All chemical processes. Chemical processes
41. Definition of solution. Physical and chemical processes during the formation of solutions. Change in enthalpy and entropy during dissolution.
A solution is a homogeneous system consisting of two or more components (components), the relative amounts of which can vary over a wide range. Any solution consists of solutes and a solvent, i.e. environment in which these substances are evenly distributed in the form of molecules or ions. Usually, a solvent is considered to be that component that exists in its pure form in the same state of aggregation as the resulting solution. If both components before dissolution were in the same state of aggregation, then the solvent is considered to be the component in a larger amount. A solution in equilibrium with a solute is called a saturated solution. Unsaturated solutions with a low content of solute - dilute; with high - concentrated.
1. Thermal effect of dissolution. Depending on the nature of the substances, the dissolution is accompanied by the release (KOH) or absorption (NH4NO3) of heat. 2. Volume change 3. Solution color change
The change in enthalpy and entropy during dissolution: dissolution is considered as a set of physical and chemical phenomena, highlighting 3 main processes: 1. Destruction of chemical and intermolecular bonds in dissolving substances, which requires energy (enthalpy increases). 2. Chemical interaction of the solvent with the solute, energy release (enthalpy decreases). 3. Spontaneous mixing of the solution associated with diffusion and requiring energy. When liquid and solid substances are dissolved, the entropy of the system usually increases, since the dissolved substances pass from a more ordered state to a less ordered one. When gases dissolve in liquids, entropy decreases as the solute moves from a larger volume to a smaller one.
42. Methods for expressing the concentration of solutions.
Concentration is the amount of a substance per unit mass of a solution or solvent.
Mass fraction - the ratio of the mass of the solute to the mass of the solution. w=(mb/m)*100%
Volume fraction - the ratio of the volume of a substance to the volume of the entire solution
Mole fraction - the ratio of the amount of a solute to the sum of the amounts of all substances that make up the solution. w=nb/(na+nb) nb=mb/µb
Molar concentration (molarity) - the ratio of the amount of solute to the volume of the solution. w=nb/V
Molar concentration (molality) - the ratio of the amount of a solute to the mass of the solvent. w=nb/ma
The molar concentration of equivalents is the ratio of the number of equivalents of a solute to the volume of a solution. w=ne/V
43. Raoult's Law
At a given temperature, the saturation vapor pressure over each liquid is a constant value. Experience shows that when a substance is dissolved in a liquid, the saturated vapor pressure of this liquid decreases. Thus, the saturation vapor pressure of a solvent over a solution is always lower than over a pure solvent at the same temperature. The difference between these values is usually called the decrease in vapor pressure over the solution. The ratio of the magnitude of this decrease to the saturation vapor pressure over the pure solvent is called the relative decrease in vapor pressure over the solution. Raoult's Law: The relative reduction in saturation vapor pressure of a solvent over a solution is equal to the mole fraction of the solute. The phenomenon of a decrease in the pressure of saturated vapor over a solution follows from the Le Chatelier principle. Initially, liquid and vapor are in equilibrium. When a substance dissolves in a liquid, the concentration of solvent molecules decreases. The system seeks to compensate for this impact. Steam condensation begins and a new equilibrium is established at a lower saturated vapor pressure.
Let's not judge the most important things too quickly.
Heraclitus
chemical process (lat."processus" - promotion) is a successive change of states of matter, a close connection of successive stages of development, representing a continuous single movement. The doctrine 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), exothermic and endothermic (depending on the amount of released and absorbed heat), oxidative, reducing (depending on the ratio to oxygen), etc.
All processes can be grouped into three large groups:
- 1. Spontaneous processes that can be used to generate 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 (the thermal effect of the process, DP) depends only on the type and state of the starting materials and products and does not depend on the transition path. This dependence is called Hess' law, formulated by Hess in 1840.
- 2. Processes for the implementation of which the expenditure of energy or the performance of work is required.
