Transfer free energies and entropies of hydrobromic acid in ethanol + water mixtures: structure of aquo-alcoholic solvents

Abstract

Standard potentials (E^⊖) of the Ag–AgBr electrode obtained from e.m.f. values of the cell Pt, H₂(g, 1 atm)/HBr(m), solvent/AgBr–Ag at seven temperatures (10–40°C) have been used to compute standard free energies (ΔG^⊖_t) and entropies (ΔS^⊖_t) of transfer of HBr from water to ethanol + water mixtures containing 10, 20, 30 and 50 % by weight of ethanol. Variations of ΔG^⊖_t and TΔS^⊖_t with mole % alcohol have been compared in three alcohol + water systems with special reference to the effect of addition of alcohol on the three-dimensional structure of water. The entropy of transfer has been proposed as a sensitive probe for the elucidation of solvent structure.