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), Δ sub H ° (298.15 K) = (301 ± 4) kJ·mol −1 and (59 ± 2) kJ·mol −1, respectively, were calculated.