- 3. Self-organization of a chemical system, i.e. a spontaneous process that takes place without changing the energy reserve of the system takes place only in the direction in which the order in the system decreases, i.e. where the disorder increases (A5 > 0).
The ability to interact with various chemical reagents is determined not only by their atomic and molecular structure, but also by the conditions for the occurrence of chemical reactions. The process of changing one substance into another is called a chemical reaction. The conditions for the flow of chemical processes include, first of all, thermodynamic factors characterizing the dependence of reactions on temperature, pressure, and some other conditions. The following conditions and parameters also affect the rate of a chemical reaction:
- 1) the nature of the reactants (for example, alkali metals dissolve in water with the formation of alkalis and the evolution 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 (with an increase in temperature for every 10 ° C, the reaction rate increases by 2-4 times - the van't Hoff rule). With many substances, oxygen begins to react at a noticeable rate even at ordinary temperatures (slow oxidation). When 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 reactants;
- 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) a catalyst (the reaction rate depends on catalysts, substances that accelerate chemical reactions, but are not consumed by 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 take a long time to complete. In this case, the reaction is said to have reached chemical equilibrium. A chemical system is in equilibrium if the following three conditions are met:
- 1) there are no energy changes in the system (AH = 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 the thermodynamic approach, classified chemical reactions, and also formulated the basic provisions of chemical kinetics. Chemical kinetics studies the rates of chemical reactions. Le Chatelier formulated the law of shifting 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 chemical equilibrium (temperature, pressure or concentration changes), then the equilibrium position the chemical reaction is shifted in the direction that weakens this effect.
Chemical reactions are classified according to the change in the quality of the starting materials and reaction products into the following types:
- - reactions connections- reactions in which one substance is formed from several substances, more complex than the original ones;
- - decomposition - 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 reactants exchange their constituents, as a result of which two new complex substances are formed 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 - without the use of catalysts. On the basis of the reversibility of the reaction, dividing by reversible and irreversible.
Ostwald, investigating 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 the 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. Ammonia was first synthesized in 1918 on the basis of the work of Haber, Bosch and Mittash using a catalyst, which is metallic iron with the addition of potassium and aluminum oxides, at a temperature of 450-550 ° C and a pressure of 300-1000 atm. At present, much attention is paid to the use of organometallic and metal complex catalysts, which are distinguished by high selectivity and selectivity of action. The same process of ammonia synthesis using a metal-organic catalyst was successfully carried out at the usual 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 the Soviet academician S. V. Lebedev in the 1920s. 20th 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 is increasing every year. Enzymes are bifunctional and polyfunctional catalysts, since here there is a coordinated effect of two or more 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 an enzyme and the theory of the kinetics of enzyme action. The main difference between enzymes and other catalysts lies in their exceptionally high activity and pronounced specificity.
Self-organization of chemical systems into biological systems, their unity and interrelation confirms the synthesis of organic compounds from inorganic ones. In 1824, the German chemist F. Wöhler, a student of Berzelius, obtained for the first time from inorganic dicyanium MCCA, by heating it with water, oxalic acid HOOC-COOH, an organic compound. 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 in the 50-60s. 20th century was the first synthesis of simple proteins - the hormone insulin and the enzyme ribonuclease.
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Introduction
Under the influence of new production requirements, the doctrine of chemical processes arose, which takes into account the change in the properties of a substance under the influence of temperature, pressure, solvents and other factors. After that, chemistry becomes a science not only and not so much about substances as finished 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 began to be based on atmospheric nitrogen. The technology of petrochemical production has emerged with its flow systems providing continuous high-performance processes. chemical reaction electron
So, back in 1935, such materials as leather, furs, rubber, fibers, detergents, drying oil, varnishes, acetic acid, ethyl alcohol were produced entirely from animal and vegetable 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 oil and varnishes, 40% fibers, 70% rubber and about 25% leather materials were produced on the basis of gas and oil raw materials. In addition, chemistry provides annually hundreds of thousands of tons of urea and petroleum protein as feed for livestock and about 200 million tons of fertilizers.
