Excess functions of non-ideal solutions

The thermodynamic characteristics of solutions, especially nonelectrolyte mixtures, are frequently expressed by means of excess functions. These are the amounts by which the free energy, entropy, etc., of the given solution exceed those of a hypothetical ideal solution of the same composition. 

The excess Gibbs free energy is closely related to the activity coefficients. The total Gibbs free energy of a solution is 

In this equation we substitute from (9 1) cund obtain 

Differentiating this expression at constant temperature we obtain dO =s RTZrti d In y -I- UTS In y dn.  

Under conditions of constant temperature and pressure the first term on the right-hand side is zero, as follows from the Gibbs-Duhem equation. Therefore 

---

Solutions are thermodynamically classified into perfect, ideal, and non-ideal solutions. This chapter discusses the characteristics of these solutions and define the excess functions of non-ideal solutions. Also examined are electrolytic solutions which contain dissociated ions. 

---