THE 2ND VIRIAL-COEFFICIENTS OF N-ALKANES AND THEIR MIXTURES FROM THE KIHARA CONVEX CORE INTERMOLECULAR PAIR POTENTIAL

The second virial coefficients for a series of C2 to C-8 n-alkanes and the second virial cross coefficients for their binary mixtures were c alculated as a function of temperature from the exact expressions deri ved for the Kihara rod-like molecules. The three parameters of the Kih ara pair potential, epsilon/k, sigma and l for the individual compound s were either used as determined from vapour-liquid equilibrium and sa turated liquid density data in a previous study or with epsilon/k adju sted to the second virial coefficient data. The results are accurate a lmost within experimental uncertainty estimates of the data. In the ca se of mixtures the second virial cross coefficients were calculated fr om a similar expression in which only the epsilon12/k parameter was ad justed whereas sigma12 = (sigma1 + sigma2)/2 and l1 and l2 of pure com pounds were employed. It appears that the correction factor to the geo metric mean combining rule for epsilon12/k is always less than and clo se to unity. Comparison with the values obtained from the Tsonopoulos generalized correlation reveals fair agreement between the characteris tic binary k12 parameters from the two methods.