Thermodynamics of (water + hexamethylphosphoramide) mixtures: heat capacity properties in the temperature range between 283.15 K and 298.15 K at ambient pressure

Abstract The specific ( c p ) and molar ( C p ) heat capacities of the mixtures of hexamethylphosphoramide (HMPA, or h) with water (w) have been measured using an adiabatic calorimetry at T = (283.15, 288.15, 293.15, and 298.15) K and ambient pressure. Based on the results obtained, the excess molar heat capacities of the mixtures, C p E , as well as apparent molar heat capacities of each component, C p , ϕ , i (down to its infinite dilution, C p , i ° ), have been calculated. The C p E values are positive up to HMPA mole fractions being xh ≈ 0.9 and the dC p E / d T derivative undergoes a positive-to-negative sign inversion at xh = 0.33. Both concentration and temperature dependences of C p , ϕ , i have also a complex character. The correlations of molar heat capacity properties with volume-related those for (H2O + HMPA) at the same temperatures have been discussed, too.