Mixing rules (see also Combining rules).
van der Waals mixing rules
The van der Waals equation of state can be written as
For mixtures one replaces and with expressions that depend on the composition:
where is obtained from a fit.
See also 
- Related reading
- T. Y. Kwak and G. A. Mansoori "Van der waals mixing rules for cubic equations of state. Applications for supercritical fluid extraction modelling", Chemical Engineering Science 41 pp. 1303-1309 (1986)
- Kenneth R. Hall, Gustavo A. Iglesias-Silva, and G. Ali Mansoori "Quadratic mixing rules for equations of state: Origins and relationships to the virial expansion", Fluid Phase Equilibria 91 pp. 67-76 (1993)