusions were also made on the basis of more detailed studies of stones and stone tools found here earlier.
The first way for humans to independently produce fire was friction. This method is occasionally used in our time, for example, in camping conditions.
Gradually, as humanity accumulated practical experience and new knowledge about the world around us, another method of making fire, based on striking a spark, came to replace it. It lies in the fact that when a stone hits certain minerals sharply, tiny particles fly out from their surface, which immediately ignite and, falling on the flammable material, set it on fire. These include, for example, pyrite (iron (II) disulfide - FeS 2). Other minerals with the same property are known. Over time, this method was improved: fire began to be produced by striking sparks from the more common and accessible mineral silicon with an iron rod. The flammable substances were tinder or burnt tow. To obtain fire in this way in Europe until the middle of the 19th century. The device used was called “flint” in Russia.
Another interesting method was used from ancient times to the mid-twentieth century by the tribes of the islands of Sumatra, Java, Kalimantan and Sulawesi: making fire by sharply compressing air in special devices.
Currently, people are constantly faced with combustion processes. This could be the combustion of gas in a gas stove, micro-explosions of fuel in diesel car engines, heating systems in private homes or the operation of a thermal power plant, etc. In military affairs, fire means shooting from a firearm.
Fire through the eyes of a scientist
What is fire? From a chemical point of view, this is a zone where an exothermic oxidation reaction occurs, sometimes accompanied by pyrolysis (thermal decomposition of organic and many inorganic compounds). From a physics point of view, it is the emission of light by heated substances from the zone of such a reaction.
Why do we see fire? Particles of combustible material and combustion products glow because they have a high temperature (usual blackbody radiation). High temperature allows atoms to move for some time to higher energy states, and then, upon returning to their original state, emit light of a certain frequency, which corresponds to the structure of the electron shells of a given element.
What is the difference between "fire" and "burning"? Fire is a fast form of combustion that releases both light and heat. Combustion- a complex physicochemical process of converting starting substances into combustion products during exothermic reactions. For the combustion process you need:
Combustible substance (fuel);
Oxidizing agent (most often oxygen);
Ignition source (not always)
The oxidizer and the combustible substance together make up the combustible system. It can be homogeneous and heterogeneous:
Homogeneous are systems in which a flammable substance and an oxidizer are evenly mixed with each other (mixtures of flammable gases, vapors). The combustion of such systems is called kinetic combustion. Under certain conditions, such combustion can have the character of an explosion.
Heterogeneous- systems in which the flammable substance and air are not mixed with each other and have interfaces (solid combustible materials and non-atomized liquids). During the combustion of inhomogeneous combustible systems, air oxygen penetrates through the combustion products to the combustible substance and reacts with it. This type of combustion is called diffusion combustion. Oxygen, chlorine, fluorine, bromine and other substances can act as an oxidizing agent.
Fire is the main (free-burning) phase of combustion, this is a physical and chemical phenomenon, which means that it is unreasonable to consider it only from a chemical point of view. From a physics point of view fire- a set of hot gases released as a result of:
arbitrary or involuntary heating of fuel (combustible substance) to a certain temperature in the presence of an oxidizer;
chemical reaction (for example, explosion);
flow of electric current in a medium (electric arc, electric welding)
The combustion process is divided into certain stages (phases):
1. Initial phase (growth stage),
2. Free burning phase (fully developed stage),
3. Smoldering phase (decay stage).
In the first - initial - phase, the flow of supply oxygen increases, then begins to decrease. A certain amount of heat is generated and this amount increases during the combustion process. The flame can reach temperatures in excess of 5370°C, but the room temperature at this stage may be low.
During the second, free-burning phase, oxygen-rich air is drawn into the flame as convection carries heat to the top layer of the confined space. Hot gases travel from top to bottom, forcing cooler air to seek lower levels, and ultimately ignite all the combustible material in the upper levels of the room. At this stage, the temperature in the upper layers may exceed 7000°C. The fire continues to consume free oxygen until it reaches a point where there is not enough oxygen to react with the fuel. The flame is reduced to a smoldering phase and only needs oxygen to ignite quickly.
In the third phase, the flame may stop if the combustion area is airtight. In this case, the combustion is reduced to smoldering embers. Dense smoke and gases are released and excess pressure occurs. The coals continue to smolder, the room will be completely filled with dense smoke and combustion gases at a temperature of 5370°C. Intense heat will evaporate lighter fuel constituents. , such as hydrogen and methane, from combustible material in the room. These fuel gases will combine with fire derivatives and further increase the risk of re-ignition and create the possibility of backdraft.
Types of combustion
Flash- this is the rapid combustion of a combustible mixture, not accompanied by the formation of compressed gases.
Fire- the occurrence of combustion under the influence of an ignition source.
