Abstract
Physical meanings of the terms in the basic formulas for solution-thermodynamic quantities are reexamined. It is confirmed that the unitary term corresponds precisely to the unitary process of Gurney that a new solute molecule is introduced into a fixed position in solution, while the communal term describes the entropy increase caused by the increase in the number of positions available to the added molecule due to its liberation from the fixed position. The enthalpy-entropy compensation law holds for the indirect effects of the added solute on solvent not including the direct effects of solute-solvent interactions. Based on these results, the origin of the additional molar-volume-correction term in the formula of Sharp et al. [Biochemistry 30 (1991) 9686] for the unitary transfer free energy is elucidated to show that their expression corresponds to a process different from the unitary process of Gurney.
