Solubility of natural gases in water

C L2 G transfer from gas to liquid, standard state, fugacity = 101.3 kPa. 

Entropy is a measure of disorder. The largest negative entropy of solution in Table 3.1 is generally considered as evidence of the creation of structure (increased order) within the body of water. More recently it has been suggested that the creation of a cavity can explain the entropy decrease. Large heat capacity changes also indicate the structuring effect of the solute on the water molecules. The size of the solute molecule has a substantial effect on solubility. 

In a review of the thermodynamics of water, Franks and Reid (1973) showed that the optimum molecular size range for maximum solubility was similar to hydrate stability. Franks and Reid noted, this is not intended to imply that long-lived clathrate structures exist in solution—only that the stabilization of the water structure by the apolar solutes resembles the stabilization of water in a clathrate lattice. Glew (1962) noted that, within experimental error, the heat of solution for ten hydrate formers (including methane, ethane, propane, and hydrogen sulfide) was the same as the heat of hydrate formation from gas and ice, thereby suggesting the coordination of the aqueous solute with surrounding water molecules. 

The most popular explanation of such changes in solubility stems from the hypothesis of Frank and Evans (1945), that the presence of the solute molecule causes an increase in the order of bulk water molecules, with the formation of water hydration shells around solute molecules. This is with the caution that such ordering 

The sharing of imperfect cluster faces of the clathrate-like clusters can be viewed as a thermodynamic tendency to minimize the negative entropies of solution. The tendency for face- or edge-sharing of individual solvation clusters, as Stillinger (1980) pointed out, is the same as the tendency for clustering of pure supercooled water. 

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