Representation of the nonideality of electrolyte solutions using the cluster expansion theory

An explicit model for electrolyte solutions has been developed in terms of the cluster expansion theory, with which the osmotic coefficient and activity coefficient in the dilute concentration range can be predicted using the Pauling ionic diameter. In this model, the electrolyte solution is modeled as an ion gas immersed in a dielectric continuum, and the ion is represented as a charged hard sphere. Based on the Debye–Hückel theory, the effects of solvent and mean field of surrounding ions have been considered by virtue of an effective interionic pair potential. The applicability of the model as well as the effective pair potential adopted have been tested on a HBr solution and fourteen 1:1 haloid electrolyte solutions. The results suggest that the cluster expansion theory with incorporated effective pair potential can qualitatively predict the activity and osmotic coefficient of electrolyte solutions.