The Corresponding States Principle (CSP) manifests the existence of a universal relation between the dimensionless parameters of fluids. The original two-parameter CSP can be applied only to spherical molecules. Introduction of a third parameter in the original two-parameter CSP enhances the scope of CSP to include fluids whose fields deviate from spherical symmetry. The central problem in the use of CSP lies in the choice of the physically realistic characteristic parameters of substances. To extend the CSP to molecular fluids, the nonspherical nature of molecules is taken into account through the acentric factor of substances. The CSP may also be augmented with the critical compressibility of substances. In this respect, CSP based correlations between the critical compressibility and the acentric factor are relevant. Alkali metals exhibit considerable uniformity when their thermodynamic properties are expressed in a suitable dimensionless form. Microscopically, it implies that the form of the intermolecular potential is the same. Hence, the CSP based study if alkali metals is significant. This work deals with a CSP based study on the correlations of the critical compressibility and the acentric factor of cesium, rubidium and potassium. These correlations are established through a generalized van der Waals equation of state. This three- parameter equation differs from the known van der Waals equation of state by the modified expression for molecular pressure. It has been established that the critical compressibility factor has a parabolic dependence on the acentric factor of alkali metals. Moreover, cesium, rubidium and potassium are found to obey the single-parameter law of corresponding states, with the critical compressibility or the acentric factor as the thermodynamic similarity parameter.

Acentric Factor, Alkali Metals, Corresponding States Principle, Critical Compressibility Factor, Molecular Pressure, Fluid Phase Equilibrium