Thermodynamics of the hydration of non-polar substances

We re-examine the numerical value and physical significance of T-S, the temperature where the entropy of transfer Delta(L)(W)S from the pure hydrocarbon liquid into water is zero, It is shown that the numerical value of T, depends on the convention adopted for calculating Delta(L)(W)G from solubility data at 25 degrees C and on the Delta(L)(W)C(P), fitting function. It is concluded that the interpretation of T, as the temperature where hydration ceases cannot be sustained. As previously reported [R.L. Baldwin, N. Muller, Proc. Natl. Acad. Sci. USA, 89 (1992) 7110], hydration must vanish at a temperature T' > T-S, where its experimental manifestation, i.e., Delta(L)(W)C(P), is zero. We discuss the concept of water relaxation around a non-polar solute molecule and its relation to the hydration process. (C) 1998 Elsevier Science B.V.