Non-unique reaction equilibria in non-ideal systems

Illustrations are given of non-ideal solutions of chemically reactive substances which display more than one equilibrium state, i.e. more than one relative minimum of Gibbs free energy. Simple cases are pairs of minima in symmetric regular solutions and unsymmetric Margules and van Laar solutions of two isomers in reactive equilibrium. The accessibility of the absolute minimum is discussed. Implications are pointed out for the general problem of calculating equilibrium states in non-ideal reaction systems.