A model for interaction of nonpolar molecules differing in size and shape

Thermodynamic properties of pure nonpolar liquids, including long‐chain hydrocarbons are obtained accurately by derivation from an analytical partition function and the corresponding‐states principle. The characteristic parameters are interpreted in terms of group contributions in order to relate them to the structure of the molecule and further to provide a useful basis for a predictive theory of the properties of mixtures. The model for interactions between molecules takes into account the influence of molecular shape on the number of nearest neighbors and the limited number of interacting groups in a binary intermolecular contact. One obtains energy and size characteristic group interaction parameters related to those derived from London's formula and a unique function of the number of carbon atoms to characterize the shape of the molecules. Using these results obtained from pure liquids, one can predict at the same time excess enthalpies and Gibbs free energies of mixtures.