A new representation for thermodynamic properties of a fluid

Abstract

It is proposed to consider the contribution of the nonisolated molecular pairs to the configurational Helmholtz energy, i.e., the quantity f*/RT−Bρ, where the product of the second virial coefficient B times molar density ρ covers the contribution of the isolated pairs. Especially illuminating is the difference function Δ = (f*/RT−Bρ)real fluid −(f*/RT−Bρ)hard body fluid. From the few examples given it seems that this difference function is of a general nature provided that the anisotropy of the hard bodies corrsponds to the anisotropy of the molecules of the real fluid. The difference function can be correlated empirically in a simple way and can be used for estimating thermodynamic properties at intermediate and low densities from high density results.