The emergence of structural chemistry meant that there was an opportunity for targeted qualitative transformation of substances, creating a scheme for the synthesis of any chemical compounds, including previously unknown ones.
The nature of any chemical compound depends not only on the qualitative and quantitative composition, but also on the mutual influence of atoms and the structure of the molecule.
Structure of matter and its properties
Substances that have the same composition but different structures are called isomers, and the phenomenon itself - isomerism. For example, f The formula C 4 H 8 O has 21 substances.
To describe the properties of substances, you need to know not only the composition, but also connection structure. This is of particular importance for organic chemistry. Electrons of one chemical element, interacting with the nucleus and electrons of another chemical element, turn out to be strictly localized (located) in space. Since an electron is an electromagnetic wave with a certain area of propagation, this area has a direction. That is, a chemical bond is formed in a certain direction in space and determines the spatial orientation of atoms.
Molecule structure– spatial and energy orderliness of a system consisting of atomic nuclei and electrons.
An important phenomenon in organic chemistry called isomerism is associated with the spatial structure of a molecule.
Isomers- substances that have the same composition, but a different molecular structure.
Structural chemistry has become a higher level in relation to the study of the composition of matter. At the same time, chemistry turned from a predominantly analytical science into a synthetic science. The main achievement of this stage in the development of chemistry was the establishment of a connection between the structure of molecules and the reactivity of substances.
The four main states of matter - plasma, gaseous, liquid and solid (listed in order of existence as the temperature decreases) have been known for a long time, but today scientists identify two more states - low-temperature condensates. Condensate is a new state of matter at ultra-low temperatures - less than 0.00000001 K (!!!), i.e. at temperatures below the temperature of the vacuum of space (in space the temperature is about 3 K).
Let us use a specific example of a solid to show the influence of the atomic structure on the properties of the material. To do this, we will choose a simple monatomic material - carbon.
In the solid state, carbon can be crystalline or amorphous, and each of its states has its own name.
1. Soot - amorphous carbon in the form of a finely ground powder (it has now been established that in its structure in soot, coke, glassy carbon and similar materials, carbon to varying degrees approaches graphite. Speaking about the properties of soot, it can be noted that electrical conductivity soot is zero, i.e. soot is an electrical insulator.
2. Until the early 60s, it was believed that only two crystalline forms of pure carbon exist in nature, namely three- and two-dimensional polymers, i.e. diamond and graphite. The structure of graphite is characterized by layers; atoms in the layers are strongly bonded to each other, while interlayer interactions are negligible. Therefore, graphite easily splits into layers; it is a soft crystalline material. Unlike soot, graphite is a very good conductor of electricity.
3. Diamond has a cubic crystal structure, built from the same carbon atoms. Unlike graphite, diamond is a hard crystalline material (perhaps the hardest). Such properties are associated with its structure, since all atoms are equidistant from each other and tightly “bound” to each other/
4. In 1985, a large family of spherical carbon molecules - fullerenes - was discovered. Fullerenes are a new type of carbon. These are closed molecules of the type C 60, C 70, C 74 ..., in which all carbon atoms are located on a “spherical” surface. In the structure of fullerene C 60 (the diameter of the molecule is about 1 nm), carbon atoms are located at the vertices of regular hexagons or pentagons (in the condensed (crystalline) state, fullerenes are called fullerites). Fullerenes have been found in some natural minerals, for example, in Karelian shungite. New classes of substances have been synthesized based on fullerene: for example, fullerides have been obtained by interacting with metals.
The interesting properties of these materials are associated with the “capture inside” of the ball of various atoms - Na, K. The resulting fullerides have superconductivity (at temperatures of 19-55 K), and when using platinum group metals, ferromagnetic properties are additionally manifested. An interesting property of fullerenes at low temperatures and pressure is the ability to absorb hydrogen. In this regard, it is possible to use fullerenes as a basis for the production of rechargeable batteries. The fullerene capsule can contain drugs that will be selectively delivered to the damaged organ or tissue/
5. Graphite nanotubes are a new type of carbon, obtained in 1991. A carbon nanotube can be represented as a graphite plane rolled into a cylinder. Tubes can be single-walled or multi-walled if they are made from several graphite layers. The diameter of the tube ranges from one to several tens of nanometers, and the length can reach several centimeters; usually the tubes end in a hemispherical head. Carbon nanotubes have unique mechanical (very strong), electrical and thermal properties (electrical and thermal conductivity approached or exceeded those of metals).
6. The 2010 Nobel Prize in Physics was awarded to Andre Geim and Konstantin Novoselov, Russians working in the UK, “for their pioneering experiments in the study of the two-dimensional material graphene.” In 2004, they experimentally proved the possibility of obtaining a special form of carbon, which is a sheet one atom thick, connected into a two-dimensional crystal lattice of regular hexagons. In other words, graphene is one separate layer of the well-known graphite. Graphene is the thinnest and strongest known material; on the other hand, it is very flexible, capable of exhibiting the properties of both a conductor (remember graphite) and a semiconductor.
Modern structural chemistry has achieved great results. The synthesis of new organic substances makes it possible to obtain useful and valuable materials not found in nature. Thus, every year thousands of kilograms of ascorbic acid (vitamin C) and many new drugs are synthesized around the world, including harmless antibiotics, drugs against hypertension, peptic ulcers, etc.
The most recent achievement in structural chemistry is the discovery of a completely new class of organometallic compounds, which, due to their two-layer structure, are called “sandwich” compounds. The molecule of this substance consists of two plates of hydrogen and carbon compounds, between which there is an atom of a metal.
Research in the field of modern structural chemistry is proceeding in two promising directions:
1) synthesis of crystals with maximum approximation to the ideal lattice to obtain materials with high technical indicators: maximum strength, thermal resistance, durability, etc.;
2) creation of crystals with pre-programmed crystal lattice defects for the production of materials with specified electrical, magnetic and other properties.
3. General characteristics of solutions
The physical properties of water are completely anomalous. The most amazing of them is its ability to be a liquid under normal conditions. Molecules of similar chemical compounds (H 2 S or H 2 Se) are much heavier than water, but under these conditions they are gaseous.
The triple point of water, i.e. balance of water, ice and steam, observed at a temperature of 0.01 °C and a pressure of 611 Pa (Fig. 8.1). Supercooled water, i.e., remaining in a liquid state below 0°C, behaves strangely: on the one hand, its density decreases with decreasing temperature, on the other hand, it approaches the density of ice
Extraordinary the limits of permissible values of undercooling and overheating are large water: you can keep it in a liquid state at temperatures from -40 to +200 °C.
Unlike most other liquids, as the temperature increases, its specific volume decreases and its density increases, reaching a minimum (respectively maximum) at 4 °C. In ordinary liquids, density always decreases with decreasing temperature.
When freezing, the volume of water increases up to 10%. The density of water is greater than the density of ice. When crystals melt, when the regularity of ion packing is disrupted, the density decreases by 2-4%. This property of water protects reservoirs from complete freezing, saving life in them. Ice is a poor conductor of heat.
