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

The vapor pressures of gallium trihalides GaF3, GaCl3, and GaI3 were measured by a torsion effusion apparatus, and their temperature dependences fit the following equations: 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 GaF3, GaCl3, and GaI3, respectively. Both GaF3 and GaI3 vaporize practically congruently in monomeric form while GaCl3 is in dimer form. Treating the vapor pressures by second- and third-law methods, the selected standard enthalpies ΔH°(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 GaF3, GaCl3, and GaI3, respectively, were obtained.