Torsion Vapor Pressures and Sublimation Enthalpies of Aluminum Trifluoride and Aluminum Trichloride

The vapor pressures of solid AlF3 and AlCl3 were measured by the torsion-effusion method. Their temperature dependences fit the following equations: log(p/kPa) = (11.70 ± 0.20) − (14 950 ± 200)(T/K) (from (956 to 1113) K) and log(p/kPa) = (15.50 ± 0.30) − (6200 ± 200)(T/K) (from (321 to 378) K) for AlF3 and AlCl3, respectively. Treating the measured vapor pressures by the second- and third-law methods, the average standard enthalpies of the sublimation of 1 mol solid AlF3 and AlCl3 to AlF3(g) and Al2Cl6(g), ΔsubH° (298.15 K) = (301 ± 4) kJ·mol−1 and (59 ± 2) kJ·mol−1, respectively, were calculated.