Thermodynamic Properties of van der Waals Dimers and Trimers of Nonpolar Gases and Their Correlation with Lennard-Jones Potential Well Depths.

Abstract

A method of unifying the equilibrium thermodynamic properties ΔHo and ΔGo relating to the van der Waals dimers and trimers of 15 nonpolar gases (He-Xe, H2, D2, CH4, CF4, ethene, ethane, CO2, SF6, propane, and neopentane) is described. Values of ΔHo and ΔGo, obtained at the reduced temperature Tr = 0.7, show good correlation with the respective Lennard-Jones pair potential well depth, calculated from the monomer critical temperature and the acentric factor. Such relationships present the opportunity to estimate the van der Waals dimer and trimer thermodynamic properties of other nonpolar molecules, and examples of seven such applications are given. It is found that the enthalpies of dimerization and trimerization of the 15 gases are about 21 and 29% of the respective condensation enthalpies, providing information about the thermodynamics of small clusters in relation to liquefaction.