How do you calculate compressibility factor from an equation of state?

Compressibility factor Z = PV/nRT measures deviation from ideal gas. From EOS: rearrange to form cubic in Z (for cubic EOS like PR, SRK). PR equation: Z^3 - (1-B)Z^2 + (A-3B^2-2B)Z - (AB-B^2-B^3) = 0, where A = aP/R^2T^2, B = bP/RT. Solve cubic for Z: three roots possible (vapor Z largest, liquid Z smallest, middle root unstable). Use appropriate root for phase. For mixtures, use mixing rules to get a_mix and b_mix. Generalized correlations (Lee-Kesler) also give Z from reduced properties.