The critical points of cubic equations of state for pure fluids

The critical point of an equation of state for a pure fluid generally has to be calculated from three coupled relations between the critical constants Vc, pc and Tc. It will be shown that for any cubic equation of state these relations may be decoupled in such a way that only one relation for Tc has to be solved, whereupon Vc and pc follow by direct substitution. For cubic equations with a Van der Waals-type repulsive term a second form of the solution is given. As examples the equations of Redlich and Kwong, of Ishikawa, Chung and Lu, and of Kumar are considered.