Such impressive successes have been achieved on the basis of the doctrine of chemical processes - the field of science in which the most profound integration of physics, chemistry and biology has been carried out. This doctrine is based on chemical thermodynamics and kinetics, therefore this section of science equally belongs to physics and chemistry. One of the founders of this scientific direction was the Russian chemist N.N. Semenov - Nobel Prize winner, founder of chemical physics. In his 1965 Nobel lecture, he stated that the chemical process is the main 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, multilevel living systems. After all, any cell of a living organism, in essence, is a kind of complex reactor. Therefore, chemistry becomes a bridge from the objects of physics to the objects of biology.
The doctrine of chemical processes is based on the idea that the ability to interact with various chemical reagents is determined, among other things, by the conditions for the occurrence 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, in principle, feasible. 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.
Chemical Process Control Methods
In the most general form, methods for controlling chemical processes can be divided into thermodynamic and kinetic.
Thermodynamic methods affect the shift of the chemical equilibrium of the reaction. Kinetic methods affect the rate of a chemical reaction.
The separation of chemical thermodynamics into an independent direction is usually associated with the appearance in 1884 of the book by the Dutch chemist J. van't Hoff "Essays on Chemical Dynamics". It substantiates the laws that establish the dependence of the direction of a chemical reaction on temperature changes 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 absorb 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 heat 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 is shifted in one direction or another. It depends both on the nature of the reagents and on the process conditions. 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 precipitates.
However, there are many chemical reactions in which the equilibrium is shifted to the left, towards the formation of the starting substances. To implement them, 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 reactants (if the reaction occurs in the liquid phase).
Thermodynamic methods predominantly influence the direction of chemical processes rather than their speed.
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, the methods of mixing reagents, the 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, the most appropriate step-by-step solution, in which the strongest effect of any one of the "third bodies", most often a catalyst, is first highlighted.
In addition, it should be understood that almost all chemical reactions are by no means a simple interaction of the 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 ones. Impurities can have both catalytic and inhibitory effects. Therefore, to control the chemical process, certain additives are introduced into 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 an inhibition that inhibits the process.
As noted above, the ability of chemical elements to interconnect is determined not only by their molecular structure, but also by the conditions under which the connection occurs. These conditions affect the outcome of chemical reactions. In this case, substances with a variable composition, in which the bonds between individual components are weaker, experience the greatest impact. It is the reaction of such substances that is strongly influenced by various catalysts.
Catalysis - the acceleration of a chemical reaction in the presence of special substances - catalysts that interact with the reactants, 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 the interaction of liquid or gaseous reagents takes place on the surface of a solid catalyst;
* homogeneous catalysis - a chemical reaction takes place either in a gas mixture or in a liquid, where both the catalyst and the reagents are dissolved;
* electrocatalysis - the reaction takes place on the surface of the electrode in contact with the solution and under the action of an electric current;
* photocatalysis - the reaction takes place on the surface of a solid body or in a liquid solution and is stimulated by the energy of the absorbed radiation.
Heterogeneous catalysis is the most widespread, with its help 80% of all catalytic reactions in modern chemistry are carried out.
The use of catalysts served as the basis for a radical break in the entire chemical industry. Thanks to them, it became possible to use paraffins and cycloparaffins, which were still considered "chemical dead", as raw materials for organic synthesis. Catalysis is essential 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 more and more 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 wall material 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 when they were erroneous, turned out to be useful, if only because they prompted scientists to new experiments. The fact is that for most industrially important chemical processes, catalysts were selected through countless trial and error. So, for example, for the ammonia synthesis reaction in 1913-1914. German chemists tried more than 20 thousand chemical compounds as catalysts, following the periodic system of elements and combining them in various ways.
Today we can draw some conclusions about the essence of catalysis.
1. The reactants come into contact with the catalyst, interact with it, resulting in the weakening of chemical bonds. If the reaction occurs in the absence of a catalyst, then the molecules of the reactants must be activated by supplying energy to the reactor from outside.
