P-V-T properties of methyl chloride at high temperatures and pressures

Abstract

"The equation of state of a gas describes the relation between the three variables pressure, volume, and temperature. Many equations have been proposed which accurately describe the p-v-T relations of real gases (3,4,5,8,18,20, 26,31,32,39,51,58,70,74,90). Some of these are purely empirical while others are derived from the intermolecular properties. A knowledge of the equation of state is necessary for obtaining equilibrium properties of pure substances. The volumetric behavior of non-polar gases may be described by the application of the principle of corresponding states, which has been successful in predicting compressibility factors and second virial coefficients for both pure gases and binary gas mixtures (19, 24, 25, 34, 35, 49, 54, 59, 63, 66, 67, 71). Polar gases deviate considerably from the principle of corresponding states, and require different treatment. Two methods have been used in predicting the second virial coefficient of polar gases. The first method uses statistical mechanics and an intermolecular potential function based on a physical model. The second method is based on a hypothesis, first proposed by Eucken (21), that polar gases undergo partial association due to dipole interaction or to hydrogen bonding, and that this is responsible for their deviation from the principle of corresponding states. This method of interpretation was originally applied by Alexander and Lambert to their results on acetaldehyde (1), and later by others to interpret the second virial coefficients (10,23,30,33,46,47). In this investigation the first approach was used to analyze the experimental second virial coefficient data. In this investigation, the Kihara core model was used to represent the geometry of a polar molecule. A permanent point dipole was placed in the core and used to represent the polar contribution to the molecular pair force field. Pople's perturbation method (68) was used to obtain an expression for the second virial coefficient of a polar gas. Numerical methods were then used to evaluate the potential parameters for nine polar gases. Derived thermodynamic properties of methyl chloride were also calculated from the calculated B(T) values for the modified Kihara potential and compared with those calculated from the p-v-T data."--Introduction.