Excess partial molar enthalpies of water in water–tert-butanol mixtures

Abstract

The excess partial molar enthalpies of H2O, HmE(H2O) in water–tert-butanol mixtures were measured at 30.00, 36.75, and 40.45°. Using the values of HmE(TBA) of the previous work (Y. Koga, Can. J. Chem. 66, 1187 (1988)), the excess (integral) molar enthalpies of the solution, HmE, were calculated at 30.00 °C, and compared with the literature values. The comparison was satisfactory. From the literature values of the excess free energy, the chemical potentials of each component were evaluated for the range, xTBA > 0.1. With the measured values of the excess partial molar enthalpies, the excess partial molar entropies were also calculated. These partial molar thermodynamic quantities and their dependence on temperature and composition clearly support the following views: (1) in the intermediate region, 0.1 < xTBA < 0.5, the system is very close to a critical demixing, and (2) in the TBA-rich region, xTBA > 0.6, TBA molecules in the solution are in almost the same environment as in the pure liquid, while H2O molecules lose the hydrogen bond network completely and are dispersed in the TBA liquid structure.