The Second Virial Coefficients of Some Cyclic Hydrocarbons

This paper reports some measurements of the second virial coefficient B of cyclopropane in the temperature range 300 to 400°K . It also gives some values of B for cyclohexane and benzene, derived from critical analyses of the published vapour densities and P-V-T properties of these gases between 300 and 650°K . In each case the results have been fitted to the relation B = α + β/T + γ/T2 + δ/T3 The following conclusions can be drawn : (i) The values of B for benzene and cyclohexane are consistent with the effects of pressure on the enthalpies and heat capacities of the gases. (ii) cycloHexane and benzene show large and almost equal deviations from the law of corresponding states for monatomic gases, but cyclopropane shows a much smaller deviation. (iii) It is impossible to fit the second virial coefficients of benzene and cyclohexane to the theoretical curve for a Lennard-Jones (12,6) gas. But they can be fitted to the curve for a (28,7) gas, and the associated force constants are physically reasonable. It appears that the interaction potential for cyclopropane molecules is intermediate between the (12,6) and (28,7) potentials.