Simple model for second virial coefficients which includes angular coordinates. Calculation of second virial coefficients for hydrocarbons and their mixtures

Abstract

A simple square well potential model for calculating the second virial coefficients of hydrocarbons is presented. The model includes, in a rough way, both internal and external angular coordinates, thus accounting for the major steric and entropic effects of molecules which are not spherically symmetric and which have internal rotational degrees of freedom. Methane, ethane and neopentane were used to establish the potential parameters. The second virial coefficients of eleven other hydrocarbons and hydrocarbon mixtures were calculated from these parameters. Calculated values differed from the experimental values by an average of 13 %. Adjusting the parameters for a good fit of all of the data gave deviations of < 10 % except for pentane which was high by 25 %.