For dense polyatomic liquids (rgr; 2rgr;c), the anisotropic part of the intermolecular forces has remarkably little influence on the isothermal compressibility or on the partial molal volume for the case of mixtures; this is also the case for dilute gases at high reduced temperatures. Such behavior is shown to be predicted by a perturbation treatment in which these properties for the polyatomic fluid are expanded about the corresponding values for a fluid with isotropic intermolecular forces. For dense liquids (or dilute, high temperature gases), the perturbation terms in such series usually become negligible compared to the zeroth order term. This leads to corresponding states relationships for these properties, which have the same functional form as for fluids composed of simple isotropic molecules, such as argon. This prediction is confirmed by a comparison of isothermal compressibilities for polyatomic liquids with the values for argon at the corresponding state condition.
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