Enthalpy of dissociation and cavity occupation

In this section, enthalpy evidence for structures I, II, and H is presented to suggest that guest size fixes the heat of dissociation. That is, heat of dissociation for the hydrate structure is determined by the cavity occupied. The initial work for si and sll was presented by Sloan and Fleyfel (1992), with a critique by Skovborg and Rasmussen (1994) and a reply by Sloan and Fleyfel (1994). Similar results for sH are presented by Mehta and Sloan (1996b). 

To a fair engineering approximation AH is not only a function of the hydrogen bonds in the crystal, but also a function of cavity occupation. Because the Clausius-Clapeyron equation determines the heat of hydrate formation by the slopes of plots of In P versus 1/T, one may easily determine relationships between heats of dissociation. 

Mehta and Sloan (1996b) present data in Table 4.9 for 19-structure H hydrates formers along uni variant four-phase lines. With only three exceptions, the enthalpy of hydrate formation is 79.5 kJ/mol 7%. In each case, methane occupies the 512 and the 435663 cages while the larger guest occupies the 51268 cage. 

O Natural [] Natural O Natural A Natural Natural Natural 0 Natural V Natural 

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