Entropy change in charge separation

Separation of charges according to eq. (1.11.1) causes an entropy change that can be theoretically predicted. Since entropy determines the variation of the Gibbs energy with temperature [(dG/dT)p = -5], and [(dAG/dT)p = -AS], it follows  

6) shows that we can calculate the entropy change of the charge separation if we know the temperature dependence of the relative permittivity of the dielectricum. The value of the differential quotient rveJdT)p is 

With 1 = 1 for an ion in vacuum, eq. (1.11.7) gave the solvation free energy of the ion. The Bom equation is not accurate, since the bulk dielectric constants (relative permittivities) are not valid in the immediate neighborhood of an ion. This is the reason why Bom inserted 2a instead of a in (1.11.7), the value closer to the effective radius. Other investigators tried to improve eq. (1.11.7), for example, Latimer and co-workers, but with a limited success. 

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