The Effect of Temperature on the Solvation of Alkanes, Alkanols, and Water

Collin Wick, University of Minnesota

Gibbs Ensemble Monte Carlo simulations were carried out to determine the free energies, enthalpies, and entropies of transfer at a variety of temperatures for n-octane, 1-butanol, and water. The Transferrable Potentials for Phase Equilibria force field was used to model n-octane and 1-butanol, and the OPLS TIP5P model was used to model water. The directly determined enthalpies were compared to enthalpies calculated from the Van’t Hoff equation. The Van’t Hoff equation was shown to do moderately well for octane and butanol, but not for water. The shortcomings of the Van’t Hoff equation originate with the approximation that the enthalpy be constant with temperature, which was not found in the simulations. Also, it was found that the changes of solvation with temperature were driven by solute enthalpy differences, and not entropy.

Abstract Author(s): Collin D. Wick, J. Ilja Siepmann, and Mark R. Schure