Vapor pressures and sublimation enthalpies of copper difluoride and silver(I, II) fluorides by the torsion-effusion method

The vapor pressures in equilibrium over CuF2, AgF2, and AgF were measured by the torsion-effusion method. CuF2 and AgF vaporized congruently. The temperature dependences of the vapor pressure of these compounds were found to fit the following equations: CuF2(S), log)/kPa) = (9.78 +/- 0.10) - (12690 +/- 100)(T/K) (from (884 to 1051) K) and AgF(l), log(p/kPa) = (7.83 +/- 0.20) - (10700 +/- 300)(T/K) (from (880 to 1074) K). Treating the vapor pressure data by the second- and third-law methods, the standard sublimation enthalpies of these compounds, Delta H-sub degrees(298 K) = (260 +/- 4) kJ.mol(-1) and (240 +/- 10) kJ.mol(-1) for CuF2 and AgF, respectively, were calculated. In the covered temperature range (from (655 to 776) K), AgF2 decomposes into fluorine and solid or molten AgF so that two temperature dependences of the fluorine pressure above this compound in equilibrium with AgF(s) and AgF(l), log(p/kPa) = (11.39 +/- 0.30) (11060 +/- 300)(T/K) (from (655 to 706) K) and log(p/kPa) = (10.27 +/- 0.20) - (10220 +/- 200)(T/K) (from (710 to 776) K), respectively, were determined. At these temperatures, fluorine is partially decomposed so that two partial molar standard enthalpies of AgF2 associated to the sublimation reactions, AgF2(s) -> AgF(s) + F(g) and AgF2(s) -> AgF(s) + 1/2F(2)(g), Delta H-sub degrees(298 K) = (195 +/- 10) kJ.mol(-1) and (125 5) kJ.mol(-1), were calculated.