What is the chemical process? The chemical process: the essence and role in nature

Mutual transformations of compounds observed in living nature, as well as those resulting from human activities can be regarded as chemical processes. Reagents in them can be either two or more substances that are in one or in different aggregate states. Depending on this, homogeneous or heterogeneous systems are distinguished. The conditions of carrying out, the features of the course and the role of chemical processes in nature will be considered in this paper.

What is meant by a chemical reaction

If, as a result of the interaction of the initial substances, the components of their molecules undergo changes, and the charges of the atomic nuclei remain the same, one speaks of chemical reactions or processes. Products that are formed as a result of their flow, are used by man in industry, agriculture and everyday life. A huge number of interactions between substances occur, both in living and in inanimate nature. Chemical processes have a fundamental difference from the physical phenomena and properties of radioactivity. They form molecules of new substances, while physical processes do not change the composition of compounds, and in nuclear reactions, atoms of new chemical elements are formed.

Conditions for the implementation of processes in chemistry

They can be different and depend, first of all, on the nature of the reagents, the need for external energy supply, and also the aggregate state (solids, solutions, gases) in which the process takes place. 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 (obtaining ammonia), light energy (photosynthesis). With the participation of enzymes in living nature, the processes of the chemical reaction of fermentation (alcohol, lactic acid, butyric acid) used in the food and microbiological industries are widespread. To obtain products in the industry of organic synthesis, one of the main conditions is the presence of a free-radical mechanism of the chemical process. An example can be the production of chlorine derivatives of methane (dichloromethane, trichloromethane, carbon tetrachloride, formed as a consequence of chain reactions.

Homogeneous catalysis

They are special types of contact of two or more substances. The essence of the chemical processes occurring in a homogeneous phase (for example, gas-gas) with the participation of reaction accelerators consists in carrying out reactions in the entire volume of the mixtures. If the catalyst is in the same aggregate state as the reagents, it forms mobile intermediate complexes with the starting compounds.

Homogeneous catalysis is the main chemical process, for example, in the processing of petroleum, the production of gasoline, naphtha, gas oil, and other fuels. It uses technologies such as reforming, isomerization, catalytic cracking.

Heterogeneous catalysis

In the case of heterogeneous catalysis, the contact of the reactants occurs, most often, on the solid surface of the catalyst itself. It forms the so-called active centers. These are areas in which the interaction of reacting compounds takes place very quickly, that is, the reaction rate is high. They are species-specific and play an important role also if the chemical processes take place in living cells. Then they talk about metabolism - metabolic reactions. An example of heterogeneous catalysis is the industrial production of sulfate acid. In the contactor, a gaseous mixture of sulfur dioxide and oxygen is heated and passed through a lattice shelf filled with a dispersed vanadium oxide powder or vanadyl sulfate VOSO ₄ . The resulting product is sulfur trioxide, then it is absorbed by concentrated sulfuric acid. A liquid is formed, called oleum. It can be diluted with water to obtain the desired concentration of sulfate acid.

Features of thermochemical reactions

The isolation or absorption of energy in the form of heat is of great practical importance. Suffice it to recall the reaction of burning fuel: natural gas, coal, peat. They are physicochemical processes, the important characteristic of which is the heat of combustion. Thermal reactions are widespread both in the organic world and in inanimate nature. For example, in the process of digestion, proteins, lipids and carbohydrates are cleaved under the action of biologically active substances - enzymes.

The released energy is accumulated in the form of macroergic bonds of ATP molecules. The reactions of dissimilation are accompanied by the release of energy, part of which is dissipated as heat. As a result of digestion, each gram of protein gives 17, 2 kJ of energy, starch - 17, 2 kJ, fat - 38.9 kJ. The chemical processes that proceed with the release of energy are called exothermic, and with the absorption of it - endothermic. In the industry of organic synthesis and other technologies, the thermal effects of thermochemical reactions are calculated. This is important to know, for example, for the correct calculation of the amount of energy that is used to heat reactors and synthesis columns in which reactions occur accompanied by heat absorption.

