An exact quasi-chemical equation for excess heat capacity with W-shaped concentration dependence

Abstract

A reliable equation for the excess heat capacity C V E at constant volume is derived from Guggenheim's quasi-chemical lattice theory of liquid mixtures for the case of equal-sized molecules, with the assumption that the interchange energy depends on the temperature. Using suitable parameters, a W-shaped concentration dependence for C V E is predicted. The availability of this exact quasi-chemical equation permits the study of the theoretical dependence of C V E on temperature and concentration, a comparison with previous approximate results and better analysis of the molecular meaning of the W-shapes found in the experimental excess heat capacities C P E at constant pressure. Moreover, within this theory, the long-wavelength limit of the Bhatia-Thornton concentration-concentration partial structure factor S cc(0) is also derived and its correlation with C V E or C P E is discussed.