Solid starting materials can react with each other and when separated spatially. In this regard, unlike conventional solid-phase reactions, it is not necessary to use starting materials in stoichiometric quantities. The final product, regardless of the ratio of the starting substances, will have a stoichiometric composition.
Solid starting materials and reaction products do not affect the displacement of heterogeneous chemical equilibrium.
Solid starting materials can react with each other and when separated spatially. In this regard, in ex. The final product, regardless of the ratio of the starting substances, will have a stoichiometric composition.
Reactions between solid starting materials can be accelerated due to the fact that the solids bind to each other through a transport reaction. It can be foreseen that this principle will be carried over to numerous reactions between solids. At the same time, it is especially favorable that it is possible to select the appropriate transport reactions based on simple theoretical concepts.
The granulometric composition of the loaded particles of the solid starting material and the hydrodynamic regime of the process do not change.
Only those molecules of the solid starting substance AI that enter the adsorption centers filled with the substance AZ participate in the chemical reaction.
Thus, the composition of the melt with a continuous supply of solid starting materials is determined by the ratio PiSy / p2sH, and with different sizes of pieces of lime and carbon we will obtain different melt compositions.
To obtain an aqueous extract, 50 - 80 mg of the solid starting material is boiled for several minutes with 3 ml of water, which is replenished dropwise as the solution evaporates. An aqueous extract that has a neutral reaction (neutral aqueous extract) may contain interfering cations that must be removed with soda in the same way as is done if the object under study is a liquid (see page. As a result of neutralization of an alkaline (after action with soda) liquid and separating the precipitate, the prepared solution is obtained.
Rate-time curves for silver oxalate degradation. G110 S. dots indicate the results of experiments without breaks, circles indicate experiments with breaks of 60 minutes. (/ and 30 minutes (/ /. Such experiments show at the same time that simple mixing of a solid starting material with a solid product may not be enough to detect the autocatalytic effect of the latter.
Chemical technological process, in which gaseous starting substances are blown through holes at the bottom of the apparatus, and the solid starting substances in it seem to boil, being in a suspended state all the time. In this case, the reactions take place in the fluidized bed itself.
Chemist is a technological process in which gaseous starting substances are blown through holes at the bottom of the apparatus, and the solid starting substances in it seem to boil, being constantly in suspension. In this case, reactions take place in the fluidized bed itself.
Typical curves a f (t of the process of thermal dissociation of solids. Explanations are given in the text. When describing the course of thermal dissociation, the reaction rate is most often made dependent on the composition of the solid phase, expressed by the degree of transformation (decomposition) a of the solid starting substance. In Fig. VIII- Figure 12 shows the most typical dependences of a on reaction time.
In table 22 summarizes data concerning the possibility of finding anions in the analytical fractions described above, resulting from the preparation of a solution from the solid starting material to be analyzed.
In the dehydration of manganese oxalate dihydrate, studied from the point of view of Volmer's theory, for which the formation of an amorphous product and its subsequent crystallization was x-ray proven, the growth of nuclei of a solid, amorphous product was observed before the formation of a crystalline product, which proves the special catalytic properties of the interface: solid initial substance/solid and for the radiographically amorphous state. Crystallization of an amorphous product may, however, be important for explaining the dependence of rate on vapor pressure during the decomposition of crystalline hydrates. In these cases, the formation of a layer of an amorphous product that is difficult to penetrate for water molecules can lead to a decrease in the reaction rate.
Ft - flow of solid matter entering the apparatus, kg/hour; Fg (0) - flow of gaseous substance entering the apparatus, kg/hour; Fg - flow of gaseous substance entering into chemical interaction, kg/hour; Fr is the volume occupied by the gas phase in the reaction volume of the apparatus, m3; GT is the weight of the solid starting material in the reaction volume of the apparatus, kg; GT is the weight of the gaseous starting substance in the reaction volume of the apparatus, kg; скв - equivalent concentration of the gaseous starting substance in the reaction volume of the apparatus, kg/m8; a is the stoichiometric coefficient of transition from the substance flow Ft to the flow Fg; &g, / sg - solid and gaseous phase unloading coefficients, l / hour; K is the reaction rate constant; F (n) - function reflecting the order of the reaction; X - output coordinate (temperature); Ta is the time constant of the thermal model of the reaction volume of the apparatus; K7 is the gain coefficient of the thermal model of the reaction volume of the apparatus.
