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.