Excess Gibbs free energy in methanol + acetic acid and ethanol + acetic acid

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Abstract

Total vapour pressures have been measured by the isoteniscope method for methanol + and ethanol + acetic acid at 308.15 and 318.15 K. Activity coefficients for the liquid phase and compositions of the vapour phase were evaluated by numerical integration of the Gibbs-Duhem equation taking into consideration the dimerization of acetic acid in the vapour phase. The mixtures are both characterized by negative deviations from ideality. The excess Gibbs free energy GE is almost symmetric about mole fraction x = 0.5, with minimum values of -235 and -215 J mol-1 for methanol + acetic acid and -184 and -132 J mol-1 for ethanol + acetic acid at 308.15 and 318.15 K respectively. The negative values of GE indicate the formation of hetero-complexes-due to intermolecular hydrogen bonds-and this effect is stronger in methanol + acetic acid than in ethanol + acetic acid.

Original languageEnglish
Pages (from-to)181-186
Number of pages6
JournalJournal of Chemical Thermodynamics
Volume12
Issue number2
DOIs
StatePublished - 1 Jan 1980

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