A striking example of fire is the “trick” of ancient Indian priests: in ancient India, when performing sacred rites, in the twilight of temples, mysterious red lights suddenly flared up and scattered with sparks, instilling superstitious fear in the worshipers. Of course, the mighty Buddha had nothing to do with it, but his faithful servants, the priests, frightened and deceived believers with the help of sparklers. Strontium salts, which gave the flame a red color, were mixed with coal, sulfur and potassium chlorate (Berthollet salt). At the right moment, the mixture was set on fire.
2KClO 3 + S +2C = 2KCl + SO 2 + 2CO 2
Spontaneous combustion is a phenomenon of a sharp increase in the rate of exothermic reactions, leading to the combustion of substances (material, mixture) in the absence of an ignition source.
Thermal spontaneous combustion substances arise as a result of self-heating under the influence of a hidden or external heating source. Self-ignition is possible only if the amount of heat released during the auto-oxidation process exceeds the heat transfer to the environment.
An example of thermal spontaneous combustion is the spontaneous combustion of volatile essential oils in hot weather. The well-known legend about the burning bush, or Moses bush, has a completely scientific explanation: scientists believe that it was a diptam bush that secretes essential oils that light up when exposed to sunlight. In calm weather around the bush, the concentration of volatile essential oils released by the plant increases, which ignite when a certain temperature is reached. Equation of the chemical reaction of self-ignition of ether:
C 4 H 10 O + 6 O 2 = 4 CO 2 + 5 H 2 O
Thermal spontaneous combustion also explains the appearance of cemetery lights. When organic residues decompose, colorless, poisonous phosphine gas (PH3) is released, which has the property of spontaneously igniting in air, i.e. in the presence of oxygen. If this gas comes out of the ground, with organic residues decomposing in it, self-ignition occurs, small flashes are formed, with which churchmen used to frighten superstitious people. This phenomenon can only be observed in the warm season, since the auto-ignition temperature of phosphine = 38°C. Equation for the chemical reaction of self-ignition of phosphine:
2PH 3 + 4O 2 = P 2 O 5 + 3H 2 O
Spontaneous combustion can also occur under the influence of the vital activity of microorganisms in the mass of a substance (material, mixture).
Combustible materials have a tendency to microbiological spontaneous combustion, especially moistened ones, which serve as a breeding ground for microorganisms whose vital activity is associated with the release of heat (peat, sawdust). In this case, the self-heating temperature does not exceed normal ambient temperatures and can be negative.
Therefore, most fires and explosions occur when storing agricultural products (silage, moistened hay) in elevators. The most commonly used method to avoid self-heating and self-ignition of hay (and similar materials) is to ensure that the materials are not wetted when stored.
There is a difference between the processes of combustion and spontaneous combustion: in order for combustion to occur, it is necessary to introduce into the combustible system a thermal impulse having a temperature exceeding the temperature of spontaneous ignition of the substance.
Self-heating temperature- the minimum temperature of the environment, above which, under favorable conditions, the development of an exothermic self-heating process associated with thermal decomposition and oxidation of a certain volume (mass) of a combustible substance is possible.
Auto-ignition temperature- this is the lowest temperature of a substance at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of flaming combustion.
An explosion is an extremely rapid chemical transformation of a substance, accompanied by the rapid release of thermal energy and the formation of compressed gases capable of producing mechanical work.
It is also difficult to imagine the modern world without this type of combustion, since the mechanical explosion of fuel underlies the operation of most automobile engines. Small-scale explosions are also used in pyrotechnic devices. Pyrotechnics (ancient Greek πῦρ - fire, heat; τεχνικός - art, skill) is a branch of technology associated with the technologies of preparing flammable compositions and burning them to obtain a certain effect. Divided by:
military (flare guns, smoke bombs)
specialized (film special effects, civil signaling equipment)
entertainment (pyrotechnic products - firecrackers, sparklers, firecrackers, fireworks.
During the combustion process, combustion products are formed. They can be liquid, solid and gaseous. Their composition depends on the composition of the burning substance and on the conditions of its combustion. Organic and inorganic combustible substances consist mainly of carbon, oxygen, hydrogen, sulfur, phosphorus and nitrogen. Of these, carbon, hydrogen, sulfur and phosphorus are capable of oxidizing at combustion temperatures and forming combustion products: CO, CO 2, SO 2, P 2 O 5. Nitrogen does not oxidize at combustion temperature and is released in a free state, and oxygen is spent on the oxidation of the combustible elements of the substance. All of these combustion products (with the exception of carbon monoxide CO) are unable to burn in the future.
With incomplete combustion of organic substances under conditions of low temperatures and lack of air, more diverse products are formed - carbon monoxide (II), alcohols, aldehydes, acids and other complex chemical compounds. These products produce acrid and poisonous smoke. In addition, the products of incomplete combustion themselves are capable of burning and forming explosive mixtures with air. Such explosions occur when extinguishing fires in basements, dryers and in enclosed spaces with a large amount of flammable material.