A mixture of 5 1 g of cyclopentadienyl manganese tricarbonyl, 13 7 g of phosphorus trichloride, 4 25 g of aluminum chloride and 15 ml of isopentane was heated with vigorous stirring and kept at a temperature of 45 - 50 C for 3 hours. Before heating, the mixture is a suspension of solid starting materials in solution yellow color.
It is important to determine which ions are missing in the sample. Preliminary tests) are mainly carried out with solid starting materials, the solutions are evaporated.
Very often, the rate of dissolution of the starting material is so insignificant or the reaction product is so slightly soluble that the new phase is densely deposited on the original one and, due to this, its external shape repeats the shape of the original substance. Such transformations, which occur at the interface of a solid starting material and lead to the production of solid final products, are called topochemical reactions in the narrow sense of the word. In contrast to reactions occurring in the bulk of a solution, the degree of dispersion of the reaction products in this case is similar to the dispersion of the starting substances. The topochemical method of consideration is therefore special, but applicable in the description of catalysts, electrolytic separation of metals and in matters of corrosion.
If vapor pressure promotes reactions between solids, then we should expect the same for chemical transport reactions. What opportunities do transport reactions provide as a means of interaction between solid starting substances?
In solid-phase reactions, the transformation can begin only in the bulk of the phase, and then develop at the interface between the new and old phases. Such reactions, where the transformation zone or front passes along the interface between the solid starting material and the solid product, are called topochemical. An example of such reactions is the weathering of crystalline hydrates. Faraday also noticed that well-cut transparent crystals of Cu2SO4 - 5H2O do not lose water in dry air for a long time. If a scratch is applied to their surface or a break is made, then rapid dehydration of the crystal immediately begins, which always spreads from the damaged area.
The fact that many anions can be detected fractionally does not mean that the discovery of anions is an easier task than the discovery of cations. Even with the limited number of anions that are studied in this textbook, the analysis is very difficult if the starting material is a solid that is insoluble in water. Such a substance must be treated with soda (soda extract), which is associated with a number of complications in the work.
When writing reactions between solutions of electrolytes, each time you need to imagine whether there is any reason interfering with the actual occurrence of this or that reaction. For example, if an electrolyte solution interacts with solid substances and one of the products is slightly soluble, then the reaction can quickly stop due to the fact that a layer of also a solid reaction product is formed on the surface of the solid starting substance, preventing its further progress. That is why, to produce carbon dioxide by the action of acid on marble, they take hydrochloric acid, and not sulfuric acid, since in the case of sulfuric acid the marble is quickly covered with a layer of gypsum (CaSO4 - 2H2O) and the reaction practically does not occur.
To react bismuth with fluorine, a fluidized bed reactor is used. The fluidized bed synthesis technique, borrowed from technology, has the following advantages: rapid establishment of thermal equilibrium in the reaction mixture, absence of sintering of solid reaction products, good heat exchange with the walls of the tube, large surface solid starting materials and therefore rapid conversion.
For the g - t system, an increase in the contact surface of the phases is achieved by grinding the solid phase. The gaseous substance is brought into contact with the crushed starting substance by the most in a variety of ways For example, solid particles of a substance are placed on reactor shelves, and a gas flow moves above the shelves. In other cases, a finely divided solid starting material is sprayed into a stream of gaseous starting material in a hollow volume; This is how pulverized fuel is burned in the furnaces of steam boilers.
In fast industrial processes, reactions in mixtures of solids usually proceed at rates thousands of times greater than would be possible with direct interaction of solid phases. The thickness of the layer of the resulting product is almost the same over the entire surface of the grain it covers. This is explained by the fact that reactions occurring between solid starting substances actually occur with the participation of gaseous or liquid phases.
