Second Virial Coefficients of Polar Gas Mixtures

Abstract

An empirical equation used by Keyes to represent the second virial coefficients of several polar gases is compared to a theoretical expression for the same quantity. The constants appearing in this equation are discussed in terms of intermolecular forces, and their relationship to analogous constants in the Beattie-Bridgeman equation for non-polar gases is examined. These considerations permit the construction of simple rules by means of which the second virial coefficient of any gas mixture may be calculated if the second virial coefficients and dipole moments of the pure component gases are known. The success of these rules is demonstrated by comparison with data on H2O–CO2, N2–NH3, and N2–H2O systems. In the case of N2–H2O mixtures (vapor-liquid equilibrium data) the agreement is not satisfactory at the higher temperatures. A rough method of including the effect of higher virial coefficients reduces, but does not remove, this discrepancy.