To simplify the recording of chemical processes and their better perception reaction equation is used. It is a conditional record of the interaction of substances among themselves and, as a result, the formation of new products. With such a schematic "image", in order to comply with the law of conservation of mass of a substance, numerical coefficients are used. Such a description of chemical reactions using 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 reaction equation is written as follows:
- On the left side of the schematic “image” are substances between which there is an interaction, a “+” sign is placed between them. On the left side are reaction products, i.e. new compounds that have formed. Between the left and right parts there is an arrow indicating the direction of the reaction. For example, C + E → CE
- Then, the coefficients are set, the task of which is to “level”, i.e. so that the number of each type of atom before the reaction is 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 a chemical process on the concentration of substances that have interacted. A simple such reaction, proceeding in one stage, is schematically written as follows: V = k [A
1 ] n
1 * [A
2 ] n
2 , where
V is the reaction rate;
[A 1 ], [A 2 ] - the concentration of substances;
K is the reaction rate constant, which depends on the nature of the interacting substances and temperature;
n 1 , n 2 - reaction order.
If the reaction proceeds in several stages, then they form a system of kinetic equations, each of which will be described separately.
Also a separate type is the ionic reaction equation, which, when compiled, has features, because the substances recorded in it are in the form of ions. Such a schematic representation of the chemical interaction is typical only for
substitution and exchange
reactions in aqueous solutions or alloys during which a precipitate forms, poorly dissociating substances (water) or gas is released. For example: hydrochloric acid and
potassium hydroxide enter a chemical reaction
, and 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 she 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, on the right and left sides we “reduce” the repeating ions and we get:
H + + OH - - H 2 O.
Also, redox reactions, characterized by a change in the oxidation states of the atoms, will have features in the preparation of a schematic notation. It is necessary to determine the atoms that have changed the degree of oxidation, and create an electronic balance, on the basis of which then to arrange the coefficients.
Thus, the chemical reaction equation is a schematic representation of the entire complex process of formation of new substances by decomposition, compound, substitution and exchange. It also provides qualitative and quantitative information about reactants and reaction products.