Vapor Pressures of Gallium Trifluoride, Trichloride, and Triiodide and Their Standard Sublimation Enthalpies

The vapor pressures of gallium trihalides GaF(3), GaCl(3), and Gal(3) were measured by a torsion effusion apparatus, and their temperature dependences fit the following equation: log(p/Pa) = (14.30 +/- 0.30) - (12600 +/- 200)/(T/K) (from 808 to 958 K), log(p/Pa) = 13.80 - 3800/(T/K) (from 289 to 308 K), and log(p/Pa) = (14.00 +/- 0.50) - (5130 +/- 150)/(T/K) (from 345 to 401 K) for GaF(3), GaCl(3), and Gal(3), respectively. Both GaF(3) and Gal(3) vaporize practically congruently in monomeric Form while GaCl(3) is in dimer form. Treating the vapor pressures by second- and third-law methods, the selected standard enthalpies Delta H degrees(298 K) = (252 +/- 4) kJ.mol(-1), (89 +/- 2) kJ.mol(-1), and (100.5 +/- 2.0) kJ.mol(-1) associated with the Sublimation of GaF(3), GaCl(3), and Gal(3), respectively, were obtained.