The van der Waals idea of pseudo associations and the critical compressibility factor

Abstract

The dimensionless value of critical compressibility factor in the van der Waals theory of gas-liquid critical point is a universal constant, Z c = 0.375. Experimentally measured values of this quantity for simple fluids are considerably smaller than the theory prediction. Van der Waals once assumed that this discrepancy can be removed by taking account of the impact of the molecular pseudo-associations on the fluid criticality but he did not complete a proper modification of his theory following up on this idea. The communication is devoted to the filling of this gap.

On the Singularity of the Liquid-Gas Coexistence Curve Diameter

“…To some extent, this consideration was done in Ref. [22]. Pseudoassociations of Van der Waals can be regarded as a prototype of Frenkel's heterophase fluctuations.…”

“…[14] for a number of fluids, we fitted the parameters and at the fixed values of the parameters¯and . In so doing, on the basis of estimates of the quantity¯for simple liquids [22], we took¯= 3. The parameter was taken to equal 0.8.…”