Structural Approach to the Solvent Power of Water for Hydrocarbons; Urea as a Structure Breaker

TLDR: In this article, a skeleton model was proposed for the solubility of urea to water, where water was represented as a two-species mixture of dense and bulky constituents and the dissolved hydrocarbon is represented as dissolving separately in these constituents.

Abstract: The finding of Wetlaufer et al., that addition of urea to water increases the (mole fraction) solubility of hydrocarbon gases (except methane) while making them dissolve with a smaller evolution of heat, is interpreted as a primarily statistical phenomenon. For this purpose, it is treated in terms of a skeleton model in which not only is water represented as a two‐species mixture of dense and bulky constituents but the dissolved hydrocarbon is represented as dissolving separately in these constituents, as if it were distributed between two phases, i.e., between a quasiclathrate solution in the bulky constituent and a quasilattice or “regular” solution in the dense one. Added urea is pictured as being able to enter only one of the solutions, the quasilattice one in the dense water, with the result that it acts as a structure breaker. A statistical‐thermodynamic analysis of this model leads to equations for the chemical potentials and the partial molal enthalpies and entropies of the hydrocarbon and the ure...