Kinetics and its role in the theory of chemical processes

The calculation of the velocity of reacting particles (molecules, ions) is the most important task facing the industry. Its solution provides economic benefits and profitability of technological cycles in chemical production. To increase the speed of such a reaction, for example, the synthesis of ammonia, the decisive factors will be the change in pressure in the gas mixture of nitrogen and hydrogen up to 30 MPa, and also to prevent a sharp increase in temperature (the optimum temperature is 450-550 ° C).

Chemical processes used in the production of sulphate acid, namely: burning of pyrites, oxidation of sulfur dioxide, the absorption of sulfur trioxide by oleum is carried out under various conditions. For this, a pyrite furnace and contact apparatuses are used. They take into account the concentrations of reactants, temperature and pressure. All these factors correlate to carry out the reaction at the highest rate, which increases the yield of sulphate acid to 96-98%.

The cycle of substances, as physicochemical processes in nature

The well-known saying "Movement is life" can also be applied to chemical elements entering into various types of interaction (reactions of compound, substitution, decomposition, exchange). Molecules and atoms of chemical elements arrive in continuous motion. As established by scientists, all of the above types of chemical reactions can be accompanied by physical phenomena: the release of heat or its absorption, emission of photons of light, a change in the aggregate state. These processes occur in every shell of the Earth: the lithosphere, the hydrosphere, the atmosphere, the biosphere. The most significant of these are the cycles of substances such as oxygen, carbon dioxide and nitrogen. In the next heading, we will look at how nitrogen is circulated in the atmosphere, soil and living organisms.

Interconversion of nitrogen and its compounds

It is well known that nitrogen is a necessary constituent of proteins, and therefore participates in the formation of all types of terrestrial life, without exception. Nitrogen is assimilated by plants and animals in the form of ions: ammonium, nitrate and nitrite ions. Plants as a result of photosynthesis form not only glucose, but also amino acids, glycerin, fatty acids. All of the above listed 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, having in view, among other things, their ability to synthesize proteins.

Herbivores receive peptides from plant foods, and carnivores - from the meat of the victims. 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 passes into an inorganic form (ammonia, free nitrogen, nitrates and nitrites are formed). Returning to the atmosphere and soil, all these substances are again assimilated by plants. Nitrogen enters through the stomata of the skin of the leaves, and solutions of nitric and nitrous acids and their salts are absorbed by the root hairs of the plant roots. The nitrogen conversion cycle closes to be repeated. The essence of the chemical processes occurring with nitrogen compounds in nature was studied in detail in the early 20th century by the Russian scientist DN Pryanishnikov.

Powder Metallurgy

Modern chemical processes and technologies make a tangible 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, plastics. In their production heat exchangers, contact devices, synthesis columns, pipelines are used. The surface of the equipment is in contact with aggressive media under high pressure. Moreover, almost all processes of chemical production are carried out under the influence of high temperatures. Relevant is the production of materials with high levels of thermal and acid resistance, anti-corrosion properties.

Powder metallurgy includes the processes of production of metal-containing powders, sintering and introduction 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 the reactions of obtaining composite materials. These include foams, cermets, norpapalsts. As a matrix for production use metals and their alloys, ceramics, plastics. As fillers, calcium silicate, white clay, strontium ferrium and barium are used. All of the above substances impart composite materials to impact resistance, heat and wear resistance.

What is chemical technology?

The branch, science, engaged in the study of the 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 is mathematics, cybernetics, physical chemistry, industrial economics. It does not matter which chemical process is involved in the technology (nitrate production, limestone decomposition, phenol-formaldehyde plastics synthesis) - in modern conditions it is impossible without automated control systems that facilitate human activity excluding environmental pollution and provide a continuous and non-waste technology of chemical production.

In this paper we have considered examples of chemical processes that occur, both in living nature (photosynthesis, dissimilation, nitrogen cycling), and in industry.