In the development of the chemistry of solid-phase reactions, discussions often arose on the question of whether solid substances could react with each other without the participation of a liquid or gas. This issue has now been resolved in favor of the existence of purely solid-phase reactions. It is interesting, however, that it can be shown in a number of transformations with solid starting materials that some liquid or gaseous phase nevertheless participates as a reaction mediator. However, generalizations in this area should be avoided; on the contrary, it is necessary to experimentally study the state of the system in each individual case. Budnikov and Ginstling carried out such research in particular detail.
If the problem of the initial substance for oil and gas formation as a whole can be considered solved, then the problem of the mechanism of oil and gas formation, which is key, still requires a solution in detail. The common composition of organic matter, sedimentary rocks and hydrocarbons (HC) is an important argument in favor of a biosphere source of oil and gas. The role of thermal energy (heating) for the production of liquid and gas hydrocarbons from a solid starting material is also obvious. These circumstances made it possible to create a concept about hydrocarbon generation centers and formulate ideas about the main phases of gas and oil formation, which have become widespread throughout the world.
The rate of reactions occurring without the participation of gaseous and liquid phases is so small that they cannot have a large practical significance in fast industrial processes. But in practice, reactions in mixtures of solids usually proceed at rates thousands of times greater than would be possible with direct interaction of solids. The thickness of the layer of the resulting product is almost the same over the entire surface of the grain it covers. This is explained by the fact that reactions occurring between solid starting substances actually occur with the participation of gaseous or liquid phases.
The rate of such reactions, occurring without the participation of gaseous and liquid phases, is so low that they cannot be of great practical importance in fast industrial processes, carried out, in particular, in the production of salts. In practice, reactions in mixtures of solids usually occur at rates thousands of times greater than would be possible with direct interaction of solids. The thickness of the layer of the resulting product is almost the same over the entire surface of the grain it covers. This is explained by the fact that reactions occurring between solid starting substances actually occur with the participation of gaseous or liquid phases.
The rate of reactions occurring without the participation of gaseous and liquid phases is so low that they cannot be of great practical importance in fast industrial processes. But in practice, reactions in mixtures of solids usually proceed at rates thousands of times greater, or than would be possible with direct interaction of solids. The thickness of the layer of the resulting product is almost the same over the entire surface of the grain it covers. This is explained by the fact that reactions occurring between solid starting substances actually occur with the participation of gaseous or liquid phases.
It is incredible that these compressive stresses, in relation to which solids are stronger than in relation to tension, have reached the value necessary to destroy microscopic crystals. Direct experiments to study the dependence of the rate of decomposition of potassium permanganate on the size of the surface, which is inversely propo. This shows that fragmentation itself is not always the cause of the observed acceleration of the reaction. Explaining the acceleration of the reaction of solids by the existence of branched chain reactions also encounters some difficulties. Conditions in the solid phase differ significantly from those in the gas or liquid phase due to their heterogeneity. If a chain mechanism exists, then such a reaction is still limited to the interface between the solid starting material and the reaction product. Consequently, even in the presence of a chain mechanism, the question arises about the reasons for the special properties of the interface: initial solid substance / solid product.
IN modern science distinguish between chemical and nuclear reactions that occur as a result of the interaction of starting substances, which are usually called reagents. As a result, other chemical substances, which are called products. All interactions occur under certain conditions (temperature, radiation, presence of catalysts, etc.). Nuclei of reactant atoms chemical reactions don't change. In nuclear transformations, new nuclei and particles are formed. There are several different signs by which the types of chemical reactions are determined.
The classification can be based on the number of starting and resulting substances. In this case, all types of chemical reactions are divided into five groups:
- Decompositions (several new ones are obtained from one substance), for example, decomposition when heated into potassium chloride and oxygen: KCLO3 → 2KCL + 3O2.
- Compounds (two or more compounds form one new one), interacting with water, calcium oxide turns into calcium hydroxide: H2O + CaO → Ca(OH)2;
- Substitution (the number of products is equal to the number of starting substances in which one component is replaced by another), iron in copper sulfate, replacing copper, forms ferrous sulfate: Fe + CuSO4 → FeSO4 + Cu.
- Double exchange (molecules of two substances exchange the parts that leave them), metals in and exchange anions, forming precipitated silver iodide and cadium nitrate: KI + AgNO3 → AgI↓ + KNO3.