Flame color
The ability of impurities to color flames in different colors is used not only in pyrotechnics, but also in analytical chemistry: pyrochemical analysis is a method for detecting certain chemical elements (for example, in minerals) by different colors of the flame.
|
Element |
Flame color |
|
Emerald green |
|
|
Cobalt (Co) |
|
|
Manganese (Mn) |
Violet-amethyst |
|
Iron (Fe) |
Yellow-brown |
|
Nickel (Ni) |
Red-brown |
|
Sodium (Na) |
Orange |
|
Calcium (Ca) |
Bright red |
The gas burner burns with a blue flame due to the presence of carbon monoxide (CO). The yellow-orange flame of a match is due to the presence of sodium salts in the wood. The yellow-orange color of the top of the flame under normal conditions is explained by the glow of soot particles carried upward by a stream of hot air.
Conclusion
As a result of work on the topic, the assigned tasks were completed: literary sources and Internet resources on the history of mastering fire and combustion processes were studied; laboratory experiments related to combustion processes and instructions for their implementation were selected.
The goal of the work has been achieved. Such a seemingly familiar phenomenon to modern man as combustion is a very complex physical and chemical process. This is the first chemical reaction with which man became acquainted! This process plays a very important role in our lives, although sometimes it poses a great danger.
Interesting facts and laboratory experiments presented in the work can be used for demonstration purposes in educational institutions to familiarize students with such an amazing topic as fire.
Practical part
Experience No. 1. "Chemical wick".
This method of remotely lighting bomb fuses was used back in the late 19th century. It is based on the ability of glycerin to ignite from a reaction with a strong oxidizing agent (potassium permanganate).
The purpose of the experiment: to make sure that fire can be “born” not only from a spark, but also simply from the mixing of certain substances, which individually are completely harmless.
Reagents and equipment: paper, crystalline potassium permanganate, anhydrous glycerin, pipette.
Progress of work and observations: pour a small amount of potassium permanganate onto a crumpled sheet of paper, drop 3-5 drops of glycerin; Smoke will appear above the mixture, and after some time (5-15 seconds) the mixture and the crumpled sheet will light up.
Experience No. 2. "Mini fireworks."
Reagents and equipment: powdered charcoal, crystalline potassium permanganate, iron filings, sheet of paper, crucible, crucible tongs, dry fuel.
Progress of work and observations: pour three small identical piles of finely crushed powders onto a sheet of paper: potassium permanganate, iron filings and coal. After this, fold a sheet of paper in half so that the powders fall into one pile. The fact is that when rubbing potassium permanganate with iron filings, the mixture can flare up. Pour the resulting mixture into the crucible. We bring it to the flame of dry fuel and wait a few seconds. When the mixture heats up, it will begin to sparkle like a sparkler.
Experience No. 3. "Unquenchable magnesium."
Magnesium is one of the few substances that cannot be extinguished with water.
Reagents and equipment: magnesium, water, glass, long-handled spoon, alcohol lamp.
Progress of work and observations: light a small amount of magnesium in a spoon from the flame of an alcohol lamp. We place burning magnesium in a glass of water, and observe that it does not go out, but continues to burn, remaining on the surface of the water.
Experiment No. 4 “Pharaoh’s snake from calcium gluconate.”
Pharaoh snakes are a number of reactions that are accompanied by the formation of a porous product from a small volume of reacting substances. These reactions are accompanied by rapid gas evolution.
Purpose of the experiment: to observe the thermal decomposition of calcium gluconate.
Reagents and equipment: calcium gluconate tablets, dry fuel, tweezers.
Progress of work and observations: on a lit tablet of dry fuel, using tweezers, place 1-2 tablets of calcium gluconate. Calcium gluconate will significantly increase in volume, take on a “worm-like” shape, and will “crawl” out of the flame. The resulting “snake” is very fragile and will fall apart at the first touch.
Experience No. 5. "Soda Viper"
The purpose of the experiment: to observe the thermal decomposition of a mixture of soda and powdered sugar.
Reagents and equipment: sand, soda, powdered sugar, alcohol.
Progress of work and observations: pour in a little sand (4-5 tablespoons), make a small depression at the top of the resulting “pyramid”. Pour a mixture of equal amounts of baking soda and powdered sugar into this cavity. We pour alcohol over it all and set it on fire. First, we observe the formation of small dark bubbles, then the appearance of the “soda viper” itself. As in the previous experiment, the pharaoh snake gradually increases in size.
Experience No. 6. "Explosion of a mixture of gases."
The purpose of the experiment: to observe the explosion of a mixture of air and flammable gas.
Reagents and equipment: zinc, hydrochloric acid, a device for producing gases, a glass of water, dishwashing detergent, a lit splinter.
Progress of work and observations: pour a little detergent into a glass of water, stir to form a light foam. We mix zinc and hydrochloric acid in a device for producing gases, and direct the gas outlet tube into a glass with water and detergent. When zinc reacts with hydrochloric acid, hydrogen is released, which forms foam in the glass. When there is enough
foam, remove the gas outlet tube, bring the burning splinter to the foam and observe a small explosion.