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 overwhelming majority of cases, compounds of the berthollide type with a variable composition, which are characterized by the presence of weakened chemical bonds or even free valences, act as catalysts, which gives them high chemical activity. Molecules of compounds of the berthollide type contain a wide range of energetically inhomogeneous bonds or even free atoms on the surface.
4. The consequences of the interaction of the reagents with the catalyst are the course of the reaction in a given direction and an increase in the reaction rate, since the number of meetings of the reacting molecules on the catalyst surface increases. In addition, the catalyst captures some of the energy of the exothermic reaction for energy replenishment of all new reaction acts and its general acceleration.
At the present stage of its development, chemistry has discovered many effective catalysts. Among them are ion-exchange resins, organometallic compounds, membrane catalysts. Many chemical elements of the periodic system have catalytic properties, but the most important role is played by 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 allow not only 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).
The direction of development of the doctrine of chemical processes
In modern conditions, one of the most important directions in the development of the theory of chemical processes is the creation of methods for controlling these processes, therefore, chemical science is developing such problems as plasma chemistry, radiation chemistry, and the chemistry of high pressures and temperatures.
Plasma Chemistry
Plasma chemistry studies chemical processes in low-temperature plasma at temperatures from 1000 to 10,000°C. Such processes are characterized by an 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 rate of similar chemical processes in conventional reactors is reduced by 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, in one ten-thousandth of a second, about 80% of methane is converted into acetylene.
Plasma chemistry has recently been increasingly introduced into industrial production. Technologies have already been created for the production of raw materials for powder metallurgy, and synthesis methods have been developed for a number of chemical compounds. In the 1970s Plasma steel-smelting furnaces were created, which made it possible to obtain 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 fusion of rock particles and their strong compression with metal. In terms of its qualities, it surpasses ordinary concrete by tens and hundreds of times.
radiation chemistry
One of the youngest directions in the study of chemical processes is radiation chemistry, which originated in the second half of the 20th century. The subject of her developments was the transformation of a wide variety of substances under the influence of ionizing radiation. Sources of ionizing radiation are X-ray installations, particle accelerators, nuclear reactors, and radioactive isotopes. As a result of radiation-chemical reactions, substances receive 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 some polymer followed by irradiation. Such concretes have four times higher strength, water resistance and high corrosion resistance.
Chemistry of high pressures and temperatures
A fundamentally new and extremely important field of study of chemical processes is the self-propagating high-temperature synthesis of refractory and ceramic materials. Usually their production is carried out by the method of powder metallurgy, the essence of which is the pressing and compression at high temperature (1200--2000 ° C) of metal powders. Self-propagating synthesis 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, so 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 oxidants. Self-propagating high-temperature synthesis is based on this conclusion - the thermal process of combustion in solids. It is, 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 adaptable and easy to automate.
High pressure chemistry
Another area of development of the doctrine of chemical processes is the chemistry of high and ultrahigh pressures. Chemical transformations of substances at pressures above 100 atm are classified as high-pressure chemistry, and at pressures above 1000 atm, as superhigh-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 in recent years, installations have been used in which a pressure of 5000 atm is reached, and tests are carried out at a pressure of 600,000 atm, which is achieved due to the shock wave during the explosion within a millionth of a second. Nuclear explosions produce even higher pressures.
At high pressure, the electron shells of atoms approach and deform, 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 at high temperature and pressure becomes chemically active. With increasing pressure, many substances pass into the metallic state. So, in 1973, scientists observed metallic hydrogen at a pressure of 2.8 million atm.
One of the most important achievements of ultrahigh 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 have been 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 - carbonado, which are harder than natural diamonds. They are used to process the diamonds themselves.
At present, industrial production has been established not only of artificial diamonds, but also of other precious stones - corundum (red ruby), emerald, etc. At high pressures, other materials with high thermal stability are also synthesized. So, from boron nitride at a pressure of 100,000 atm and a temperature of 2000 ° C, borazone was synthesized - a material suitable for drilling and grinding parts from extremely hard materials at very high temperatures.
