Chemical reaction equation - conditional chemical reaction record

To simplify the recording of chemical processes and their better perception The reaction equation is used. It is a conditional record of the interaction of substances among themselves and, as a consequence, the formation of new products. With this schematic "image", to maintain the law of conservation of mass of matter, use numerical coefficients. This description of chemical reactions with the help of numbers and symbols was proposed in 1615 by Jean Begun. Later, after the discovery of the laws of stoichiometry, quantitative values began to be used.

The chemical equation of the reaction is written as:

1. In the left part of the schematic "image" are the substances between which there is interaction, between them is the sign "+". In the left part are the reaction products, i.e. New compounds that have formed. Between the left and right parts is an arrow indicating the direction of the reaction. For example, C + E → CE.
2. Then the coefficients are set, the task of which is to "level", i.e. To make the quantity of each type of atoms before the reaction equal to the number of atoms after it. Thus, the "law of conservation of mass" "works". For example, 2HCl-H ₂ + Cl ₂ .

There is a kinetic equation of the reaction, which expresses the dependence of the rate of the chemical process on the concentration of substances that have entered into the interaction. A simple such reaction, going into one stage, is schematically written as: V = k [A ₁ ] n ¹ * [A ₂ ] n ² , where

V is the reaction rate;

[A ₁ ], [A ₂ ] are the concentrations of substances;

K is the rate constant of the reaction, which depends on the nature of the substances interacting and the temperature;

N ¹ , n ² is the order of the reaction.

If the reaction goes on in several stages, then they form a system of kinetic equations, each of which will be described separately.

Also, the ionic equation of the reaction is an individual species, which, when compiled, has singularities, since The substances recorded in it are in the form of ions. Such a schematic record of the chemical interaction is typical only for substitution and exchange reactions , in aqueous solutions or alloys, during which a precipitate is formed, poorly dissociating substances (water) or gas is released. For example: hydrochloric acid and potassium hydroxide enter the chemical reaction, salt and water are formed.

HCl + KOH-KCl + H ₂ O

We record these substances in the form of ions, with the exception of water, because It does not dissociate. Such a reaction equation will be called full ionic.

H ⁺ + Cl ^- + K ⁺ + OH ^{- -} K ⁺ + Cl ^- + H ₂ O

Now in this scheme, by the principle of similarity, from the right and left sides we "cut" the repeated ions and get:

H ⁺ + OH ^- - H ₂ O.

Also, oxidation-reduction reactions, characterized by a change in the degrees of oxidation of atoms, will have peculiarities in the compilation of a schematic record. It is necessary to determine the atoms that have changed the degree of oxidation, and make up an electronic balance, on the basis of which then to arrange the coefficients.

Thus, the chemical equation of the reaction is a schematic record of the whole complex process of the formation of new substances by decomposition, combination, substitution and exchange. It also provides qualitative and quantitative information on reacting substances and reaction products.