Very high heat capacity water- when ice melts, it more than doubles. Therefore, the seas and oceans are giant thermostats, smoothing out all fluctuations in air temperature. By the way, water vapor in the atmosphere can also perform these same functions. The lack of water vapor in deserts leads to sharp fluctuations in night and day temperatures.
Water is a universal solvent. The rule of dissolution is that like dissolves into like.
The main difference between water is its hydrogen bonds.(Fig. 8.2),
A water molecule is a small dipole, containing positive and negative charges at the poles. If you connect the epicenters of positive and negative charges with straight lines, you get a three-dimensional geometric figure - a regular tetrahedron
The complex of water molecules exists in the gaseous state, in liquid water and in ice. But, as L. Pauling established, ice is not a crystal with complete ordering even at O K. The structure of ice is quite loose: each cavity is surrounded by six H 2 0 molecules, and each molecule is surrounded by six cavities. The size of these cavities is such that they can accommodate one molecule without disturbing the hydrogen bonding framework.
A substance is an acid if it dissociates in water to form hydrogen ions, and a base if it is capable of adding hydrogen ions in solution or forming hydroxide ions OH. The acidity or alkalinity of a solution is characterized by pH, the scale of which covers values from 0 to 14. This scale is logarithmic, i.e. The logarithms of the concentration of hydrogen ions are plotted on it. The acidity of a solution with pH 5 is 10 times greater than with pH 6, and 100 times greater than with pH 7. A solution with pH 6 contains one millionth of a mole of hydrogen ions per 1 liter, pH 7 corresponds to a neutral environment, and below that are more acidic environments, and above - alkaline.
A chemical process (from the Latin processus - advancement) is a sequential change of states of matter, representing a continuous, unified movement. The process of converting one substance into another substance is called chemical reaction. Van't Hoff, using a thermodynamic approach, classified chemical reactions and also formulated the basic principles of chemical kinetics.
About 10,000 chemical reactions take place in each cell.
Chemical processes are divided into:
homo- And heterogeneous(depending on the state of aggregation of the reacting systems),
exo- And endothermic(depending on the amount of heat released and absorbed),
redox(depending on the change in the oxidation state of a substance associated with the transfer of electrons from some atoms (reducing agent) to other atoms (oxidizing agent).
He studies the speed and characteristics of chemical reactions. chemical kinetics.
The rate of a chemical reaction is also affected by the following conditions and parameters:
1) nature reacting substances (for example, alkali metals dissolve in water with the formation of alkalis and the release of hydrogen, and the reaction proceeds instantly under normal conditions, while zinc, iron and others react slowly and form oxides, and noble metals do not react at all);
2) temperature. For every 10 °C increase in temperature, the reaction rate increases by 2-4 times (van't Hoff's rule). Oxygen begins to react with many substances at a noticeable speed already at ordinary temperatures (slow oxidation). As the temperature rises, a violent reaction (combustion) begins;
3) concentration. For dissolved substances and gases, the rate of chemical reactions depends on the concentration of the reacting substances. Combustion of substances in pure oxygen occurs more intensely than in air, where the oxygen concentration is almost 5 times less. The law of mass action is valid here: at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the concentration of the reacting substances;
4)reaction surface area. For substances in the solid state, the rate is directly proportional to the surface area of the reacting substances. Iron and sulfur in the solid state react quickly enough only with preliminary grinding and mixing: burning brushwood and logs;
5)catalyst. The speed of a reaction depends on catalysts, substances that speed up chemical reactions without being consumed. IN. Ostwald, studying the conditions of chemical equilibrium, came to the discovery of the phenomenon of catalysis. The decomposition of berthollet salt and hydrogen peroxide is accelerated in the presence of manganese (IV) oxide, etc.
Catalysts are positive, which speed up the reaction, and negative (inhibitors), which slow it down. Catalytic selective acceleration of a chemical reaction is called catalysis and is a technique of modern chemical technology (production of polymer materials, synthetic fuels, etc.). It is believed that the share of catalytic processes in the chemical industry reaches 80%.
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Introduction
Under the influence of new production requirements, the doctrine of chemical processes arose, which takes into account changes in the properties of a substance under the influence of temperature, pressure, solvents and other factors. After this, chemistry becomes a science not only and not so much about substances as complete objects, but also a science about the processes and mechanisms of change in matter. Thanks to this, it ensured the creation of the production of synthetic materials that replace wood and metal in construction work, food raw materials in the production of drying oil, varnishes, detergents and lubricants. The production of artificial fibers, rubbers, ethyl alcohol and many solvents began to be based on petroleum raw materials, and the production of nitrogen fertilizers was based on air nitrogen. Petrochemical production technology has emerged with its flow systems providing continuous, high-performance processes. chemical reaction electron
Thus, back in 1935, materials such as leather, fur, rubber, fibers, detergents, drying oil, varnishes, acetic acid, ethyl alcohol were produced entirely from animal and plant raw materials, including food. Tens of millions of tons of grain, potatoes, fats, raw leather, etc. were spent on this. But already in the 1960s. 100% technical alcohol, 80% detergents, 90% drying oils and varnishes, 40% fibers, 70% rubber and about 25% leather materials were made from gas and oil raw materials. In addition, chemistry annually produces hundreds of thousands of tons of urea and petroleum protein as livestock feed and about 200 million tons of fertilizers.
Such impressive successes have been achieved on the basis of the study of chemical processes - a field of science in which the deepest integration of physics, chemistry and biology has been carried out. This doctrine is based on chemical thermodynamics and kinetics, therefore this section of science belongs equally to physics and chemistry. One of the founders of this scientific direction was the Russian chemist N.N. Semenov is a Nobel Prize laureate, the founder of chemical physics. In his Nobel lecture in 1965, he stated that the chemical process is the fundamental phenomenon that distinguishes chemistry from physics and makes it a more complex science. The chemical process becomes the first step in the ascent from such relatively simple physical objects as an electron, proton, atom, molecule, to complex, multi-level living systems. After all, any cell of a living organism is essentially a kind of complex reactor. Therefore, chemistry becomes a bridge from the objects of physics to the objects of biology.
The study of chemical processes is based on the idea that the ability of various chemical reagents to interact is determined, among other things, by the conditions of chemical reactions. These conditions can affect the nature and results of chemical reactions.
The vast majority of chemical reactions are at the mercy of the elements. Of course, there are reactions that do not require special controls or special conditions. These are the well-known reactions of acid-base interaction (neutralization). However, the vast majority of reactions are difficult to control. There are reactions that simply cannot be carried out, although they are feasible in principle. There are reactions that are difficult to stop: combustion and explosions. And finally, there are reactions that are difficult to introduce into one desired direction, since they spontaneously create dozens of unforeseen branches with the formation of hundreds of by-products. Therefore, the most important task for chemists is the ability to control chemical processes, achieving the desired results.
Methods for controlling chemical processes
In the most general form, methods for controlling chemical processes can be divided into thermodynamic and kinetic.
