We have measured at 25 °C the enthalpies of solution of acetic, benzoic, and valeric acids and of their potassium salts in water – tert-butyl alcohol mixtures containing up to 40% by weight of organic cosolvent. We have also determined these quantities for phenol, aniline, and pyridine in the same mixtures and for acetic acid, aniline, and pyridine in water–DMSO, water–acetone, and water–urea in the zone rich in water. Using these data we have calculated the standard enthalpies of solution, the corresponding transfer quantities, and the enthalpies of solvation. When the enthalpies of solution are difficult or impossible to measure we have shown that the enthalpies of transfer can be calculated from judiciously selected transfer quantities obtained from experimental measurements. In this way we have worked out the enthalpies of transfer of potassium phenolate and of anilinium and pyridinium chlorides and bromides in the various mixtures. The enthalpies of solvation have been separated into enthalpies of formation of a cavity in the solvent and enthalpies of interaction. From these last quantities an attempt at interpretation in terms of solute and aqueous-organic media structures was made. Keywords: enthalpies, solution, solvation, acids–bases, aqueous-organic media.
