Vapor pressure and heat of vaporization of molecules that associate in the gas phase

Authors: Radomir I. Slavchov, Javor K. Novev, Sebastian Mosbach, and Markus Kraft*

  • A model of vapour-liquid 1-component equilibrium with vapour dimerization.
  • Predicts analytically vapour pressure, vaporization heat and dimer fraction vs. T.
  • No fitting - input is 6 standard handbook thermodynamic parameters only.
  • Reversely, accurate thermodynamic parameters obtained from vapour pressure data.
  • High precision for fuel components under cylinder conditions.

abstractA 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 iso-octane. 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.

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Keywords: Vapour pressure, Clapeyron equation, dimerization, hydrogen bond, carboxylic acid, virial coefficient

Associated Project: Engines

*Corresponding author:
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