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

The vapor pressures of solid AlF(3) and AlCl(3) 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 AlF(3) and AlCl(3), respectively. Treating the measured vapor pressures by the second- and third-law methods, the average standard enthalpies of the sublimation of 1 mol solid AlF(3) and AlCl(3) to AlF(3)(g) and Al(2)Cl(6)(g), Delta(sub)H degrees (298.15 K) = (301 +/- 4) kJ.mol(-1) and (59 +/- 2) kJ.mol(-1), respectively, were calculated