Thermodynamic perturbation theory for mixtures of spherical and tetrahedral molecules

Abstract

A Weeks-Chandler-Andersen type perturbation theory (PT) is presented for the Helmholtz energy of liquid mixtures consisting of spherical and tetrahedral molecules. Use is made of a hard fused sphere anisotropic reference system. The excess properties g ^E, h ^E and v ^E are predicted for the mixtures CS₂/CCl₄ and Ar, Kr, Xe, CH₄/CF₄. CCl₄ and CF₄ are modelled as tetrahedrons, the other substances are treated as spheres. The consequences of molecular shape on the prediction of excess values is discussed. The tetrahedrons are modelled with and without an additional interaction site at the centre of mass. The influence on the excess properties turned out to be small. For the system Xe/CF₄ the shape influence on the concentration dependence of the excess properties is small, and is compared with experiment. For the CF₄ mixtures it is shown that unlike interaction parameters determined in the liquid phase predict the excess virial coefficients almost within the experimental accuracy.