Experience No. 7. "Colored Flame"
Reagents and equipment: copper chloride, copper (II) sulfate, table salt, calcium fluoride, ammonium chloride, water, alcohol lamp, nichrome wire loop.
Progress of work and observations: mix ammonium chloride in a 1:1 ratio with each of the reagents, dilute with water and mix the resulting slurry. Then we hook a small amount of each substance with a loop of nichrome wire and add it to the burner flame, observing the flame coloring reaction. The result was: the original flame was transparent, with a bluish tint; sodium chloride (table salt) colored the flame yellow; copper (II) sulfate - copper sulfate - green; copper chloride turned it light blue, and calcium fluoride gave the flame a barely noticeable red tint.
Bibliography
1. .Kendivan, O.D.-S. A miracle through the eyes of a chemist / O.D.-S. Kendivan //Chemistry. Educational and methodological magazine for teachers of chemistry and natural science No. 5-6 ed. First of September - Moscow, 2014. - P.45-52
2. Krasitsky, V.A. Man-made fire: history and modernity / V.A. Krasitsky // Chemistry. Educational and methodological magazine for teachers of chemistry and natural science No. 1 ed. First of September - Moscow, 2014. - P.4-8
3. Unknown. Analytical chemistry. Semimicroanalysis [Electronic resource] / Unknown // Analytical chemistry - Access mode: http://analit-himiya.ucoz.com/index/0-13
4. Unknown. Combustion [Electronic resource]/ Unknown // Free encyclopedia Wikipedia - Access mode: https://ru.wikipedia.org/wiki/Combustion
5. Poltev, M.K. Chapter X. Fire safety. §1. Combustion processes / M.K. Poltev // Occupational safety in mechanical engineering, ed. "Higher School" - Moscow, 1980.
6. Ryumin, V.V. Combustion without air / V.V. Ryumin // Entertaining chemistry, 7th ed. Young guard. - Moscow, 1936. - P.58-59
7. Ryumin, V.V. Self-ignition / V.V. Ryumin // Entertaining chemistry, 7th ed. Young guard. - Moscow, 1936. - P.59
8. Stepin, B. D.; Alikberova, L.Yu. Spectacular experiments / B.D. Stepin, L.Yu. Alikberova // Entertaining tasks and spectacular experiments in chemistry, ed. Bustard - Moscow, 2006. - S.
During the combustion process, a flame is formed, the structure of which is determined by the reacting substances. Its structure is divided into areas depending on temperature indicators.
Definition
Flame refers to gases in hot form, in which plasma components or substances are present in solid dispersed form. Transformations of physical and chemical types are carried out in them, accompanied by glow, release of thermal energy and heating.
The presence of ionic and radical particles in a gaseous medium characterizes its electrical conductivity and special behavior in an electromagnetic field.
What are flames
This is usually the name given to processes associated with combustion. Compared to air, gas density is lower, but high temperatures cause gas to rise. This is how flames are formed, which can be long or short. Often there is a smooth transition from one form to another.
Flame: structure and structure
To determine the appearance of the described phenomenon, it is enough to light it. The non-luminous flame that appears cannot be called homogeneous. Visually, three main areas can be distinguished. By the way, studying the structure of a flame shows that different substances burn with the formation of different types of torch.
When a mixture of gas and air burns, a short torch is first formed, the color of which has blue and violet shades. The core is visible in it - green-blue, reminiscent of a cone. Let's consider this flame. Its structure is divided into three zones:
- A preparatory area is identified in which the mixture of gas and air is heated as it exits the burner opening.
- This is followed by the zone in which combustion occurs. It occupies the top of the cone.
- When there is insufficient air flow, the gas does not burn completely. Carbon divalent oxide and hydrogen residues are released. Their combustion takes place in the third region, where there is oxygen access.
Now we will separately consider different combustion processes.
Burning candle
Burning a candle is similar to burning a match or lighter. And the structure of a candle flame resembles a hot gas stream, which is pulled upward due to buoyant forces. The process begins with heating the wick, followed by evaporation of the wax.
The lowest zone, located inside and adjacent to the thread, is called the first region. It has a slight glow due to a large amount of fuel, but a small volume of oxygen mixture. Here, the process of incomplete combustion of substances occurs, releasing which is subsequently oxidized.
The first zone is surrounded by a luminous second shell, which characterizes the structure of the candle flame. A larger volume of oxygen enters it, which causes the continuation of the oxidation reaction with the participation of fuel molecules. Temperatures here will be higher than in the dark zone, but not sufficient for final decomposition. It is in the first two areas that when droplets of unburned fuel and coal particles are strongly heated, a luminous effect appears.
The second zone is surrounded by a low-visibility shell with high temperature values. Many oxygen molecules enter it, which contributes to the complete combustion of fuel particles. After the oxidation of substances, the luminous effect is not observed in the third zone.