Thermodynamic methods influence the shift in the chemical equilibrium of a reaction. Kinetic methods affect the rate of a chemical reaction.
The emergence of chemical thermodynamics as an independent direction is usually associated with the appearance in 1884 of the book “Essays on Chemical Dynamics” by the Dutch chemist J. van’t Hoff. It substantiates the laws that establish the dependence of the direction of a chemical reaction on changes in temperature and the thermal effect of the reaction. The energy of chemical processes is closely related to the laws of thermodynamics. Chemical reactions that release energy are called exothermic reactions. In them, energy is released simultaneously with a decrease in the internal energy of the system. There are also endothermic reactions that occur with the absorption of energy. In these reactions, the internal energy of the system increases due to the influx of heat. By measuring the amount of energy released during a reaction (the thermal effect of a chemical reaction), one can judge the change in the internal energy of the system.
At the same time, the French chemist A. Le Chatelier formulated his famous principle of mobile equilibrium, equipping chemists with methods for shifting the equilibrium towards the formation of target products. These control methods are called thermodynamic methods.
Every chemical reaction is in principle reversible, but in practice the equilibrium shifts in one direction or another. This depends both on the nature of the reagents and on the conditions of the process. There are many reactions in which the equilibrium is shifted towards the formation of final products: these include the neutralization reaction, reactions with the removal of finished products in the form of gases or precipitation.
However, there are many chemical reactions in which the equilibrium is shifted to the left, towards the formation of starting substances. To carry them out, special thermodynamic levers are required - an increase in temperature and pressure (if the reaction occurs in the gas phase), as well as the concentration of the reactants (if the reaction occurs in the liquid phase).
Thermodynamic methods primarily influence the direction of chemical processes rather than their rate.
The rate of chemical processes is controlled by chemical kinetics, which studies the dependence of the course of chemical processes on various structural and kinetic factors - the structure of the initial reagents, their concentration, the presence of catalysts and other additives in the reactor, methods of mixing reagents, material and design of the reactor, etc. . The task of studying chemical reactions is very difficult. After all, when solving it, it is necessary to find out the mechanism of interaction not just of two reagents, but also of “third bodies”, of which there may be several. In this case, a step-by-step solution is most appropriate, in which the most powerful effect of one of the “third bodies,” most often a catalyst, is isolated first.
In addition, it should be understood that almost all chemical reactions are by no means a simple interaction of initial reagents, but complex chains of successive stages, where the reagents interact not only with each other, but also with the walls of the reactor, which can both catalyze (accelerate) and inhibit (slow down) the process.
Also, the intensity of chemical processes is influenced by random impurities. Substances of varying degrees of purity manifest themselves in some cases as more active reagents, and in others as inert. Impurities can have both catalytic and inhibitory effects. Therefore, to control the chemical process, certain additives are added to the reacting substances.
Thus, the influence of “third bodies” on the course of chemical reactions can be reduced to catalysis, i.e. a positive effect on a chemical process, or inhibition that restrains the process.
As noted above, the ability of chemical elements to interact is determined not only by their molecular structure, but also by the conditions under which the connection occurs. These conditions influence the outcome of chemical reactions. The greatest impact is experienced by substances with variable composition, in which the connections between individual components are weaker. It is the reaction of such substances that various catalysts have a strong influence on.
Catalysis is the acceleration of a chemical reaction in the presence of special substances - catalysts that interact with reagents, but are not consumed in the reaction and are not part of the final products. Catalysis was discovered in 1812 by the Russian chemist K.S. Kirchhoff. Catalytic processes differ in their physical and chemical nature into the following types:
* heterogeneous catalysis - a chemical reaction of interaction of liquid or gaseous reagents occurs on the surface of a solid catalyst;
* homogeneous catalysis - a chemical reaction occurs either in a gas mixture or in a liquid where both the catalyst and reagents are dissolved;
* electrocatalysis - the reaction occurs on the surface of the electrode in contact with the solution and under the influence of electric current;
* photocatalysis - the reaction occurs on the surface of a solid or in a liquid solution and is stimulated by the energy of absorbed radiation.
Heterogeneous catalysis is the most widespread; it is used to carry out 80% of all catalytic reactions in modern chemistry.
The use of catalysts served as the basis for a radical change in the entire chemical industry. Thanks to them, it became possible to use paraffins and cycloparaffins, hitherto considered “chemical dead”, as raw materials for organic synthesis. Catalysis is necessary in the production of margarine, many food products, and plant protection products. Almost the entire industry of basic chemistry (production of inorganic acids, bases and salts) and “heavy” organic synthesis, including the production of fuels and lubricants, is based on catalysis. Recently, fine organic synthesis has become increasingly catalytic. 60-80% of all chemistry is based on catalytic processes. Chemists, not without reason, say that non-catalytic processes do not exist at all, since they all take place in reactors, the material of the walls of which serves as a kind of catalyst.
For a long time, catalysis itself remained a mystery of nature, giving rise to a wide variety of theories, both purely chemical and physical. These theories, even being erroneous, turned out to be useful, if only because they led scientists to new experiments. The thing is that for most industrially important chemical processes, catalysts were selected through countless trials and errors. So, for example, for the reaction of ammonia synthesis in 1913-1914. German chemists tried more than 20 thousand chemical compounds as catalysts, following the periodic table of elements and combining them in various ways.
Today we can draw some conclusions about the essence of catalysis.
1. Reacting substances come into contact with the catalyst and interact with it, resulting in a weakening of chemical bonds. If a reaction occurs in the absence of a catalyst, then the activation of the molecules of the reacting substances must occur by supplying energy from the outside to the reactor.
2. In the general case, any catalytic reaction can be represented as passing through an intermediate complex in which the redistribution of weakened chemical bonds occurs.
3. In the vast majority of cases, the catalysts are berthollide-type compounds with variable composition, characterized by the presence of weakened chemical bonds or even free valences, which gives them high chemical activity. Molecules of berthollide-type compounds contain a wide range of energetically inhomogeneous bonds or even free atoms on the surface.
4. The consequences of the interaction of reagents with the catalyst are the progress of the reaction in a given direction and an increase in the reaction rate, since the number of meetings of reacting molecules on the surface of the catalyst increases. In addition, the catalyst captures some of the energy of the exothermic reaction to energetically feed all new acts of the reaction and its overall acceleration.
At the present stage of its development, chemistry has discovered many effective catalysts. Among them are ion exchange resins, organometallic compounds, and membrane catalysts. Many chemical elements of the periodic table have catalytic properties, but the most important role is played by the platinum group metals and rare earth metals.
With the participation of catalysts, the rate of some reactions increases by 10 billion times. There are catalysts that not only allow you to control the composition of the final product, but also promote the formation of molecules of a certain shape, which greatly affects the physical properties of the product (hardness, plasticity).
Direction of development of the doctrine of chemical processes
In modern conditions, one of the most important directions in the development of the study of chemical processes is the creation of methods for controlling these processes, therefore chemical science is engaged in the development of such problems as plasma chemistry, radiation chemistry, chemistry of high pressures and temperatures.