- Polymorphic transformation (a substance transitions from one crystalline form to another), when heated, color iodide turns into yellow mercury iodide: HgI2 (red) ↔ HgI2 (yellow).
If chemical transformations are considered based on changes in the oxidation state of elements in the reacting substances, then the types of chemical reactions can be divided into groups:
- With a change in the degree of oxidation - redox reactions (ORR). As an example, we can consider the interaction of iron with hydrochloric acid: Fe + HCL → FeCl2 + H2, as a result, the oxidation state of iron (a reducing agent that donates electrons) changed from 0 to -2, and of hydrogen (an oxidizing agent that accepts electrons) from +1 to 0.
- Without changing the oxidation state (i.e., not ORR). For example, the acid-base reaction of hydrogen bromide with sodium hydroxide: HBr + NaOH → NaBr + H2O, as a result of such reactions salt and water are formed, and the oxidation states chemical elements included in the starting substances do not change.
If we consider the rate of flow in the forward and reverse directions, then all types of chemical reactions can also be divided into two groups:
- Reversible - those that simultaneously flow in two directions. Most reactions are reversible. An example is the dissolution of carbon dioxide in water to form unstable carbonic acid, which decomposes into the starting substances: H2O + CO2 ↔ H2CO3.
- Irreversible - flow only in the forward direction, after complete consumption of one of the starting substances they are completed, after which only products and the starting substance taken in excess are present. Typically one of the products is either a precipitated insoluble substance or a liberated gas. For example, during the interaction of sulfuric acid and barium chloride: H2SO4 + BaCl2 + → BaSO4↓ + 2HCl, an insoluble precipitate
The types of chemical reactions in organic chemistry can be divided into four groups:
- Substitution (one atoms or groups of atoms are replaced by others), for example, when chloroethane reacts with sodium hydroxide, ethanol and sodium chloride are formed: C2H5Cl + NaOH → C2H5OH + NaCl, that is, the chlorine atom is replaced by a hydrogen atom.
- Addition (two molecules react and form one), for example, bromine adds at the site of the break of the double bond in the ethylene molecule: Br2 + CH2=CH2 → BrCH2—CH2Br.
- Elimination (a molecule decomposes into two or more molecules), for example, under certain conditions, ethanol decomposes into ethylene and water: C2H5OH → CH2=CH2 + H2O.
- Rearrangement (isomerization, when one molecule turns into another, but the qualitative and quantitative composition of the atoms in it does not change), for example, 3-chloro-ruthene-1 (C4H7CL) turns into 1 chlorobutene-2 (C4H7CL). Here the chlorine atom went from the third carbon atom in the hydrocarbon chain to the first, and the double bond connected the first and second carbon atoms, and then began to connect the second and third atoms.
Other types of chemical reactions are also known:
- They occur with absorption (endothermic) or release of heat (exothermic).
- By type of interacting reagents or products formed. Interaction with water - hydrolysis, with hydrogen - hydrogenation, with oxygen - oxidation or combustion. The elimination of water is dehydration, of hydrogen is dehydrogenation, and so on.
- According to the conditions of interaction: in the presence of catalysts (catalytic), under the influence of low or high temperature, with changes in pressure, in light, etc.
- According to the reaction mechanism: ionic, radical or chain reactions.
From crude oil extracted from the depths of the earth, various petroleum and waxy products are obtained by distillation. In cosmetics, primarily liquid flowing paraffin (or white) oil, viscous dense petroleum jelly, hard, waxy mountain wax (or ozokerite) and purer paraffin are used.
Paraffin oil is a transparent, odorless, tasteless oily substance that can be of varying densities.
Vaseline is a white, viscous, sticky, oily substance that is odorless. In this form, it is used as an ointment for massage, and also as a base for the preparation of various medicinal ointments.
Ozokerite and paraffin are solid white substances of variable density.
All these petroleum-derived raw materials are widely used in the cosmetics industry due to their low price and good storage stability. They cannot be easily absorbed into the skin, but are an excellent source material for the production, for example, of gel and cosmetic milk, as well as for decorative cosmetics.