Schematic illustration
For clarity, we present to your attention an image of a burning candle. Flame circuit includes:
- The first or dark area.
- Second luminous zone.
- The third transparent shell.
The candle thread does not burn, but only charring of the bent end occurs.
Burning alcohol lamp
For chemical experiments, small tanks of alcohol are often used. They are called alcohol lamps. The burner wick is soaked with liquid fuel poured through the hole. This is facilitated by capillary pressure. When the free top of the wick is reached, the alcohol begins to evaporate. In the vapor state, it is ignited and burns at a temperature of no more than 900 °C.
The flame of an alcohol lamp has a normal shape, it is almost colorless, with a slight tint of blue. Its zones are not as clearly visible as those of a candle.
Named after the scientist Barthel, the beginning of the fire is located above the burner grid. This deepening of the flame leads to a decrease in the inner dark cone, and the middle section, which is considered the hottest, emerges from the hole.
Color characteristic
Various radiations are caused by electronic transitions. They are also called thermal. Thus, as a result of combustion of a hydrocarbon component in air, a blue flame is caused by the release of an H-C compound. And when C-C particles are emitted, the torch turns orange-red.
It is difficult to consider the structure of a flame, the chemistry of which includes compounds of water, carbon dioxide and carbon monoxide, and the OH bond. Its tongues are practically colorless, since the above particles, when burned, emit radiation in the ultraviolet and infrared spectrum.
The color of the flame is interconnected with temperature indicators, with the presence of ionic particles in it, which belong to a certain emission or optical spectrum. Thus, the combustion of certain elements leads to a change in the color of the fire in the burner. Differences in the color of the torch are associated with the arrangement of elements in different groups of the periodic system.
Fire is examined with a spectroscope for the presence of radiation in the visible spectrum. At the same time, it was found that simple substances from the general subgroup also cause a similar coloration of the flame. For clarity, sodium combustion is used as a test for this metal. When brought into the flame, the tongues turn bright yellow. Based on the color characteristics, the sodium line is identified in the emission spectrum.
It is characterized by the property of rapid excitation of light radiation from atomic particles. When non-volatile compounds of such elements are introduced into the fire of a Bunsen burner, it becomes colored.
Spectroscopic examination shows characteristic lines in the area visible to the human eye. The speed of excitation of light radiation and the simple spectral structure are closely related to the high electropositive characteristics of these metals.
Characteristic
The flame classification is based on the following characteristics:
- aggregate state of burning compounds. They come in gaseous, airborne, solid and liquid forms;
- type of radiation, which can be colorless, luminous and colored;
- distribution speed. There is fast and slow spread;
- flame height. The structure can be short or long;
- nature of movement of reacting mixtures. There are pulsating, laminar, turbulent movement;
- visual perception. Substances burn with the release of a smoky, colored or transparent flame;
- temperature indicator. The flame can be low temperature, cold and high temperature.
- state of the fuel - oxidizing reagent phase.
Combustion occurs as a result of diffusion or pre-mixing of the active components.
Oxidative and reduction region
The oxidation process occurs in a barely noticeable zone. It is the hottest and is located at the top. In it, fuel particles undergo complete combustion. And the presence of oxygen excess and combustible deficiency leads to an intense oxidation process. This feature should be used when heating objects over the burner. That is why the substance is immersed in the upper part of the flame. This combustion proceeds much faster.
Reduction reactions take place in the central and lower parts of the flame. It contains a large supply of flammable substances and a small amount of O 2 molecules that carry out combustion. When introduced into these areas, the O element is eliminated.
As an example of a reducing flame, the process of splitting ferrous sulfate is used. When FeSO 4 enters the central part of the burner torch, it first heats up and then decomposes into ferric oxide, anhydride and sulfur dioxide. In this reaction, reduction of S with a charge of +6 to +4 is observed.
Welding flame
This type of fire is formed as a result of the combustion of a mixture of gas or liquid vapor with oxygen from clean air.
An example is the formation of an oxyacetylene flame. It distinguishes:
- core zone;
- middle recovery area;
- flare extreme zone.
This is how many gas-oxygen mixtures burn. Differences in the ratio of acetylene to oxidizer result in different flame types. It can be of normal, carburizing (acetylenic) and oxidizing structure.
Theoretically, the process of incomplete combustion of acetylene in pure oxygen can be characterized by the following equation: HCCH + O 2 → H 2 + CO + CO (one mole of O 2 is required for the reaction).
The resulting molecular hydrogen and carbon monoxide react with air oxygen. The final products are water and tetravalent carbon oxide. The equation looks like this: CO + CO + H 2 + 1½O 2 → CO 2 + CO 2 +H 2 O. This reaction requires 1.5 moles of oxygen. When summing up O 2, it turns out that 2.5 moles are spent per 1 mole of HCCH. And since in practice it is difficult to find ideally pure oxygen (often it is slightly contaminated with impurities), the ratio of O 2 to HCCH will be 1.10 to 1.20.