Plasma chemistry
Plasma chemistry studies the chemical processes in low-temperature plasma at temperatures from 1000 to 10,000°C. Such processes are characterized by the excited state of particles, collisions of molecules with charged particles, and very high rates of chemical reactions. In plasma-chemical processes, the rate of redistribution of chemical bonds is very high: the duration of elementary acts of chemical transformations is about 10-13 s with almost complete absence of reaction reversibility. The speed of similar chemical processes in conventional reactors is reduced thousands of times due to reversibility. Therefore, plasma-chemical processes are very productive. For example, the productivity of a methane plasma-chemical reactor (its dimensions: length - 65 cm, diameter - 15 cm) is 75 tons of acetylene per day. In this reactor, at a temperature of 3000-3500°C, about 80% of methane is converted into acetylene in one ten-thousandth of a second.
Plasma chemistry has recently been increasingly introduced into industrial production. Technologies for the production of raw materials for powder metallurgy have already been created, and synthesis methods have been developed for a number of chemical compounds. In the 1970s Plasma steel-smelting furnaces were created to produce the highest quality metals. Methods have been developed for ion-plasma treatment of the surface of tools, the wear resistance of which increases several times.
Plasma chemistry makes it possible to synthesize previously unknown materials, such as metal concrete, in which various metals are used as a binding element. Metal concrete is formed by fusing rock particles and firmly compressing them with metal. Its qualities are tens and hundreds of times superior to ordinary concrete.
Radiation chemistry
One of the youngest areas in the study of chemical processes is radiation chemistry, which originated in the second half of the 20th century. The subject of her research was the transformation of a wide variety of substances under the influence of ionizing radiation. Sources of ionizing radiation include X-ray machines, charged particle accelerators, nuclear reactors, and radioactive isotopes. As a result of radiation-chemical reactions, substances obtain increased heat resistance and hardness.
The most important processes of radiation-chemical technology are polymerization, vulcanization, production of composite materials, including the production of polymer concrete by impregnating ordinary concrete with any polymer and then irradiating it. Such concretes have four times higher strength, are waterproof and highly corrosion resistant.
Chemistry of high pressures and temperatures
A fundamentally new and extremely important area of the study of chemical processes is the self-propagating high-temperature synthesis of refractory and ceramic materials. Typically, their production is carried out by the powder metallurgy method, the essence of which is the pressing and compression of metal powders at high temperatures (1200-2000°C). The propagating synthesis itself is much simpler: it is based on the combustion of one metal in another or the combustion of a metal in nitrogen, carbon, silicon, etc.
It has long been known that the combustion process is a combination of oxygen with a combustible substance, therefore combustion is an oxidation reaction of a combustible substance. In this case, electrons move from the atoms of the oxidized substance to the oxygen atoms. From this point of view, combustion is possible not only in oxygen, but also in other oxidizing agents. Self-propagating high-temperature synthesis, the thermal process of combustion in solids, is based on this conclusion. It represents, for example, the combustion of titanium powder in boron powder, or zirconium powder in silicon powder. As a result of this synthesis, hundreds of refractory compounds of the highest quality are obtained.
It is very important that this technology does not require cumbersome processes, is highly technological and can be easily automated.
High pressure chemistry
Another area of development of the study of chemical processes is the chemistry of high and ultra-high pressures. Chemical transformations of substances at pressures above 100 atm belong to high pressure chemistry, and at pressures above 1000 atm - to ultra-high pressure chemistry. High pressures have been used in chemistry since the beginning of the 20th century. -- ammonia production was carried out at a pressure of 300 atm and a temperature of 600°C. But recently, installations have been used in which a pressure of 5000 atm is achieved, and tests are carried out at a pressure of 600,000 atm, which is achieved due to the shock wave of the explosion within a millionth of a second. Nuclear explosions produce even higher pressures.
At high pressure, the electron shells of atoms come closer together and are deformed, which leads to an increase in the reactivity of substances. At a pressure of 102-103 atm, the difference between the liquid and gas phases disappears, and at 103-105 atm, between the solid and liquid phases. At high pressure, the physical and chemical properties of substances change greatly. For example, at a pressure of 20,000 atm, the metal becomes elastic, like rubber. Ordinary water becomes chemically active at high temperatures and pressures. With increasing pressure, many substances transform into a metallic state. Thus, in 1973, scientists observed metallic hydrogen at a pressure of 2.8 million atm.
One of the most important achievements of ultra-high pressure chemistry was the synthesis of diamonds. It runs at a pressure of 50,000 atm and a temperature of 2000°C. In this case, graphite crystallizes into diamonds. Diamonds can also be synthesized using shock waves. Recently, tons of synthetic diamonds are produced annually, which differ only slightly from natural ones in their properties. The resulting diamonds are used for industrial purposes - in cutting and drilling equipment. It was possible to synthesize black diamonds - carbonados, which are harder than natural diamonds. They are used to process the diamonds themselves.
Currently, industrial production has been established not only of artificial diamonds, but also of other precious stones - corundum (red ruby), emerald, etc. Other materials that are highly heat resistant are also synthesized at high pressures. Thus, boron nitride was synthesized from boron nitride at a pressure of 100,000 atm and a temperature of 2000°C - a material suitable for drilling and grinding parts made of extremely hard materials at very high temperatures.
Energy of chemical processes and systems
Chemical reactions are interactions between atoms and molecules, leading to the formation of new substances that differ from the original ones in chemical composition or structure. Chemical reactions, unlike nuclear reactions, do not change either the total number of atoms in the system or the isotopic composition of the elements.
A system is a collection of bodies isolated from space. If a system allows mass and heat exchange between all its components, then such a system is called thermodynamic. A chemical system in which reactions can occur is a special case of a thermodynamic system. If there is no mass and heat transfer between the system and the environment, then such a system is called isolated. If there is no mass transfer, but heat exchange is possible, then the system is called closed. If both mass and heat exchange are possible between the system and the environment, then the system is open. A system consisting of several phases is called heterogeneous, a single-phase system is called homogeneous.
The state of a chemical system is determined by its properties: temperature, pressure, concentration, volume, energy.
Reactions occurring in a homogeneous system develop throughout its entire volume and are called homogeneous. Reactions occurring at the interface are heterogeneous.
For a thermodynamic description of a system, the so-called system state functions are used - this is any physical quantity whose values are uniquely determined by the thermodynamic properties of the system. The most important functions of the system state include:
Total energy of the system (E);
Internal energy of the system (U);
Enthalpy (or heat content) is a measure of the energy accumulated by a substance during its formation (H):
Entropy is a measure of the disorder of a system (S);
Gibbs energy is a measure of the stability of a system at constant pressure (G):
Helmholtz energy is a measure of the stability of a system at constant volume (F):
The possibility of a spontaneous process can be judged by the sign of the change in the Gibbs free energy function: if?G< 0, т.е. в процессе взаимодействия происходит уменьшение свободной энергии, то процесс термодинамически возможен. Если?G >0, then the process is impossible. Thus, all processes can spontaneously proceed in the direction of decreasing free energy.
