Vapor Pressure and Heat of Vaporization of Molecules That Associate in the Gas Phase

© 2018 American Chemical Society. A model of the temperature dependence of the vapor pressure and the heat of vaporization of liquids whose vapors contain associates is presented for two cases: dimers and linear associates in the gas phase. The results are analytic generalizations of the Clausius-Clapeyron equation, valid with accuracy of 0.1%-1%, as demonstrated with 11 liquids: formic and acetic acids, methanol, ethanol, n-propanol, n-butanol, water, benzene, toluene, heptane, and isooctane. The model involves only readily available handbook parameters: the room-temperature heat of vaporization, vapor pressure, heat capacities, second virial coefficient, and heat of dissociation of the dimers in the gas phase.The authors acknowledge the funding and technical support from BP through the BP International Centre for Advanced Materials (BP-ICAM), which made this research possible. This research is partially funded by the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. J.K.N. thanks Trinity College and the Clarendon Fund of the University of Oxford for a Clarendon–Titley Scholarship