Temperature dependence of the excess molar heat capacities for alcohol-alkane mixtures. Experimental testing of the predictions from a two-state model

Abstract

A simple association model for alcohol-alkane mixtures, based on the idea that only two energy states are accessible to alcohol molecules in the pure and in the solution states, predicts complex temperature and alcohol concentration dependences of the excess molar heat capacity, C-p.m(E). These predictions are tested through the accurate measurement of pure component and solution heat capacities in the 278.15-338.15 K temperature interval. These measurements were performed at low, equimolar, and high alcohol concentrations for a linear alcohol (1-butanol) and a branched alcohol (3-methyl-3-pentanol) mixed with n-decane and with toluene. The qualitative predictions from the two-state model are corroborated by the data. According to this model, the very different C-p.m(E) behaviors found for the different systems arise simply through the change in hydrogen bonding Gibbs energy occurring on moving from the linear to the branched alcohol and in going from the inert n-decane to the aromatic toluene.