Natural oils, due to the presence of unsaturated bonds in them, are less viscous and more fluid than fats. Both oils and fats are esters of fatty acids and glycerol; in nature they are always found in the form of various mixtures. Natural fats quickly deteriorate due to their chemical unsaturation. Therefore, they are often hydrogenated by adding hydrogen atoms at unsaturated bonds. In this form, the fat becomes hard and is better preserved, but at the same time it becomes less suitable for use in cosmetics Villamo H. Cosmetic chemistry. - M.: Mir, 1990..
Fats of plant and animal origin are still used for the production of cosmetic substances, although for the above reasons they are increasingly giving way to synthetic substances, fatty acids, fatty alcohols, etc. The most important plant and animal oils and fats are the following (Table 1) Chemistry in everyday life and in production. / Ed. Selivanova M.I. - M.: Chemistry, 2000..
Table 1 Vegetable and animal oils and fats
In addition to the above, some other natural oils are also used, since they contain certain additional substances. The following are examples.
Turtle oil in its raw form is yellow in color and has a very bad smell(it is obtained by extraction from the genitals and muscles of one of the turtle species). It contains, in particular, vitamins A, O, K and H, as well as linoleic and linolenic acids. After purification, it becomes a usable cosmetic raw material.
Mink oil, like the previous one, is an animal oil rich in vitamins (it is obtained from mink muscles).
In addition to oils, oil from sprouted wheat seeds always contains 2-12% fatty acids. It is well preserved and rich, in particular, in vitamin E, carotene, linoleic and linolenic acids, ergosterol, and also contains large quantities vitamin K.
The most important natural wax used in the manufacture of gels is beeswax. It is a hard yellow or (when bleached) white viscous substance. Beeswax contains 72% of various natural waxes (wax esters), about 14% of free high-molecular fatty acids, free fatty alcohols, etc.
Carnauba wax is obtained from the leaves of the carnauba palm tree. This is the hardest of natural waxes. It mixes well with many fats, oils, waxes, etc., increasing their melting point and increasing the hardness of the composition.
Wool fat is a fat-like substance obtained from sheep's wool as a result of washing it. When 25% water is added to wool fat, a substance called lanolin is obtained. Raw lanolin is yellow-brown in color, but when purified it is almost white. It contains a large amount of cholesterol (largely esterified with various fatty acids), various waxes, as well as free high-molecular fatty acids and fatty alcohols.
Thus, purified lanolin is quite suitable as a starting material. In addition, various products are made from it for various purposes, such as lanolin oil and various fractions of lanolin.
All natural fats and oils are triglycerides, i.e. esters of the tribasic alcohol glycerol. There are no fats or oils in nature in which glycerol is esterified with only one fatty acid; Natural fats are always esters of two or more fatty acids.
Animal fats (such as lard) and vegetable fats can be hydrolyzed with water at high temperature and pressure into fatty acids and glycerol. As a result, mainly stearic acid, palmitic acid and myristic acid are obtained. All three acids are solid, waxy substances, colorless and odorless. In this form, they are excellent raw materials for the preparation of creams, gels and various emulsions.
Natural oils, in addition to the above acids, also contain unsaturated fatty acids, such as oleic acid with one double bond, linoleic acid with two double bonds and linolenic acid with three double bonds. Unsaturated fatty acids and their esters are liquid at room temperature. Due to the presence of double bonds in them, they are very sensitive to decomposition reactions, for example, to the action of microbes, and easily break down into smaller molecules, which often have an unpleasant odor. Thus, they spoil quickly. Therefore, they are usually hydrogenated at double bonds, and from all three of the above unsaturated fatty acids, stearic acid is formed; at the same time they all become hard, which is why this method is called fat hardening.
Wax is formed from an ester of a low molecular weight carboxylic acid, such as acetic acid, and a macromolecular so-called fatty alcohol; fatty alcohols are obtained, in particular, by the decomposition of natural waxes. For the preparation of gels, the most important raw materials are stearic alcohol and cetyl alcohol.
These relatively high molecular weight compounds, obtained by processing natural fats and waxes, are widely used in cosmetics. They are waxy or fat-like substances that adhere well to the skin. They easily mix with sebum and create an excellent addition to the base of creams, gels and other products, improving their properties.
