Perturbed hard sphere equations of state of real fluids—II. Residual parameter ap of non-polar liquids

Abstract

Using the accurate Baker-Fisher-Watts potential, the dipole-dipole-dipole three-body potential, and the EXP approximation, the residual term a p of a perturbed hard sphere equation of state for argon has been calculated and compared with experimental data. Individual contributions to a p , as well as to the pressure, have been assessed and compared with simple analytical expressions currently available. It is shown that (1) the frequently used high temperature approximation alone yields, necessarily, a very poor equation of state and (2) that an accurate perturbed hard sphere equation of state must contain additional terms having their origin in non-additive three-body interactions and certain higher-order perturbation contributions.