Energy of chemical processes and systems
Chemical reactions - the interaction 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 is capable of mass and heat exchange between all its constituent parts, then such a system is called thermodynamic. A chemical system in which reactions can take place is a special case of a thermodynamic system. If there is no mass and heat exchange between the system and the environment, then such a system is called isolated. If there is no mass transfer, but heat transfer is possible, then the system is called closed. If both mass and heat exchange is 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 the properties: temperature, pressure, concentration, volume, energy.
Reactions occurring in a homogeneous system develop in its entire volume and are called homogeneous. Reactions occurring at the interface are heterogeneous.
For the thermodynamic description of the system, the so-called state functions of the system are used - this is any physical quantity, the values of which 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);
The Gibbs energy is a measure of the stability of a system at constant pressure (G):
The 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 not possible. Thus, all processes can proceed spontaneously in the direction of decreasing free energy.
Chemical interaction, as a rule, is accompanied by a thermal effect. Processes that proceed 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 constituent parts.
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.
I law of thermodynamics (the law of conservation of energy) - energy does not disappear and does not arise again from nothing during the process, it can only pass from one form to another in strictly equivalent ratios.
II law of thermodynamics - when a process proceeds in an isolated system of reversible processes, the entropy remains unchanged, and in irreversible processes it increases. .
Conclusion
Chemistry is a social science. Its highest goal is to satisfy the needs of every individual and the whole society. Many hopes of mankind are turned to chemistry. Molecular biology, genetic engineering and biotechnology, materials science are fundamental chemical sciences. The progress of medicine and health protection is the problem of the chemistry of diseases, medicines, food; neurophysiology and the work of the brain is, first of all, neurochemistry, chemistry, the chemistry of memory. Mankind expects from chemistry new materials with magical properties, new energy sources and accumulators, new clean and safe technologies, and so on.
As a fundamental science, chemistry was formed at the beginning of the 20th century, along with a new, quantum mechanics. And this is an indisputable truth, because all objects of chemistry - atoms, molecules, ions, etc. are quantum objects. Major developments in chemistry are chemical reactions and chemical processes i.e. the rearrangement of atomic nuclei and the transformation of electron shells, the 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. Ways to solve the basic problem of chemistry based on the doctrine of the 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 of finished objects, but a science of the processes and mechanisms of change in matter. Thanks to this, she ensured the production of synthetic materials.
In modern society, the study of chemical processes is a necessary knowledge, since science needs to develop and strive for new discoveries, and only a person 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. Saxonov; ed. prof. A. I. Bochkareva. - Tolyatti: TGUS, 2008. - 386 p. [electronic resource] www.tolgas.ru (accessed 11/14/2102)
2. Sadokhin A.P. Concepts of modern natural science: a textbook for university students studying in the humanities and specialties of economics and management / A.P. Sadokhin. -- 2nd ed., revised. and additional - M.: UNITI-DANA, 2006. - 447 p.
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Study of the theory of self-organization. The main criterion for the development of self-organizing systems. Non-equilibrium 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 formation of the nucleus as one of the structural elements of the eukaryotic cell, which contains genetic information in DNA molecules. Nuclear shell, nucleus, matrix as structural elements of the nucleus. Characterization 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
The transformation of nitrogenous substances in plants. The quality of vegetable oils depending on environmental factors. The transformation of substances during the maturation of seeds of oil crops. Vernalization, its essence and significance. Effect of temperature and light on seed dormancy.
test, added 09/05/2011
Analysis of possible pathways for the breakdown of glucose. Determination of the components and principle of functioning of aerobic metabolism. The processes of formation of organic acids and biotransformation of initial substrates that are different 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. The second law of thermodynamics. Ideas about the structure of atoms. Methods of chemical kinetics. The 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 excretion 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 release of substances.
