VAPOR-PRESSURE AND STANDARD ENTHALPIES OF SUBLIMATION OF IRON DIFLUORIDE, IRON DICHLORIDE, AND IRON DIBROMIDE

Vapor pressures of solid FeF2, FeCl2, and FeBr2, were measured by the torsion and Knudsen methods and the following equations, valid in the reported temperature ranges, were derived: log{p(FeF2)/kPa} = 10.58 +/ - 0.20 - (13740 +/- 200)(K/T) (958-1178 K), log{p(FeCl2)/kPa} = 10.95 +/- 0.30 - (10390 +/- 300)-(K/T) (693-866 K), and log{p(FeBr2)/kPa} = 11.09 +/- 0.20 - (10320 +/- 250)(WT) (655-833 K). The following standa rd sublimation enthalpies were determined by second- and third-law tre atment of the vapor pressures: Delta(sub)H degrees(298 K) = 271 +/- 2, 204 +/- 4, and 208 +/- 2 kJ . mol(-1) for iron difluoride, dichloride , and dibromide, respectively.