BEITRÄGE ZUR DARSTELLUNG VON THERMODYNAMISCHEN EIGENSCHAFTEN REINER FLUIDER STOFFE

Abstract

The contribution of the nonisolated molecular pairs to the configurational Helmholtz energy. i.e., the quantity K=f*/RT-Bp where B is the second virial coefficient, p the molar density has been im:estigated. We define the following two quantities for fluids consisting of spherical molecules or molecules like dumbells. The first is the difference function: .1 = K real fluid - K hard body fluid' the second is the modified van der Waals constant: A = -h - T I/ where z is the compressibility factor. Zh that for the corresponding hard body fluid. I/ the compactness factor. Isotherms of Ll and A can be simultaneously fitted in terms of the compactness factor using six constants. The mean percentage deviation is for A 0.18% the mean deviation for Lllies in the order ofmagnitude 0.001. A possibility is shown für approximating the above quantities: Ll and A in terms of temperature and compactness factor, i.e , for setting up an equation of state for calculating the compressibility factor and thermodynamic functions using 15 temperature-independent constants.