Thermodynamic functions of hydration of alkali metal and halide ions

Abstract

On the basis of some simple and general hypotheses about the hydration process, a range of values are defined for the thermodynamic functions of hydration for alkali metal ions and the halide ions.

The assumptions are: (I) for any ion the entropy of hydration is always negative; (II) there is a direct correlation between entropy and enthalpy of hydration independent of the sign of the charge on the ion; (III) for large ions the hydration process is dependent only on the radius.

A criterion of symmetry is applied, for isoelectronic couples, to the sequence of the values of the thermodynamic functions, which leads to a definition of functions for the hydration of the proton: –5.0 cal mol^–1 K^–1 for the partial gram-ionic entropy, –266.0 kcal mol^–1 for the enthalpy and –256.7 kcal mol^–1 for the free energy at 298.15 K.