A simple model for demonstrating the relation between solubility, hydrophobic interaction, and structural changes in the solvent

A simple model is solved to demonstrate the relationship between various thermodynamic quantities associated with certain processes in solutions and the corresponding structural changes in the solvent induced by these processes. In this specific model it is possible to derive exact expressions for the analogues of the dissolution, and of the hydrophobic interaction processes. Also the exact effect of these processes on the equilibrium composition of the solvent is computed. Following this, we proceed to treat the general case of processes in aqueous solution. The conclusion reached from both the specific model and from the general formalism is the following: If one defines the concept of the "structure of the solvent" (e.g., water) as an ensemble average, then the structural changes in the solvent induced by processes taking place in dilute aqueous solutions (such as solubility, dimerization, or any other association process) will not contribute to the standard free energy of the process, but may well contribute and even significantly to other standard quantities associated with that process.