Chemical association in simple models of molecular and ionic fluids. II. Thermodynamic properties

A simple interpolation scheme (SIS) suggested in an earlier paper is used to obtain the excess Helmholtz free energy and the equation of state for the shielded sticky-shell model and the shielded sticky-point model of associative fluids. It is found that the equation of state under the SIS for a fully associated homonuclear dumbbell fluid is quite accurate as long as L*=L/σ≥0.8. For ionic association, the excess Helmholtz free energy in this work reduces to that of Bjerrum’s theory in the ideal limit. An analytical equation of state for associative ions is evaluated.