Thermodynamics of the liquid system methane + propane

Abstract

The total vapour pressure of liquid mixtures of methane and propane has been measured as a function of composition at temperatures of 115.77 and 134.83 K. The activity coefficient of methane ƒ₁ and the excess Gibbs function of mixing G^E have been evaluated from the vapour pressure measurements, and the heat of mixing H^E and the excess entropy of mixing S^E have been estimated from the temperature dependence of G^E and compared with direct calorimetric values. Values of the excess thermodynamic functions have been calculated from a simplified version of the Flory theory of mixtures, with allowance for departures from the geometric mean (Berthelot) combining rule. Calculations show that these deviations are very small, but not negligible.