Universal Equations for Saturation Vapor Pressure

*The Wagner equation and the modified Antoine equation are two of several that can be used to accurately estimate the vapor pressure of a saturated liquid, given the liquid’s critical temperature and critical pressure. To achieve accuracy, such equations use multiple empirical constants that are unique to each liquid, but these constants are not available for all liquids. This paper presents two universal equations that provide fairly accurate vapor pressures for a variety of liquids. Each equation uses empirical constants, but a single set of constants applies to a large number of liquids. The universality of the equations suggests that they would be useful in estimating the saturation vapor pressure of a liquid whose Wagner or modified-Antoine-equation constants are unknown.