Polar Hard-Core Exponential-6 Intermolecular Potential Function for Determining the Thermodynamic Properties of Polar Gases

Abstract

In this study, the hard-core Exponential-6 (hard-core Exp-6) model has been modified for polar molecules by adding an electrostatic force term to the function. The parameters of this new potential function are optimized using the literature data on the second virial coefficients of 37 polar substances. The average error of the polar hard-core Exp-6 model for these 37 polar gases, over 993 literature data, was 3.33%. Furthermore, the Stockmayer potential, the original Exp-6, and a modified Kihara potential with dipole–dipole interactions have been compared for the same data, and the errors were 6.91, 4.34, and 4.46%, respectively. In order to evaluate the ability of the proposed model in predicting the properties of polar compounds, which were not used in the optimization of the model parameters, the third virial coefficients of 18 different polar gases, the compressibility factor of ammonia, and the enthalpies and entropies of ammonia were calculated with the polar hard-core Exp-6 model. Based on the various results, it is concluded that this new potential function has great capability in the prediction of the thermodynamic properties of polar gases.