From Big Medical Encyclopedia

CHEMICAL EQUILIBRIUM — the condition of a reaction system, at Krom the reversible chemical change proceeding in it goes with identical speeds in two opposite directions owing to what the structure of a reaction system remains to constants. Many biochemical processes represent reversible chemical tests therefore the chemical processes proceeding in an organism can be considered as a continuous number of removals of R. x.

If the reversible test proceeds according to the symbolical equation aa + bB ⇆ mM + nN, then the speed of the forward reaction going from left to right decreases eventually since concentration of reagents decrease; speed of the back reaction going from right to left increases owing to increase in concentration of reaction products; when speeds of forward and back reaction become equal each other, R. is established x. Thus, R. x. comes not owing to the termination of chemical processes in a reaction system, and as a result of equality of speeds of forward and back reaction, i.e. chemical balance is dynamic, or mobile, balance.

Each reversible test is quantitatively characterized by a constant of chemical balance To (see. the Operating masses the law ). Size K depends by nature reactants, temperature, by nature solvent (if the reversible test proceeds in solutions), but does not depend on initial concentration of reactants and on catalysts. At change of the conditions defining R. x., it is broken, and in a reaction system there are processes leading to establishment of the new balance answering to the changed conditions. Direction of removal of R. x. it is qualitatively possible to define by Le Chatelie's principle, according to Krom change of one of the conditions defining R. x., causes the shift of balance in the direction. counteracting the made change.

See also Kinetics of biological processes .

Bibliography: Glinka H. L. General chemistry, page 185, M., 1980; Williams V. and Williams of X. Physical chemistry for biologists, the lane with English, page 60, etc., M., 1976.

V. P. Mishin.