Chemical interaction is usually accompanied by a thermal effect. Processes that occur with the release of heat are called exothermic (?H< 0), а идущие с поглощением теплоты - эндотермическими (?Н > 0).
The thermal effect of chemical processes under isobaric conditions is determined by the change in enthalpy, i.e. the difference between the enthalpies of the final and initial states. According to the Lavoisier-Laplace law: the heat released during the formation of a substance is equal to the heat absorbed during the decomposition of the same amount of it into its original components.
Deeper generalizations of thermochemical laws are given by Hess's law: the thermal effect of chemical reactions occurring either at constant pressure or at constant volume does not depend on the number of intermediate stages, but is determined only by the initial and final states of the system.
First law of thermodynamics (law of conservation of energy) - energy does not disappear and does not appear again from nothing during a process, it can only pass from one form to another in strictly equivalent relationships.
II law of thermodynamics - when a process occurs in an isolated system of reversible processes, entropy remains unchanged, but during irreversible processes it increases. .
Conclusion
Chemistry is a social science. Its highest goal is to satisfy the needs of each person and the entire society. Many of humanity's hopes turn to chemistry. Molecular biology, genetic engineering and biotechnology, and materials science are fundamentally chemical sciences. The progress of medicine and health care is the problems of the chemistry of diseases, medicines, food; neurophysiology and brain function are, first of all, neurochemistry, chemistry, and the chemistry of memory. Humanity expects from chemistry new materials with magical properties, new energy sources and batteries, new clean and safe technologies, etc.
As a fundamental science, chemistry was formed at the beginning of the 20th century, together with the new, quantum mechanics. And this is an indisputable truth, because all objects of chemistry are atoms, molecules, ions, etc. - are quantum objects. The main events in chemistry are chemical reactions and chemical processes i.e. The rearrangement of atomic nuclei and the transformation of electron shells, electronic clothes of reactant molecules into product molecules is also a quantum event.
The need for chemical processes arises under the influence of new production requirements. Methods for solving the main problem of chemistry based on the doctrine of composition and structural theories studied earlier were clearly not sufficient here and a new level arises - the level of chemical knowledge - knowledge about chemical processes. Chemistry is becoming a science not only and not so much of substances as complete objects, but a science of processes and mechanisms of change in matter. Thanks to this, it ensured the production of synthetic materials.
In modern society, the study of chemical processes is necessary knowledge, since science needs to develop and strive for new discoveries, and only man can contribute to this.
List of used literature
1. Bochkarev A. I. - Concepts of modern natural science: a textbook for university students A. I. Bochkarev, T. S. Bochkareva, S. V. Saksonov; edited by prof. A. I. Bochkareva. - Tolyatti: TGUS, 2008. - 386 p. [electronic resource]www.tolgas.ru (access date 11/14/2102)
2. Sadokhin A.P. Concepts of modern natural science: a textbook for university students studying in the humanities and specialties in economics and management / A.P. Sadokhin. -- 2nd ed., revised. and additional - M.: UNITY-DANA, 2006. - 447 pp. [electronic resource] http://www.twirpx.com/file/20132/ (access date: 12/10/2102)
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test, added 09/15/2013
Order, disorder in nature, features of thermal movement as an example of chaotic, unorganized order. The phenomenon of energy dissipation process. Chemical processes and properties of substances. Quality of bodies in a rocket under high speed conditions.
course work, added 03/11/2010
Study of the theory of self-organization. The main criterion for the development of self-organizing systems. Nonequilibrium processes and open systems. Self-organization of dissipative structures. Chemical reaction of Belousov-Zhabotinsky. Self-organization in physical phenomena.
abstract, added 09/30/2010
The development of the nucleus as one of the structural elements of a eukaryotic cell, which contains genetic information in DNA molecules. Nuclear envelope, nucleus, matrix as structural elements of the nucleus. Characteristics of the processes of replication and transcription of molecules.
presentation, added 01/08/2012
Analysis of the mechanisms of passage of substances through the cell membrane. The main processes by which substances penetrate the membrane. Properties of simple and facilitated diffusion. Types of active transport. Ion channels, their difference from pores, gradient.
presentation, added 11/06/2014
Transformation of nitrogenous substances in plants. The quality of vegetable oils depending on environmental factors. Transformation of substances during the ripening of oilseed seeds. Vernalization, its essence and significance. The influence of temperature and light on seed dormancy.
test, added 09/05/2011
Analysis of possible pathways of glucose breakdown. Determination of the components and principle of functioning of aerobic metabolism. Processes of formation of organic acids and biotransformation of initial substrates that differ from carbohydrates in their chemical nature.
abstract, added 06/09/2015
Flows of matter, energy and destructive blocks in ecosystems. Problems of biological productivity. Pyramids of numbers, biomass and energy. Processes of transformation of matter and energy between biota and the physical environment. Biochemical circulation of substances.
abstract, added 06/26/2010
Newton's law of gravity. Special theory of relativity. Second law of thermodynamics. Ideas about the structure of atoms. Methods of chemical kinetics. Concepts of equilibrium, equilibrium radiation. Nuclear fusion reactions. Features of the biotic cycle.
test, added 04/16/2011
Description of the main functions performed by the processes of secretion of substances in plants. The concept of allelopathy, excretion and secretion. Functions of specialized secretory structures in plants. Groups of epidermal formations involved in the secretion of substances.
Let us not judge the most significant things too quickly.
Heraclitus
Chemical process(from lat. processus- advancement) is a sequential change in states of matter, a close connection between successive stages of development, representing a continuous, unified movement. The study of chemical processes is a field of science in which there is the deepest interpenetration of physics, chemistry and biology. Chemical processes are divided into: homo- And heterogeneous(depending on the state of aggregation of the reacting systems), exo- And endothermic(depending on the amount of heat released and absorbed), oxidizing, reducing(depending on the relationship to oxygen), etc.
All the processes that take place around us can be combined into three large groups.
1. Spontaneous processes that can be used
to produce energy or do work. Terms
the course of spontaneous processes or the laws of thermo
the dynamics characterized by them are: a) in an isolated
system, i.e. in a system for which any material is excluded
nal or energy exchange with the environment, amount
all types of energy are constant; b) change
enthalpy (thermal effect of the process, AH) depends only on
type and state of starting substances and products and does not depend
from the transition path. It is called Hess's law and is formulated
founded by him in 1840
2. Processes that require costs
energy or work done.
3. Self-organization of a chemical system, i.e. self-production
a free process that takes place without changing the energy
system reserve, occurs only in the direction in which
order in the system increases, i.e. where entropy decreases.
