Thermodynamics of liquid mixtures of nitrous oxide and ethene

Abstract

Experimental determinations of the vapour pressures, molar volumes and heats of mixing are reported for liquid mixtures of ethene and nitrous oxide at temperatures close to the triple-point temperature of nitrous oxide (182.32 K). From these measurements the excess volume. Gibbs free energy and enthalpy are derived. The excess Gibbs energy and the excess enthalpy are found to be positive, almost symmetric functions of composition, with values at the equimolar composition of 168.9 J mol^–1 and 270.9 J mol^–1, respectively. The excess volume, on the other hand, is found to be negative and displays a highly skewed composition dependence, the minimum occurring at x_N2O≈ 0.96.

These results were examined theoretically by the use of a perturbation theory based on spherical reference molecules. The importance of using a full non-axial treatment of the quadrupolar interactions between constituent molecules of the mixture is demonstrated. The effect of contributions to the free energy from the quadrupole–dispersion, anisotropic–dispersion and shape forces is shown to be of considerable importance in predicting the excess enthalpy. None of the intermolecular potential models studied was able to reproduce the shape of the excess-volume curve.