SOLUTIONS OF INERT GASES IN WATER

Data for the solubility in water of gases ranging from Ne to n-C4H10 are reviewed and compared with their solubilities in c-C6H12. Entropies in the two solvents are very different in amount and origin. A variety of explanations have been offered to account for the losses of entropy caused by dissolving neutral molecules in this already highly structured solvent. Most of them assume either that water molecules form more rigid structures around solute molecules, or else that water is a labile mixture of different structures. We regard such models as open to question and propose instead an explanation based upon the Pople model of water molecules all bonded together by the maximum number of flexible hydrogen bonds all participating equally in thermal energy. When inert molecules are introduced, we suggest that H bonds are deactivated or destroyed to an extent depending upon the total surface of the solute. The entropy of solution of nine gases to the same mole fraction accordingly varies linearly with the two-thirds power of their molal volumes at their boiling points. The losses of entropy that occur when equal surfaces of water and liquid higher alkanes unite to form interfaces show virtually the same dependence upon the molal surfaces of the alkanes as is shown by the gaseous alkanes. © 1968, American Chemical Society. All rights reserved.