Reactions between ions in diluted solution

As the activity coefficient of an ion in solution depends primarily on its chaige, it is possible to use reasonable assumptions about the shape of the activated complex in order to estimate the activity coefficient more easily than for other types of reactions. 

In fact, each reactant is assimilated to a sphere, and two models have been proposed for a bimolecular reaction  

Curiously, these two models lead to qualitatively similar eonclusions. This proves again that the charge of ions is more important than their shape. 

We will first express the partial molar Gibbs free energy and use relation [11.12], eonsidering that this is the Gibbs free energy required for transferring an ion from a medium dielectric constant unity (equal to 1) to that of the solution. 

We assume that the ion is first released in a vacuum (D = 1). After Bom, the free 

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