Definition of equilibrium, chemical

Reversible processes (processes which may be made to proceed in the forward or reverse direction by the (infinitesimal) change of one variable, ultimately reach a point where the rates in both directions are identical, so that the system gives the appearance of having a static composition at which the Gibbs energy, G, is a minimum. At equilibrium the sum of the chemical potentials of the reactants equals that of the products, so that

[Delta] Gr = [Delta] Gr0 + RT ln K = 0

[Delta] Gr0 = -RT ln K

The equilibrium constant, K, is given by the mass-law effect.