Vapor Pressure and Heat of Vaporization. Pre-lab questions. Vapor pressures as a function of temperature for either liquids of solids can be closely fit by the simple equation 1. In (vapor pressure)--AT B where A = ì¨,aporzation/R for liquids or ì!sublimation/R for solids, B is a constant characteristic of the system and R is the ideal gas constant. Plot the following data for liquid water in this form and determine the value for ÎHap from the slope of the line. (Don't forget that R can be expressed in many different units.) How does your value compare with the literature value? P (torr) 23.8 31.8 149 355 760 P (torr) T (K) 263 268 273 283 293 298 303 2.15 3.16 4.58 9.21 17.5 353 373 23333