Vapor Pressures and Sublimation Enthalpies of Cadmium Difluoride and Zinc Difluoride by the Torsion-Effusion Method

The vapor pressures over solid CdF(2) and ZnF(2) were measured by the torsion-effusion method. The temperature dependencies of the vapor pressures of these compounds were found to fit the following equations: log(p/ kPa) = (9.55 +/- 0.30) - (13920 +/- 300)(T/K) (from (962 to 1149) K), and log(p/kPa) = (9.79 +/- 0.40) - (12510 +/- 400)(T/K) (from (846 to 1047) K) for CdF(2) and ZnF(2), respectively. Treating these vapor pressures by the second- and third-law methods, the standard sublimation enthalpies Delta(sub)H degrees(298 K) = (285 +/- 10) kJ.mol(-1) and (257 +/- 8) kJ.mol(-1) and entropies Delta(sub)S degrees(298 K) = (163 +/- 6) J.K(-1) mol(-1) and (169 +/- 8) J.K(-1).mol(-1) for CdF(2) and ZnF(2), respectively, were calculated.