When the oxygen to acetylene ratio is less than 1.10, a carburizing flame occurs. Its structure has an enlarged core, its outlines become blurry. Soot is released from such a fire due to a lack of oxygen molecules.
If the gas ratio is greater than 1.20, then an oxidizing flame with an excess of oxygen is obtained. Its excess molecules destroy iron atoms and other components of the steel burner. In such a flame, the nuclear part becomes short and has points.
Temperature indicators
Each fire zone of a candle or burner has its own values, determined by the supply of oxygen molecules. The temperature of the open flame in its different parts ranges from 300 °C to 1600 °C.
An example is a diffusion and laminar flame, which is formed by three shells. Its cone consists of a dark area with a temperature of up to 360 °C and a lack of oxidizing substances. Above it is a glow zone. Its temperature ranges from 550 to 850 °C, which promotes thermal decomposition of the combustible mixture and its combustion.
The outer area is barely noticeable. In it, the flame temperature reaches 1560 °C, which is due to the natural characteristics of fuel molecules and the speed of entry of the oxidizing substance. This is where the combustion is most energetic.
Substances ignite under different temperature conditions. Thus, magnesium metal burns only at 2210 °C. For many solids the flame temperature is around 350°C. Matches and kerosene can ignite at 800 °C, while wood can ignite from 850 °C to 950 °C.
The cigarette burns with a flame whose temperature varies from 690 to 790 °C, and in a propane-butane mixture - from 790 °C to 1960 °C. Gasoline ignites at 1350 °C. The alcohol combustion flame has a temperature of no more than 900 °C.
How to curse the darkness
It's better to at least light it
one small candle.
Confucius
At first
The first attempts to understand the combustion mechanism are associated with the names of the Englishman Robert Boyle, the Frenchman Antoine Laurent Lavoisier and the Russian Mikhail Vasilyevich Lomonosov. It turned out that during combustion the substance does not “disappear” anywhere, as was once naively believed, but turns into other substances, mostly gaseous and therefore invisible. Lavoisier was the first to show in 1774 that during combustion, approximately a fifth of it is lost from the air. During the 19th century, scientists studied in detail the physical and chemical processes that accompany combustion. The need for such work was caused primarily by fires and explosions in mines.
But only in the last quarter of the twentieth century were the main chemical reactions accompanying combustion identified, and to this day many dark spots remain in the chemistry of flame. They are studied using the most modern methods in many laboratories. These studies have several goals. On the one hand, it is necessary to optimize combustion processes in the furnaces of thermal power plants and in the cylinders of internal combustion engines, to prevent explosive combustion (detonation) when the air-gasoline mixture is compressed in a car cylinder. On the other hand, it is necessary to reduce the amount of harmful substances formed during the combustion process, and at the same time, to look for more effective means of extinguishing the fire.
There are two types of flame. Fuel and oxidizer (most often oxygen) can be forced or spontaneously supplied to the combustion zone separately and mixed in the flame. Or they can be mixed in advance - such mixtures can burn or even explode in the absence of air, such as gunpowder, pyrotechnic mixtures for fireworks, rocket fuel. Combustion can occur both with the participation of oxygen entering the combustion zone with air, and with the help of oxygen contained in the oxidizing substance. One of these substances is Berthollet salt (potassium chlorate KClO 3); this substance easily gives up oxygen. A strong oxidizing agent is nitric acid HNO 3: in its pure form it ignites many organic substances. Nitrates, salts of nitric acid (for example, in the form of fertilizer - potassium or ammonium nitrate), are highly flammable if mixed with flammable substances. Another powerful oxidizer, nitrogen tetroxide N 2 O 4 is a component of rocket fuels. Oxygen can also be replaced by strong oxidizing agents such as chlorine, in which many substances burn, or fluorine. Pure fluorine is one of the most powerful oxidizing agents; water burns in its stream.
Chain reactions
The foundations of the theory of combustion and flame propagation were laid in the late 20s of the last century. As a result of these studies, branched chain reactions were discovered. For this discovery, Russian physical chemist Nikolai Nikolaevich Semenov and English researcher Cyril Hinshelwood were awarded the Nobel Prize in Chemistry in 1956. Simpler unbranched chain reactions were discovered back in 1913 by the German chemist Max Bodenstein using the example of the reaction of hydrogen with chlorine. The overall reaction is expressed by the simple equation H 2 + Cl 2 = 2HCl. In fact, it involves very active fragments of molecules - the so-called free radicals. Under the influence of light in the ultraviolet and blue regions of the spectrum or at high temperatures, chlorine molecules disintegrate into atoms, which begin a long (sometimes up to a million links) chain of transformations; Each of these transformations is called an elementary reaction:
Cl + H 2 → HCl + H,
H + Cl 2 → HCl + Cl, etc.
