**STEKHIOMETRIYA** (Greek stoicheion a basis, an element + metreo to measure, measure) — the section of chemistry devoted to studying of quantitative ratios in to-rykh substance enter chemical interaction with each other, and also to rules of a conclusion of chemical formulas and writing of the equations of chemical changes.

C. and its laws are widely used in biochemical, clinical, sanitary and hygienic and pharmaceutical laboratories for calculations of results of analyses, at preparation of solutions of the set concentration, for calculation of exits of products of reactions, etc. The term «stekhiometriya» is entered into practice it. chemist Richter (J. Century of Richter, 1762 — 1807).

Carry to fundamental laws of S.: the conservation law of weight established by M. V. Lomonosov in 1748 and A. Lavoisier in 1789 (the mass of the substances reacting is equal to the mass of the substances which are formed as a result of reaction), the law of definite proportions established by the fr. chemist J. L. Proust in 1808 (the structure of this chemical connection is constant and does not depend on a way of receiving this connection), the law of multiple proportions formulated in 1803 by J. Dalton (if two elements form with each other several chemical connections, then the mass of one of elements falling in these connections on the same mass of other element belongs among themselves as small integers), the law of volume ratioes opened in 1808. Gay-Lussac (volumes of the reacting gases belong to each other and to volumes of light-end products of reaction as small integers), A. Avogadro's law opened by the ital. physicist A. Avogadro in 1811 (equal volumes of any gases taken at the same temperature and with an identical pressure contain the same number of molecules). Stoichiometric laws originally were open empirically and afterwards are output from original positions of the atomic molecular theory.

Knowing chemical formulas of mother substances and reaction products, it is possible to present this chemical reaction on the basis of stoichiometric laws in the form of the equation, in Krom not only the interacting substances, but also quantitative ratios between them are specified. E.g., reaction between sodium hydroxide and a chamois to - that is expressed by the equation: 2NaOH + H_{ 2 } SO_{ 4 } = Na_{ 2 } SO_{ 4 } + 2H_{ 2 } O, from to-rogo follows that 2 asking sodium hydroxide react with 1 moths a chamois to - you with education 1 asking sodium sulfate and 2 moths of water. In correctly written equation of reaction the number of atoms of each element in the left and right member of equation has to be identical. Such equations of chemical reactions are called the stoichiometric equations, and the numerical values facing chemical formulas of substance — stoichiometric coefficients.

**Bibliography:** Glinka N. L. General chemistry, page 17, M., 1980; With l e y about At. and Persons of T. The general chemistry, the lane with English, page 18, M., 1979.

*V. P. Mishin.*