As noted earlier, natural fats, oils and waxes are always mixtures containing a large number of different organic compounds. Therefore, depending on the place of origin and other environmental factors, they differ in their composition and properties. Modern industry, however, strives to produce cosmetic products of constant quality, so sustainable synthetic substances have noticeably replaced natural products.
By processing natural fats and waxes, as described above, fatty acids, fatty alcohols and, of course, glycerin necessary for industrial production are obtained. By combining them again synthetically, pure and stable fats and waxes are obtained. According to their origin and manufacturing method, they are called semi-synthetic products.
Synthetic waxes include esters of stearic, palmitic and myristic acids, obtained in large quantities from natural substances. The second component in them is most often isopropyl alcohol.
Silicones represent a very important group of synthetic fatty and waxy raw materials. These substances are based on a chain of alternating silicon and oxygen atoms, to which side organic groups are attached. An example of silicones is silicone oil, which is a relatively low molecular weight derivative of methylsiloxane.
Speaking about the properties of silicones, it should be noted that they are shelf stable and, in addition, are well tolerated by the body. They do not soften with increasing temperature (this is very important for using them as a liquid component of dense cosmetics), mix well with sebum and form a water-repellent film when used generously.
A polyalcohol (polyol) is an organic compound whose molecule contains more than one hydroxyl group OH. Ethylene glycol and glycerol, having two and three OH groups, respectively, are the simplest polyalcohols. This group also includes all sugars and various glycol derivatives, such as polyethylene glycols, which have already been discussed above. In gels, polyalcohols are used as humectants; in this sense, the most important are glycerin, propylene glycol, sorbitol and fructose.
Colloids include a variety of substances of plant and animal origin that form colloidal solutions with water; many of them are polysaccharides. Of the colloids having a polysaccharide base, the following can be mentioned (Table 2).
Table 2 Colloids having a polysaccharide base
Adhesives are usually products of plant origin. Only a small part of plant adhesives is listed here. Agar-agar, which belongs to the group of alginates, is well known; it is obtained from seaweed and is used to produce gummy-type sweets.
Dextran is produced using certain microorganisms from cane sugar. It is a polymer whose molecular weight ranges between 75,000 and 1,000,000. In addition to being used as a blood plasma substitute, it can be used, for example, to regulate the viscosity of solutions.
Celluloses are a widely used and quite diverse group of substances, of which only three examples are given above. Among the various forms of application for cosmetic purposes, their functions as a viscosity regulator for solutions and as a stabilizer for emulsions are important.
Colloids that have a protein base are, in particular, gelatin, obtained from bones and skins, soy and corn proteins, casein - the protein substance of milk, and albumin, which is obtained from egg whites.
It is characteristic of colloids that they are suitable for forming gels and increasing the viscosity of solutions and emulsions.
Modern emulsion technology uses various types of cellulose, mainly as stabilizers. They are also used as the main component of face masks, as well as in various hair care products.
In addition, protein colloids are used in skin care preparations because they are constructed from amino acid chains of varying lengths and, depending on the processing method, may also contain free amino acids; thus, they can be compared with protein hydrolysates Chemistry for cosmetic products. / Ed. Ovanesyan P.Yu. - Krasnoyarsk: March, 2001. .
The work was added to the site website: 2015-07-05">24. "> ">Signs of reversible and irreversible reactions. Equilibrium criteria. Equilibrium constant. Le Chatelier's principle.
;color:#000000;background:#ffffff">1. The reaction is called;color:#000000;background:#ffffff">reversible;color:#000000;background:#ffffff">, if its direction depends on the concentrations of the substances participating in the reaction. For example N;vertical-align:sub;color:#000000;background:#ffffff">2;color:#000000;background:#ffffff"> + 3H;vertical-align:sub;color:#000000;background:#ffffff">2;color:#000000;background:#ffffff"> = 2NH;vertical-align:sub;color:#000000;background:#ffffff">3;color:#000000;background:#ffffff"> at a low concentration of ammonia in the gas mixture and high concentrations of nitrogen and hydrogen, ammonia is formed; on the contrary, at a high concentration of ammonia it decomposes, the reaction proceeds in the opposite direction. Upon completion reversible reaction, i.e., when chemical equilibrium is achieved, the system contains both starting substances and reaction products.
