Chapter Ten - Hydration Energies of Atoms and Small Molecules in Relation to Clathrate Formation

Abstract

Publisher Summary The mechanism by which only atoms or (usually hydrophobic) small molecules, when immersed in (cold) water, can become individually encaged within a sphere of hydrogen-bonded water molecules, thus forming clathrate hydrates, is due to the fact that such clathrate configurations comprising only one guest atom or small molecule are surface thermodynamically favored. This is because in these special cases of single small guest atoms or small molecules, the free energy of cohesion between the (cold) water molecules encircling the guest atom or molecule, superimposes itself on, and in so doing amplifies, the free energy of hydration of each separate atom or small molecule, which then becomes firmly encaged as an individual clathrate hydrate. With larger hydrophobic, or partly hydrophobic molecules or particles only contributes to the attraction driving the hydrophobic effect, thus causing the precipitation, flocculation or agglomeration of larger hydrophobic molecules or particles, when immersed in water. An alternative explanation of the stability of clathrates may also be considered, to the effect that once a hydrophobic atom or small molecule is surrounded by a watercage, or clathrate, the exterior of such an aqueous clathrate (c) may be treated as a sphere of which the distal, aqueous part, interfaces with the surrounding bulk water (w).