Equilibrium properties of molecular fluid mixtures

Abstract

The application of perturbation theory in which all tensor interactions are taken as a perturbation of the central potential to a multicomponent fluid mixture of nonspherical molecules of arbitrary symmetry is considered. The influence of angle-dependent pair interactions arising from permanent electric multipole moments, induced dipole moments, anisotropic dispersion and overlap forces, and three-body nonadditive interactions arising from dispersion and classical electric induction interaction between asymmetric molecules on the Helmholtz free energy, in some cases through the third-order of the perturbation theory, is evaluated. The theory is applied to binary mixtures consisting of (i) a component of spherically symmetric molecules and another of axially symmetric molecules and (ii) both components of axially symmetric molecules. Comparisons with experiments are made for Ar–N2, Ar–O2, Ar–CO, N2–O2 and N2–CO binary mixtures at zero pressure isobar and T=83.82 °K as a function of composition for excess Gibbs free energy and excess enthalpy. Agreement with experiment is very satisfactory for all the systems.