Excess Gibbs Energy and Activities

Abstract

Besides the fact that the introduction of the activities permits, among other processes, to quantify chemical equilibria when the behaviors of the fluids of the studied system are not ideal, it must be noticed that it also constitutes a means to study nonideal solutions. Another process to study them is to use excess Gibbs functions which are experimentally accessible. For some authors, their handling would be the best and the easiest means to study real (that is to say nonideal) solutions and, even, to study equilibria between fluids. In particular, their measurement would provide the best way to detect an ideal (or not) character. These few lines are sufficient to induce the taking cognizance of the existence of interesting mathematical expressions linking excess functions and activities. As this matter of things stands, it is evident that it is a part of the purpose of this book to study the links between activities and excess Gibbs energy functions. They concern solutions of nonelectrolytes and those of electrolytes as well.

In this chapter, the determination of activities from excess Gibbs energies by using empirical relations is studied. It concerns essentially the solutions of nonelectrolytes, in particular the binary ones. The activity values are found from the excess Gibbs energies through least square regression processes, linear or not linear.