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

Abstract

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 A sub H°(298 K) = (285 ± 10) kJ·mol -1 and (257 ± 8) kJ·mol -1 and entropies A sub S°(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.