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 (cp) and molar (Cp) 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, CpE, as well as apparent molar heat capacities of each component, Cp,ϕ,i (down to its infinite dilution, Cp,i°), have been calculated. The CpE values are positive up to HMPA mole fractions being xh ≈ 0.9 and the dCpE/dT derivative undergoes a positive-to-negative sign inversion at xh = 0.33. Both concentration and temperature dependences of Cp,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.