Gas hydrates containing argon, krypton and xenon: kinetics and energetics of formation and equilibria

Abstract

Inert gases have been found to react fully and rapidly with ice crystals, with a mixture of crystals of chloroform and of ice, or with pre-formed chloroform hydrate, provided the crystals were rapidly agitated with small steel ball-bearings. Reaction still occurred readily at temperatures as low as-183°C (argon and ice). The above finding made it possible to measure sorption isotherms in hydrates of types I and II over a range of pressures and at various temperatures. For the type II chloroform hydrate heats of intercalation, ∆H, of rare gases were evaluated from the temperature coefficients of the isotherms, which closely followed Langmuir’s isotherm equation. For Ar, Kr, and Xe, ∆H was respectively -6.1, -6.7 and -7.9 kcal/mole respectively. In the type I hydrates the sorption isotherms necessarily terminated at the dissociation pressures. These pressures were measured over a range of temperatures. From them overall heats of reaction, ∆H₁, between ice and inert gas were derived for degrees of occupancy of the intracrystalline cavities of over 90%. For Ar, Kr and Xe ∆H₁ was -2.94, -3.98 and - 5.77 kcal/mole respectively. Corresponding heats of intercalation estimated indirectly were -5.5, -6.0 and -7.4 kcal/mole, and the averaged heat of formation of the empty host lattice of type I from ice was estimated as 0.35 ± 0.10 kcal/mole H₂O. The results have been discussed theoretically from viewpoints of energetics and equilibria, and of the significance of dP/dT in Clapeyron’s equation. Equilibria in the chloroform hydrates show deviations from the ideal statistical thermodynamic treatment of clathrate solid solutions, the best result being obtained for Xe and the worst for Ar.