화학공학소재연구정보센터
Journal of Chemical Thermodynamics, Vol.117, 242-247, 2018
A simplification of gas clathrate hydrate thermochemistry using the Thermodynamic Difference Rule (TDR). Part 2. General Hydrates
For Gas Hydrates, MpXq center dot nH(2)O, available experimental standard enthalpy of formation data, Delta H-f(o)(MpXq center dot nH(2)O, s), are fairly sparse and for standard Gibbs energy of formation, Delta(f)G(MpXn center dot H2O, s) and standard entropy, S-298(o)(MpXq center dot nH(2)O, s) has never been directly determined experimentally for any gas clathrate hydrate. Using the Thermodynamic Difference Rule, TDR we are, however, able to rectify this deficiency and provide three simple equations: [Delta H-f(o)(MpXq center dot nH(2)O, s)-Delta H-f(o)(MpXq,g)]/kJ mol(-1)=-295.7n (R-2=0.9998; N=6) [Delta(f)G(o)(MpXq center dot nH(2)O, s)-Delta(f)G(o)(MpXq,g)]/kJ mol(-1)=-242n [S-298(o)(MpXq center dot nH(2)O, s)-S-298(o)(MpXq,g)]/J K-1 mol(-1) approximate to 41n capable of providing reliable estimates of these thermodynamic quantities for the entire suite of clathrate hydrates, always provided that the corresponding data for the gas molecules, MpXq is known. As a result of these Difference Rule derived equations it emerges that the standard enthalpy, free energy and entropy of gas clathrate hydrates are, each, solely dependent on the number of moles of water, n, per formula unit. This is a new observation. The two enthalpies of dissociation of the hydrates for the processes (H = L + G): Delta H-diss=9.9n kJ mol(-1) and for (H = I + G): Delta H-diss'=3.9n kJ mol(-1) are also predicted by TDR to be a linear function of n. These results, which are discussed, are broadly consistent with those found in Part 1. A sample predictive calculation is given for Delta(f)G(o) and S-298(o) for CO2 center dot 6H(2)O. (C) 2017 Elsevier Ltd.