Thermodynamics of n-alkane + dimethylsiloxane mixtures. Part 2.—Vapour pressures and enthalpies of mixing

Abstract

The total vapour pressures of mixtures of n-hexane and hexamethyldisiloxane have been measured by a static equilibrium method at 303.15, 309.15 and 315.15 K. At each temperature the derived equimolar excess Gibbs free energy is small and positive. The excess enthalpy at 298.15 K, as determined by direct calorimetry, has a skew-parabolic composition dependence and a positive equimolar value of 126 ± 2 J mol^–1. Theoretical excess functions for n-hexane + hexamethyldisiloxane are calculated from a one-fluid van der Waals model in conjunction with an experimental pure liquid reference substance; they agree well with experiment.