mass-law effect

At equilibrium, the product of the activities (or concentrations) of the reacting species is constant. Thus for the equilibrium:
α A + β B ⇌ γ C + δ D
K = C γ D δ A α B β
See also: common-ion effect, equilibrium
Source:
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1138