The ability of various chemical reagents to interact is determined not only by their atomic-molecular structure, but also by the conditions under which chemical reactions occur. The process of converting one substance into another is called a chemical reaction. The conditions for the occurrence of chemical processes include, first of all, thermodynamic factors that characterize the dependence of reactions on temperature, pressure and some other conditions. The rate of a chemical reaction is also affected by the following conditions and parameters:
1) nature reacting substances (for example, alkali metals dissolve in water with the formation of alkalis and the release of hydrogen, and the reaction proceeds instantly under normal conditions, while zinc, iron and others react slowly and form oxides, and noble metals do not react at all);
2) temperature. For every 10 °C increase in temperature, the reaction rate increases by 2-4 times (van't Hoff's rule). Oxygen begins to react with many substances at a noticeable speed already at ordinary temperatures (slow oxidation). As the temperature rises, a violent reaction (combustion) begins;
3) concentration. For dissolved substances and gases, the rate of chemical reactions depends on the concentration of the reacting substances. Combustion of substances in pure oxygen occurs more intensely than in air, where the oxygen concentration is almost 5 times less. The law of mass action is valid here: at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the concentration of the reacting substances;
4) reaction surface area. For substances in the solid state, the rate is directly proportional to the surface area of the reacting substances. Iron and sulfur in the solid state react quickly enough only with preliminary grinding and mixing: burning brushwood and logs;
5) catalyst. The speed of a reaction depends on catalysts, substances that speed up chemical reactions without being consumed. The decomposition of berthollet salt and hydrogen peroxide is accelerated in the presence of manganese (IV) oxide, etc.
To enter into a chemical reaction, it is necessary to overcome a certain energy barrier corresponding to the activation energy, the possibility of accumulation of which strongly depends on temperature. Many reactions cannot end for a long time. In this case, the reaction is said to have reached chemical equilibrium. A chemical system is in a state of equilibrium if the following three conditions are met:
1) no energy changes occur in the system (H = 0);
2) there is no change in the degree of disorder (, S = 0);
3) the isobaric potential does not change (J = 0).
Van't Toff, using a thermodynamic approach, classified chemical reactions and also formulated the basic principles of chemical kinetics. Chemical kinetics studies the rates of chemical reactions. Le Chatelier formulated the law of displacement of chemical equilibrium in chemical reactions under the influence of external factors - temperature, pressure, etc. According to Le Chatelier’s principle, if a system in a state of chemical equilibrium is subject to an external influence (temperature, pressure or concentration changes), then the position the equilibrium of the chemical reaction shifts in the direction that weakens this effect.
Chemical reactions are classified according to changes in the quality of the starting substances and reaction products into the following types:
connection reactions- reactions in which several substances form one substance, more complex than the original ones;
decomposition reactions- reactions in which several substances are formed from one complex substance;
substitution reactions- reactions in which atoms of one element replace an atom of another element in a complex substance and at the same time two new ones are formed - simple and complex;
exchange reactions- reactions in which reacting substances exchange their constituent parts, resulting in
from which two complex substances are formed into two new complex substances.
According to the thermal effect, chemical reactions can be divided into exothermic- with the release of heat and endothermic- with heat absorption. Taking into account the phenomenon of catalysis, reactions can be catalytic- using catalysts and non-catalytic- without the use of catalysts. Based on reversibility, reactions are divided into reversible And irreversible.
IN. Ostwald, studying the conditions of chemical equilibrium, came to the discovery of the phenomenon of catalysis. It turned out that to a large extent the nature and especially the rate of reactions depend on kinetic conditions, which are determined by the presence of catalysts and other additives to the reagents, as well as the influence of solvents, reactor walls and other conditions. Phenomenon catalysis- selective acceleration of chemical processes in the presence of substances (catalysts) that take part in intermediate processes but are regenerated at the end of the reaction, widely used in industry, for example, nitrogen and hydrogen fixation, contact method for the production of sulfuric acid and many others. The synthesis of ammonia was first carried out in 1918 based on the work of Haber, K. Bosch and A. Mittash using a catalyst consisting of metallic iron with the addition of potassium and aluminum oxides, at a temperature of 450-550 °C and a pressure of 300-1000 atmospheres. Currently, much attention is paid to the use of organometallic and metal-complex catalysts, characterized by high selectivity and selective action. The same process of ammonia synthesis using an organometallic catalyst was possible to carry out at normal temperature (18 °C) and normal atmospheric pressure, which opens up great prospects in the production of mineral nitrogen fertilizers. The role of catalysis is especially important in organic synthesis. The greatest success in this direction must be recognized as the production of artificial synthetic rubber from ethyl alcohol, carried out by Soviet academician S.V. Lebedev in the 20s of the 20th century.
Enzymes, or biocatalysts, play an exceptional role in biological processes and the technology of substances of plant and animal origin, as well as in medicine. Currently, over 750 enzymes are known, and their number is increasing every year. Enzymes are bifunctional and polyfunctional catalysts, since here there is a coordinated effect of two or several groups of catalysts of different nature in the active center of the enzyme on the polarization of certain substrate bonds. The same concept underlies the catalytic action of the enzyme and the theory of the kinetics of enzyme action. The main difference between enzymes and other catalysts is their exceptionally high activity and pronounced specificity.
The self-organization of chemical systems into biological ones, their unity and interconnection confirms the synthesis of organic compounds from inorganic ones. In 1824, the German chemist F. Wöhler, a student of Berzelius, first obtained oxalic acid HOOC-COOH, an organic compound, from inorganic cyanogen N-C-C-N by heating it with water. A new organic substance was also obtained - urea (carbamide) from ammonium cyanide. In 1854 in France, M. Berthelot obtained fat synthetically. The greatest success of chemistry was in the 50s and 60s. XX century was the first synthesis of simple proteins - the hormone insulin and the enzyme ribonucleosis.
Let us not judge the most significant things too quickly.
Heraclitus
Chemical process (lat.“processus” - advancement) represents a consistent change in states of matter, a close connection between successive stages of development, representing a continuous unified movement. The study of chemical processes is an area of science in which there is the deepest interpenetration of the physics of chemistry and biology. Chemical processes are divided into homo- and heterogeneous (depending on the state of aggregation of the reacting systems), exo- and endothermic (depending on the amount of heat released and absorbed), oxidative, reduction (depending on the relationship to oxygen), etc.
All processes can be combined into three large groups:
- 1. Spontaneous processes that can be used to obtain energy or do work. The conditions for the occurrence of spontaneous processes are: a) in an isolated system, i.e. in a system for which any material or energy exchange with the environment is excluded, the sum of all types of energy is a constant value; b) the change in enthalpy (thermal effect of the process, DP) depends only on the type and state of the starting substances and products and does not depend on the transition path. This dependence is called Hess’s law, formulated by Hess in 1840.
- 2. Processes that require the expenditure of energy or work.
- 3. Self-organization of a chemical system, i.e. a spontaneous process that takes place without changing the energy reserve of the system occurs only in the direction in which the order in the system decreases, i.e. where disorder increases (D5 > 0).
