VAPOR PRESSURE AND MELTING POINTS OF XENON DIFLUORIDE AND XENON TETRAFLUORIDE

Vapor pressure measurements have been carried out on samples of pure xenon difluoride and xenon tetrafluoride. The preparation and purification of the samples are described as well as the apparatus with which the data for the two reactive fluorine compounds were obtained. For xenon difluoride, the following equation represents the experimental results between 273 and 388°K log Pmm = -3057.67/T - 1.23521 log T + 13.969736 The corresponding vapor pressure equation for xenon tetrafluoride valid between 275 and 390.25°K is log Pmm = -3226.21/T -0.43434 log T + 12.301738 In addition, the triple-point temperatures of the two compounds have been determined by a thermal arrest method. For xenon difluoride a triple-point temperature of 402.18°K was found, and for xenon tetrafluoride, 390.25°K. The enthalpies of vaporization at 330°K were derived from the vapor pressure equations and the following values were obtained: ΔHsub = 55.2 ± 0.8 kJ mole-1 for XeF2, and ΔHsub = 60.6 ± 1.0 kJ mole-1 for XeF4. The standard entropy of xenon tetrafluoride vapor at 298.15°K was calculated from the vapor pressure and heat capacity data and found to be 305.2 J deg-1 mole-1. This number is compared with the entropy calculated from molecular data. The entropy of solid xenon difluoride at 330°K was calculated to be 122.8 J deg-1 mole-1.