Mutual transformations of compounds observed in wildlife, as well as occurring as a result of human activity, can be considered as chemical processes. Reagents in them can be either two or more substances that are in the same or in different states of aggregation. Depending on this, homogeneous or heterogeneous systems are distinguished. The conditions for conducting, 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 constituent parts of their molecules undergo changes, and the charges of the nuclei of atoms remain the same, they speak of chemical reactions or processes. The products formed as a result of their flow are used by man in industry, agriculture and everyday life. Huge number of interactionsbetween substances occurs, both in living and inanimate nature. Chemical processes have a fundamental difference from physical phenomena and properties of radioactivity. Molecules of new substances are formed in them, while physical processes do not change the composition of compounds, and atoms of new chemical elements arise in nuclear reactions.
Conditions for the implementation of processes in chemistry
They can be different and depend primarily 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 action 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) used in the food and microbiological industries are widespread. 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 chlorine derivatives of methane (dichloromethane, trichloromethane, carbon tetrachloride, resulting from chain reactions.
Homogeneous catalysis
They are 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 acceleratorsreactions, consist in carrying out reactions in the entire volume of mixtures. If the catalyst is in the same state of aggregation as the reactants, it forms mobile intermediate complexes with the starting compounds.
Homogeneous catalysis is a basic chemical process used in, for example, oil refining, 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. So-called active centers are formed on it. These are areas where the interaction of the reacting compounds proceeds very quickly, that is, the reaction rate is high. They are species-specific and play an important role also 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 the contact apparatus, a gaseous mixture of sulfur dioxide and oxygen is heated and passed through lattice shelves filled with dispersed powder of vanadium oxide or vanadyl sulfate VOSO4. The resulting product, sulfur trioxide, is then absorbed by concentrated sulfuric acid. A liquid called oleum is formed. It can be diluted with water to obtain the desired concentration of sulfate acid.
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 fuel: natural gas, coal, peat. They are 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, in the process of digestion, proteins, lipids and carbohydrates are broken down under the action of biologically active substances - enzymes.
The released energy is accumulated in the form of macroergic bonds 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 it are called endothermic. In the organic synthesis industry and other technologies, the thermal effects of thermochemical reactions are calculated. It is important to know this, for example, for the correct calculation of the amount of energy used to heat the reactors and synthesis columns in which reactions take place, accompanied by heat absorption.
Kinetics and its role in the theory of chemical processes
Calculating the speed of reacting particles (molecules, ions) is the most important task facing the industry. Its solution ensures the economic effect and profitability of technological cycles in chemical production. For increasethe rate of such a reaction, such as the synthesis of ammonia, the decisive factors will be a change in pressure in a gas mixture of nitrogen and hydrogen up to 30 MPa, as well as the prevention of a sharp increase in temperature (the temperature is 450-550 °C is optimal).
Chemical processes used in the production of sulfate acid, namely: pyrites burning, sulfur dioxide oxidation, absorption of sulfur trioxide by oleum, are carried out under various conditions. For this, a pyrite furnace and contact devices are used. They take into account the concentration of reactants, temperature and pressure. All these factors are correlated to carry out the reaction at the highest rate, which increases the yield of sulfate acid to 96-98%.
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 interaction (reactions of combination, substitution, decomposition, exchange). Molecules and atoms of chemical elements are in constant motion. As scientists have established, all of the above types of chemical reactions 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 these are the cycles of substances such as oxygen, carbon dioxide and nitrogen. In the next heading, we look at how nitrogen circulates in the atmosphere, soil, andliving organisms.
Interconversion of nitrogen and its compounds
It is well known that nitrogen is a necessary component of proteins, which means that it is involved in the formation of all types of earthly 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 form 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, referring, among other things, to their ability to synthesize proteins.
Herbivores get their peptides from plant foods, while carnivores get their peptides from prey meat. 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 absorbed by plants. Nitrogen enters through the stomata of the skin of the leaves, and solutions of nitric and nitrous acids and their s alts are absorbed by the root hairs of the roots of plants. The cycle of nitrogen transformation closes to repeat again. The essence of chemical processes occurring with nitrogen compounds in nature was studied in detail at the beginning of the 20th century by 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, pipelines are used. The surface of the equipment is in contact with aggressive media under high pressure. Moreover, almost all chemical production processes are carried out at high temperatures. Relevant is the production of materials with high rates of thermal and acid resistance, anti-corrosion properties.
Powder metallurgy includes the production of metal-containing powders, sintering and incorporation into 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, metals and their alloys, ceramics, and plastics are used. Calcium silicate, white clay, strontium and barium ferrides are used as fillers. All of the above substances give composite materials impact resistance, heat and wear resistance.
What is chemical engineering
The branch of science that studies 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 made up of mathematics, cybernetics, physical chemistry, and industrial economics. It does not matter what chemical process is involved in the technology (obtaining nitrate acid, decomposition of limestone, synthesis of phenol-formaldehyde plastics) - in modern conditions it is impossible without automated control systems that facilitate human activities, eliminate environmental pollution, and ensure continuous and waste-free chemical production technology.
In this paper, we considered examples of chemical processes occurring both in wildlife (photosynthesis, dissimilation, nitrogen cycle) and in industry.
