Mixing rules for equations of state

Copeman, T. W., and Mathias, P. M., 1986. Recent mixing rules for equations of state. ACS Symposium Series 300, American Chemical Society, Washington, D.C., pp. 352-369. 

When the standard-state pressure is taken to be the mixture pressure P° = P), then these distinctions disappear and the three activity coefficients (5.5.5), (5.5.9), and (5.5.11) are the same. But when P P, the numerical values for these three activity coefficients can differ, though the differences are usually not significant at pressures below 10 bar. However, such differences can contribute to the complexity encountered when trying to use a model for activity coefficients as a basis for developing mixing rules for equations of state. 

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