;color:#000000;background:#ffffff">Irreversible reactions;color:#000000;background:#ffffff"> reactions in which the taken substances are completely converted into reaction products that do not react with each other under given conditions, for example;background:#ffffff">, ;color:#000000;background:#ffffff">burning;background:#ffffff"> ;color:#000000;background:#ffffff">hydrocarbons;background:#ffffff">, ;color:#000000;background:#ffffff">education;color:#000000;background:#ffffff">low dissociating;background:#ffffff"> ;color:#000000;background:#ffffff">compounds, precipitation, formation of gaseous substances.
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Let us treat ourselves at school as chemistry as one of the most difficult and therefore “unloved” subjects, but there is no point in arguing with the fact that chemistry is important and significant, because the argument is doomed to failure. Chemistry, like physics, surrounds us: it molecules, atoms, of which they consist substances, metals, non-metals, connections etc. Therefore chemistry- one of the most important and extensive areas of natural science.
Chemistry–is the science of substances, their properties and transformations.
Chemistry subject are forms of existence of objects of the material world. Depending on what objects (substances) chemistry studies, chemistry is usually divided into inorganic And organic. Examples of inorganic substances are oxygen, water, silica, ammonia and soda, examples of organic substances - methane, acetylene, ethanol, acetic acid and sucrose.
All substances, like buildings, are built from bricks - particles and are characterized a certain set of chemical properties– the ability of substances to take part in chemical reactions.
Chemical reactions – These are the processes of formation of substances of complex composition from simpler ones, the transition of some complex substances to others, the decomposition of complex substances into several substances of simpler composition. In other words, chemical reactions- These are the transformations of one substance into another.
Currently known many millions of substances, new substances are constantly being added to them - both discovered in nature and synthesized by man, i.e. obtained artificially. The number of chemical reactions is unlimited, i.e. immeasurably great.
Let's remember the basic concepts of chemistry - substance, chemical reactions and etc.
The central concept of chemistry is the concept substance. Each substance has unique set of features– physical properties that determine the individuality of each specific substance, for example, density, color, viscosity, volatility, melting and boiling points.
All substances can be in three states of aggregation – hard (ice), liquid (water) and gaseous (steams) depending on external physical conditions. As we see, water H2O presented in all stated conditions.
Chemical properties substances do not depend on their state of aggregation, but physical properties, on the contrary, depend. Yes, in any state of aggregation sulfur S upon combustion forms sulphur dioxide SO 2, i.e. exhibits the same chemical property, but physical properties sulfur very different in different states of aggregation: for example, the density of liquid sulfur is equal to 1.8 g/cm 3 solid sulfur 2.1 g/cm 3 and gaseous sulfur 0.004 g/cm3.
The chemical properties of substances are revealed and characterized by chemical reactions. Reactions can occur both in mixtures of different substances and within a single substance. When chemical reactions occur, new substances are always formed.
Chemical reactions are depicted in general view reaction equation: Reagents → Products, Where reagents are the starting materials taken to carry out the reaction, and products - These are new substances that are formed as a result of a reaction.
Chemical reactions are always accompanied physical effects- it could be absorption or release of heat, changes in the state of aggregation and color of substances; the progress of reactions is often judged by the presence of these effects. Yes, decomposition green mineral malachite accompanied by absorption of heat(this is why the reaction occurs when heated), and as a result of decomposition, solid black copper(II) oxide and colorless substances - carbon dioxide CO 2 and liquid water H 2 O.
Chemical reactions must be distinguished from physical processes, which change only the external shape or state of aggregation 
tion of the substance (but not its composition); the most common are these physical processes, How crushing, pressing, co-fusion, mixing, dissolving, filtering the precipitate, distillation.
With the help of chemical reactions it is possible to obtain practically important substances that are found in nature limited quantities (nitrogen fertilizers) or do not occur at all ( synthetic medications, chemical fibers, plastics). In other words, chemistry allows us to synthesize substances necessary for human life. But chemical production also brings a lot of harm to the environment - in the form of pollution, harmful emissions, poisoning of flora and fauna, That's why the use of chemistry must be rational, careful and appropriate.
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