The ability of various chemical reagents to interact is determined not only by their atomic-molecular structure, but also by the conditions under which chemical reactions occur. The process of transforming one substance into another is called a chemical reaction. The conditions for the occurrence of chemical processes include, first of all, thermodynamic factors that characterize the dependence of reactions on temperature, pressure and some other conditions. The speed of a chemical reaction is also affected by the following conditions and parameters:
- 1) the nature of the reacting substances (for example, alkali metals dissolve in water with the formation of alkalis and the release of hydrogen, and the reaction proceeds instantly under normal conditions; zinc, iron and others react slowly and form oxides, and noble metals do not react at all);
- 2) temperature (for every 10 °C increase in temperature, the reaction rate increases by 2-4 times - van’t Hoff’s rule). Oxygen begins to react with many substances at a noticeable speed already at ordinary temperatures (slow oxidation). As the temperature rises, a violent reaction (combustion) begins;
- 3) concentration (for substances in a dissolved state and gases, the rate of chemical reactions depends on the concentration of the reacting substances. The combustion of substances in pure oxygen occurs more intensely than in air, where the oxygen concentration is almost 5 times less). Here the law of mass action is valid: at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the concentration of the reacting substances;
- 4) reaction surface area (for substances in the solid state - the speed is directly proportional to the surface of the reacting substances. Iron and sulfur in the solid state react quickly enough only with preliminary grinding and mixing: burning brushwood and logs);
- 5) catalyst (the reaction rate depends on catalysts, substances that accelerate chemical reactions, but are not consumed themselves. The decomposition of berthollet salt and hydrogen peroxide is accelerated in the presence of manganese (IV) oxide, etc.).
To enter into a chemical reaction, it is necessary to overcome a certain energy barrier corresponding to the activation energy, the possibility of accumulation of which strongly depends on temperature. Many reactions cannot end for a long time. In this case, the reaction is said to have reached chemical equilibrium. A chemical system is in a state of equilibrium if the following three conditions are met:
- 1) no energy changes occur in the system (AN = 0);
- 2) there is no change in the degree of disorder (AS = 0);
- 3) the isobaric potential does not change (A/ = 0).
Van't Hoff, using a thermodynamic approach, classified chemical reactions and also formulated the basic principles of chemical kinetics. Chemical kinetics studies the rates of chemical reactions. Le Chatelier formulated the law of displacement of chemical equilibrium in chemical reactions under the influence of external factors - temperature, pressure, etc. According to Le Chatelier's principle: if an external influence is exerted on a system in a state of chemical equilibrium (temperature, pressure, or concentration changes), then the equilibrium position chemical reaction shifts in the direction that weakens this effect.
Chemical reactions are classified according to changes in the quality of the starting substances and reaction products into the following types:
- - reactions connections- reactions in which several substances form one substance, more complex than the original ones;
- - decompositions - reactions in which several substances are formed from one complex substance;
- - substitution- reactions in which atoms of one element replace an atom of another element in a complex substance and at the same time two new ones are formed - simple and complex;
- - exchange - reactions in which reacting substances exchange their constituent parts, resulting in the formation of two new complex substances from two complex substances.
According to the thermal effect, chemical reactions can be divided into exothermic - with the release of heat and endothermic - with heat absorption. Taking into account the phenomenon of catalysis, reactions can be catalytic - using catalysts and iecatalytic - no use of catalysts. Based on the reversibility of the reaction, dividing by reversible And irreversible.
Ostwald, studying the conditions of chemical equilibrium, came to the discovery of the phenomenon of catalysis. It turned out that to a large extent the nature and especially the rate of reactions depend on kinetic conditions, which are determined by the presence of catalysts and other additives to the reagents, as well as the influence of solvents, reactor walls and other conditions. The phenomenon of catalysis - the selective acceleration of chemical processes in the presence of substances (catalysts) that take part in intermediate processes but are regenerated at the end of the reaction - is widely used in industry. For example, the industrial production of ammonia, the contact method for the production of sulfuric acid and many others. The synthesis of ammonia was first carried out in 1918 based on the work of Haber, Bosch and Mittash using a catalyst consisting of metallic iron with the addition of potassium and aluminum oxides, at a temperature of 450-550 ° C and a pressure of 300-1000 atm. Currently, much attention is paid to the use of organometallic and metal-complex catalysts, which are characterized by high selectivity and selective action. The same process of ammonia synthesis using a metal organic catalyst was possible to carry out at normal temperature (18 ° C) and normal atmospheric pressure, which opens up great prospects in the production of mineral nitrogen fertilizers. The role of catalysis in organic synthesis is especially great. The greatest success in this direction must be recognized as the production of artificial and synthetic rubber from ethyl alcohol, carried out by Soviet academician S.V. Lebedev in the 20s. XX century
Enzymes, or biocatalysts, play an exceptional role in biological processes and in the technology of substances of plant and animal origin, as well as in medicine. Today, over 750 enzymes are known, and their number increases every year. Enzymes are bifunctional and polyfunctional catalysts, since here there is a coordinated effect of two or several groups of catalysts of different nature in the active center of the enzyme on the polarization of certain substrate bonds. The same concept underlies the catalytic action of the enzyme and the theory of the kinetics of enzyme action. The main difference between enzymes and other catalysts is their exceptionally high activity and pronounced specificity.
The self-organization of chemical systems into biological ones, their unity and interconnection confirms the synthesis of organic compounds from inorganic ones. In 1824, the German chemist F. Wöhler, a student of Berzelius, was the first to obtain oxalic acid HOOC-COOH, an organic compound, from inorganic cyanogen MCCA by heating it with water. In the same way, a new organic substance, urea (urea), was obtained from ammonium cyanide. In 1854 in France, M. Berthelot obtained fat synthetically. The greatest success of chemistry was in the 50-60s. XX century was the first synthesis of simple proteins - the hormone insulin and the enzyme ribonuclease.
The mutual transformations of compounds observed in living nature, as well as those occurring as a result of human activity, can be considered as chemical processes. The reagents in them can be either two or more substances located in the same or different states of aggregation. Depending on this, homogeneous or heterogeneous systems are distinguished. The conditions, features of the course and the role of chemical processes in nature will be discussed in this work.
What is meant by a chemical reaction?
If, as a result of the interaction of the starting substances, the constituent parts of their molecules undergo changes, but the charges of the atomic nuclei remain the same, we speak of chemical reactions or processes. The products formed as a result of their flow are used by humans in industry, agriculture and everyday life. A huge number of interactions between substances occur in both living and inanimate nature. Chemical processes are fundamentally different from physical phenomena and the properties of radioactivity. Molecules of new substances are formed in them, while physical processes do not change the composition of the compounds, and atoms of new chemical elements appear in nuclear reactions.
Conditions for carrying out processes in chemistry
They can be different and depend, first of all, on the nature of the reagents, the need for an influx of energy from the outside, as well as the state of aggregation (solids, solutions, gases) in which the process occurs. The chemical mechanism of interaction between two or more compounds can be carried out under the influence of catalysts (for example, the production of nitric acid), temperature (production of ammonia), or light energy (photosynthesis). With the participation of enzymes in living nature, the processes of chemical fermentation reactions (alcoholic, lactic acid, butyric acid) are widespread, used in the food and microbiological industries. To obtain products in the organic synthesis industry, one of the main conditions is the presence of a free radical mechanism of the chemical process. An example would be the production of chlorinated derivatives of methane (dichloromethane, trichloromethane, carbon tetrachloride, formed as a result of chain reactions.
