The phase instability and critical point in a liquid mixture of an associating and inert component

The problem of phase instability in a binary mixture of an associating component with an inert component is analyzed from the standpoint of the theory of association equilibria. It is demonstrated that conditions of the spinodal and critical point for such a binary system are equivalent to those of the spinodal and critical point of a multicomponent mixture consisting of complex species arising by association (including nonassociated molecules). These conditions are formulated so as if species in this mixture did not participate in association and dissociation processes; configurational terms expressing changes in the content of the individual complexes depending on changes in total composition are included implicitly.