At each stage (reaction link), one active center (hydrogen or chlorine atom) disappears and at the same time a new active center appears, continuing the chain. The chains break when two active species meet, for example Cl + Cl → Cl 2. Each chain propagates very quickly, so if the "initial" active particles are generated at high speed, the reaction will proceed so quickly that it can lead to an explosion.
N. N. Semenov and Hinshelwood discovered that the combustion reactions of phosphorus and hydrogen vapors proceed differently: the slightest spark or open flame can cause an explosion even at room temperature. These reactions are branched chain reactions: active particles “multiply” during the reaction, that is, when one active particle disappears, two or three appear. For example, in a mixture of hydrogen and oxygen, which can be quietly stored for hundreds of years if there are no external influences, the appearance of active hydrogen atoms for one reason or another triggers the following process:
H + O 2 → OH + O,
O + H 2 → OH + H.
Thus, in an insignificant period of time, one active particle (H atom) turns into three (a hydrogen atom and two OH hydroxyl radicals), which already launch three chains instead of one. As a result, the number of chains grows like an avalanche, which instantly leads to an explosion of the mixture of hydrogen and oxygen, since a lot of thermal energy is released in this reaction. Oxygen atoms are present in flames and in the combustion of other substances. They can be detected by directing a stream of compressed air across the top of the burner flame. At the same time, a characteristic smell of ozone will be detected in the air - these are oxygen atoms “sticking” to oxygen molecules to form ozone molecules: O + O 2 = O 3, which were carried out of the flame by cold air.
The possibility of an explosion of a mixture of oxygen (or air) with many flammable gases - hydrogen, carbon monoxide, methane, acetylene - depends on the conditions, mainly on the temperature, composition and pressure of the mixture. So, if, as a result of a leak of household gas in the kitchen (it consists mainly of methane), its content in the air exceeds 5%, then the mixture will explode from the flame of a match or lighter, and even from a small spark that slips through the switch when turning on the light. There will be no explosion if the chains break faster than they can branch. This is why the lamp for miners, which the English chemist Humphry Davy developed in 1816, without knowing anything about the chemistry of flame, was safe. In this lamp, the open flame was fenced off from the external atmosphere (which could be explosive) with a thick metal mesh. On the metal surface, active particles effectively disappear, turning into stable molecules, and therefore cannot penetrate into the external environment.
The complete mechanism of branched chain reactions is very complex and can include more than a hundred elementary reactions. Many oxidation and combustion reactions of inorganic and organic compounds are branched chain reactions. The same will be the reaction of fission of nuclei of heavy elements, for example plutonium or uranium, under the influence of neutrons, which act as analogues of active particles in chemical reactions. Penetrating into the nucleus of a heavy element, neutrons cause its fission, which is accompanied by the release of very high energy; At the same time, new neutrons are emitted from the nucleus, which cause the fission of neighboring nuclei. Chemical and nuclear branched chain processes are described by similar mathematical models.
What do you need to get started?
For combustion to begin, a number of conditions must be met. First of all, the temperature of the flammable substance must exceed a certain limit value, which is called the ignition temperature. Ray Bradbury's famous novel Fahrenheit 451 is so named because at approximately this temperature (233°C) paper catches fire. This is the “ignition temperature” above which solid fuels release flammable vapors or gaseous decomposition products in quantities sufficient for their stable combustion. The ignition temperature of dry pine wood is approximately the same.
The flame temperature depends on the nature of the combustible substance and the combustion conditions. Thus, the temperature in a methane flame in air reaches 1900°C, and when burning in oxygen - 2700°C. An even hotter flame is produced when hydrogen (2800°C) and acetylene (3000°C) are burned in pure oxygen. No wonder the flame of an acetylene torch easily cuts almost any metal. The highest temperature, about 5000°C (it is recorded in the Guinness Book of Records), is obtained when burned in oxygen by a low-boiling liquid - carbon subnitride C 4 N 2 (this substance has the structure of dicyanoacetylene NC–C=C–CN). And according to some information, when it burns in an ozone atmosphere, the temperature can reach up to 5700°C. If this liquid is set on fire in air, it will burn with a red, smoky flame with a green-violet border. On the other hand, cold flames are also known. For example, phosphorus vapors burn at low pressures. A relatively cold flame is also obtained during the oxidation of carbon disulfide and light hydrocarbons under certain conditions; for example, propane produces a cool flame at reduced pressure and temperatures between 260–320°C.
Only in the last quarter of the twentieth century did the mechanism of processes occurring in the flames of many combustible substances begin to become clearer. This mechanism is very complex. The original molecules are usually too large to react directly with oxygen into reaction products. For example, the combustion of octane, one of the components of gasoline, is expressed by the equation 2C 8 H 18 + 25 O 2 = 16 CO 2 + 18 H 2 O. However, all 8 carbon atoms and 18 hydrogen atoms in an octane molecule cannot simultaneously combine with 50 oxygen atoms : for this to happen, many chemical bonds must be broken and many new ones must be formed. The combustion reaction occurs in many stages - so that at each stage only a small number of chemical bonds are broken and formed, and the process consists of many sequentially occurring elementary reactions, the totality of which appears to the observer as a flame. It is difficult to study elementary reactions primarily because the concentrations of reactive intermediate particles in the flame are extremely small.
