Application of an Interstitial Model for Water to Aqueous Solutions

Application of an Interstitial Model for Water to Aqueous Solutions 

In this section, we extend the application of the interstitial model for water to aqueous solutions of simple solutes. This is the simplest model that contains elements in common with similar models worked out by various authors. This model can be solved exactly, and therefore, various general results of the mixture-model formalism can be obtained explicitly. In this respect, this model has also pedagogical value. 

The description of the model and the basic assumptions have been introduced in Sec. 2.4. To apply this model for aqueous solutions, we further assume that Ns solute molecules occupy the interstitital positions in the framework built up by the L-cules (Fig. 3.16). The new molecular parameter that is introduced in the application of this model to aqueous solutions is the interaction energy between the solute s and its surroundings, which we denote by Eg. 

The combinatorial factor in (3.6.2) is the number of ways one can place Nh H-cules and Ng solute molecules into NqNi holes. The summation is carried over all possible volumes of the system, which by virtue of the assumptions of the model is the same as a summation over all Ny. The condition Nh NqNi 

As in the case of the one-component system, we take the maximal term in the sum (3.6.2), from which we obtain the equilibrium condition  

---