Freezing points and enthalpies of dilution of aqueous formic, acetic, propionic, and butyric acids. Free energies and enthalpies of solute-Solute interactions

Alex Harris, Peter T. Thompson, Robert H. Wood

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

Freezing-point depressions and enthalpies of dilution for aqueous solutions of the straight chain, aliphatic carboxylic acids, C1 through C4, have been measured. These data, together with the corresponding apparent molal heat capacities, have been used to calculate the pairwise free energy and enthalpy of interaction of undissociated acid molecules at 298.150K. As expected, the effect of dimer and triplet interaction increases with chain length, reflecting the hydrophobic nature of the hydrocarbon portion of the molecules. The group-interaction additivity principle of Savage and Wood applied to these results gives an excellent correlation and yields values of the group interaction parameters, Gi,j and Hi,j for the CH2 and COOH groups. These parameters confirm previous results for the interaction of polar and hydrophobic groups in water. The primary data have been fitted to the activity expansion equations of Wood, Lilley, and Thompson to yield values of dimer and trimer "sociation" constants and their temperature derivatives. This procedure allows for the simultaneous treatment of the dissociation effects of these acids as weak electrolytes together with their tendency to form associated clusters.

Original languageEnglish
Pages (from-to)305-324
Number of pages20
JournalJournal of Solution Chemistry
Volume9
Issue number5
DOIs
Publication statusPublished - May 1980

Keywords

  • activity expansion
  • carboxylic acids
  • enthalpies of dilution
  • Freezing points
  • group additivity principle
  • sociation constants
  • solute-solute interaction

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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