Study on the Sublimation of Gallium Tribromide

The temperature dependence of the total vapor pressure of GaBr(3) measured by the torsion-effusion method over the temperature range (300 to 357) K is represented by the following equation: log(p/Pa) = (16.1 +/- 0.6) - (5250 +/- 200)(K/T). This compound Sublimes to the monomer and dimer species. From the temperature dependence of the dissociation, and the equilibrium constant of the dimer found in the literature, the partial pressures of both forms were evaluated from which the second- and third-law standard enthalpies of the sublimation reactions, GaBr(3)(s) = GaBr(3)(g) and GaBr(3)(s) = 1/2Ga(2)Br(6)(g), were calculated: Delta(sub)H degrees(298 K) = (92.5 +/- 2.0) kJ.mol(-1) and (50.5 +/- 2.0) kJ.mol(-1) for the monomer and dimer forms, respectively.