An equation of state used to predict the behaviour of real gases based on the van der Waals’ equation of state. It describes the variation of molar gas volume and pressure with temperature for many substances in a cubic equation as:
The constants a and b are determined from critical point data. The factor α is related to reduced temperature as:
where ω is the acentric factor. Developed in 1976, it is also useful for predicting liquid densities and is widely used in the petrochemical industry. It was further modified by Stryjek and Vera in 1986 to improve the accuracy of the model. The Peng–Robinson-Stryjek-Vera (p. 277) (PRSV) equations of state feature an adjustable pure component parameter and a modified polynomial fit for the acentric factor, and can be used for polar substances.