Homogeneous catalysis
They represent special types of contact between two or more substances. The essence of chemical processes occurring in a homogeneous phase (for example, gas - gas) with the participation of reaction accelerators is to carry out reactions in the entire volume of mixtures. If the catalyst is in the same state of aggregation as the reagents, it forms mobile intermediate complexes with the starting compounds.
Homogeneous catalysis is a basic chemical process carried out, for example, in oil refining, the production of gasoline, naphtha, gas oil, and other types of fuel. It uses technologies such as reforming, isomerization, and catalytic cracking.
Heterogeneous catalysis
In the case of heterogeneous catalysis, the contact of the reacting substances occurs, most often, on the solid surface of the catalyst itself. So-called active centers are formed on it. These are areas where the interaction of reacting compounds occurs very quickly, that is, it is high. They are species-specific and also play an important role if chemical processes occur in living cells. Then they talk about metabolism - metabolic reactions. An example of heterogeneous catalysis is the industrial production of sulfate acid. In a contact apparatus, a gaseous mixture of sulfur dioxide and oxygen is heated and passed through grid shelves filled with dispersed powder of vanadium oxide or vanadyl sulfate VOSO 4. The resulting product, sulfur trioxide, is then absorbed into concentrated sulfuric acid. A liquid called oleum is formed. It can be diluted with water to obtain sulfate acid of the desired concentration.
Features of thermochemical reactions
The release or absorption of energy in the form of heat is of great practical importance. Suffice it to recall the combustion reactions of fuels: natural gas, coal, peat. They represent physical and chemical processes, an important characteristic of which is the heat of combustion. Thermal reactions are widespread both in the organic world and in inanimate nature. For example, during the digestion process, proteins, lipids and carbohydrates are broken down under the action of biologically active substances - enzymes.
The released energy is accumulated in the form of ATP molecules. Dissimilation reactions are accompanied by the release of energy, part of which is dissipated in the form of heat. As a result of digestion, each gram of protein provides 17.2 kJ of energy, starch - 17.2 kJ, fat - 38.9 kJ. Chemical processes that release energy are called exothermic, and those that absorb energy are called endothermic. In the organic synthesis industry and other technologies, the thermal effects of thermochemical reactions are calculated. This is important to know, for example, to correctly calculate the amount of energy used to heat reactors and synthesis columns in which reactions occur that involve the absorption of heat.
Kinetics and its role in the theory of chemical processes
Calculating the speed of reacting particles (molecules, ions) is the most important task facing industry. Its solution provides an economic effect and profitability of technological cycles in chemical production. To increase the speed of such a reaction, such as the synthesis of ammonia, the decisive factors will be changing the pressure in the gas mixture of nitrogen and hydrogen to 30 MPa, as well as preventing a sharp increase in temperature (the optimal temperature is 450-550 ° C).
The chemical processes used in the production of sulfate acid, namely: burning of pyrites, oxidation of sulfur dioxide, absorption of sulfur trioxide by oleum, are carried out under various conditions. For this purpose, a pyrite furnace and contact devices are used. They take into account the concentrations of reacting substances, temperature and pressure. All these factors are correlated to carry out the reaction at the highest speed, which increases the yield of sulfate acid to 96-98%.
The cycle of substances as physical and chemical processes in nature
The well-known saying “Movement is life” can also be applied to chemical elements that enter into various types of interactions (reactions of combination, substitution, decomposition, exchange). Molecules and atoms of chemical elements are in continuous motion. As scientists have established, all of the above can be accompanied by physical phenomena: the release of heat or its absorption, the emission of photons of light, a change in the state of aggregation. These processes occur in every shell of the Earth: lithosphere, hydrosphere, atmosphere, biosphere. The most significant of them are the cycles of substances such as oxygen, carbon dioxide and nitrogen. In the next title we will look at how nitrogen circulates in the atmosphere, soil and living organisms.
Interconversion of nitrogen and its compounds
It is well known that nitrogen is a necessary component of proteins, and therefore participates in the formation of all types of terrestrial life without exception. Nitrogen is absorbed by plants and animals in the form of ions: ammonium, nitrate and nitrite ions. As a result of photosynthesis, plants produce not only glucose, but also amino acids, glycerol, and fatty acids. All of the above chemical compounds are products of reactions occurring in the Calvin cycle. The outstanding Russian scientist K. Timiryazev spoke about the cosmic role of green plants, meaning, among other things, their ability to synthesize proteins.
Herbivores obtain peptides from plant foods, while carnivores obtain peptides from the meat of prey. During the decay of plant and animal remains under the influence of saprotrophic soil bacteria, complex biological and chemical processes occur. As a result, nitrogen from organic compounds is converted into inorganic form (ammonia, free nitrogen, nitrates and nitrites are formed). Returning to the atmosphere and soil, all these substances are again absorbed by plants. Nitrogen enters through the stomata of the leaf skin, and solutions of nitrogen and their salts are absorbed by the root hairs of plant roots. The nitrogen conversion cycle closes to repeat itself. The essence of chemical processes occurring in nature was studied in detail at the beginning of the 20th century by the Russian scientist D.N. Pryanishnikov.
Powder metallurgy
Modern chemical processes and technologies make a significant contribution to the creation of materials with unique physical and chemical properties. This is especially important, first of all, for instruments and equipment of oil refineries, enterprises producing inorganic acids, dyes, varnishes, and plastics. In their production, heat exchangers, contact devices, synthesis columns, and pipelines are used. The surface of the equipment comes into contact with aggressive media under high pressure. Moreover, almost all chemical production processes are carried out at high temperatures. It is urgent to obtain materials with high levels of heat and acid resistance and anti-corrosion properties.
Powder metallurgy includes the processes of producing metal-containing powders, sintering and introducing into the composition of modern alloys used in reactions with chemically aggressive substances.
Composites and their meaning
Among modern technologies, the most important chemical processes are reactions for the production of composite materials. These include foams, cermets, and norpapalsts. Metals and their alloys, ceramics, and plastics are used as a matrix for production. Calcium silicate, white clay, strontium and barium ferrides are used as fillers. All of the above substances give composite materials impact resistance, heat resistance and wear resistance.
What is chemical technology
The branch of science involved in the study of means and methods used in the reactions of processing raw materials: oil, natural gas, coal, minerals, was called chemical technology. In other words, it is the science of chemical processes occurring as a result of human activity. Its entire theoretical base consists of mathematics, cybernetics, physical chemistry, and industrial economics. It doesn’t matter what chemical process is involved in the technology (production of nitrate acid, decomposition of limestone, synthesis of phenol-formaldehyde plastics) - in modern conditions it is impossible without automated control systems that facilitate human activity, eliminate environmental pollution, and ensure continuous and waste-free chemical production technology.
In this work, we looked at examples of chemical processes occurring both in living nature (photosynthesis, dissimilation, nitrogen cycle) and in industry.
