Estimating the second virial coefficients of some real gas mixtures and related thermodynamic views

Using the Gaussian 2003 software and MP2 /6 – 311+ G method for the C2H4 : O2, CO:Cl2 and CO2:CO2 pairs and MP2/6-311++G** method for the CO2:H2O pair and B3lyp/6-31G method for the O2:O2 pair the optimized interaction energies between two considered pair molecules of studied gases(C2H4:O2, CO:Cl2, CO2:H2O, O2:O2 and CO2:CO2 pairs) as a function of the distances between the centers of two considered molecules were evaluated and the results were interpreted according to the Lennard – Jones equation. In addition, the second virial coefficient of each pair gas was calculated upon the appropriate equations of statistical thermodynamics. The resultant coefficients were almost comparable with those are available in the literature.