Inside the flame
Optical probing of different areas of the flame using lasers made it possible to establish the qualitative and quantitative composition of the active particles present there - fragments of molecules of a combustible substance. It turned out that even in the seemingly simple reaction of combustion of hydrogen in oxygen 2H 2 + O 2 = 2H 2 O, more than 20 elementary reactions occur with the participation of molecules O 2, H 2, O 3, H 2 O 2, H 2 O, active particles N, O, OH, BUT 2. Here, for example, is what the English chemist Kenneth Bailey wrote about this reaction in 1937: “The equation for the reaction of hydrogen with oxygen is the first equation that most beginners in chemistry become familiar with. This reaction seems very simple to them. But even professional chemists are somewhat amazed to see a hundred-page book entitled “The Reaction of Oxygen with Hydrogen,” published by Hinshelwood and Williamson in 1934.” To this we can add that in 1948 a much larger monograph by A. B. Nalbandyan and V. V. Voevodsky was published entitled “The Mechanism of Hydrogen Oxidation and Combustion.”
Modern research methods have made it possible to study the individual stages of such processes and measure the rate at which various active particles react with each other and with stable molecules at different temperatures. Knowing the mechanism of individual stages of the process, it is possible to “assemble” the entire process, that is, to simulate a flame. The complexity of such modeling lies not only in studying the entire complex of elementary chemical reactions, but also in the need to take into account the processes of particle diffusion, heat transfer and convection flows in the flame (it is the latter that create the fascinating play of tongues of a burning fire).
Where does everything come from?
The main fuel of modern industry is hydrocarbons, ranging from the simplest, methane, to heavy hydrocarbons, which are contained in fuel oil. The flame of even the simplest hydrocarbon, methane, can involve up to a hundred elementary reactions. However, not all of them have been studied in sufficient detail. When heavy hydrocarbons, such as those found in paraffin, burn, their molecules cannot reach the combustion zone without remaining intact. Even on approaching the flame, due to the high temperature, they split into fragments. In this case, groups containing two carbon atoms are usually split off from molecules, for example C 8 H 18 → C 2 H 5 + C 6 H 13. Active species with an odd number of carbon atoms can abstract hydrogen atoms, forming compounds with double C=C and triple C≡C bonds. It was discovered that in a flame such compounds can enter into reactions that were not previously known to chemists, since they do not occur outside the flame, for example C 2 H 2 + O → CH 2 + CO, CH 2 + O 2 → CO 2 + H + N.
The gradual loss of hydrogen by the initial molecules leads to an increase in the proportion of carbon in them, until particles C 2 H 2, C 2 H, C 2 are formed. The blue-blue flame zone is due to the glow of excited C 2 and CH particles in this zone. If the access of oxygen to the combustion zone is limited, then these particles do not oxidize, but are collected into aggregates - they polymerize according to the scheme C 2 H + C 2 H 2 → C 4 H 2 + H, C 2 H + C 4 H 2 → C 6 H 2 + N, etc.
The result is soot particles consisting almost exclusively of carbon atoms. They are shaped like tiny balls, up to 0.1 micrometers in diameter, that contain approximately a million carbon atoms. Such particles at high temperatures produce a well-luminous yellow flame. At the top of the candle flame, these particles burn, so the candle does not smoke. If further adhesion of these aerosol particles occurs, larger soot particles are formed. As a result, the flame (for example, burning rubber) produces black smoke. Such smoke appears if the proportion of carbon relative to hydrogen in the original fuel is increased. An example is turpentine - a mixture of hydrocarbons with the composition C 10 H 16 (C n H 2n–4), benzene C 6 H 6 (C n H 2n–6), and other flammable liquids with a lack of hydrogen - all of them smoke when burned. A smoky and brightly luminous flame is produced by acetylene C 2 H 2 (C n H 2n–2) burning in air; Once upon a time, such a flame was used in acetylene lanterns mounted on bicycles and cars, and in miners' lamps. And vice versa: hydrocarbons with a high hydrogen content - methane CH 4, ethane C 2 H 6, propane C 3 H 8, butane C 4 H 10 (general formula C n H 2n + 2) - burn with sufficient air access with an almost colorless flame. A mixture of propane and butane in the form of a liquid under low pressure is found in lighters, as well as in cylinders used by summer residents and tourists; the same cylinders are installed in gas-powered cars. More recently, it was discovered that soot often contains spherical molecules consisting of 60 carbon atoms; they were called fullerenes, and the discovery of this new form of carbon was marked by the award of the Nobel Prize in Chemistry in 1996.
