Vapor Pressure and Sublimation Enthalpies of Mercury(I,II) Fluorides by the Torsion Effusion Method

The vapor pressures in equil. over HgF2 and Hg2F2 were measured by the torsion-effusion method. HgF2 vaporized congruently. The temp. dependence of the vapor pressure of this compd. was found to fit the following equation: HgF2(s), log(p/kPa) = (9.00 ± 0.30) to (6750 ± 200)(K/T) (from (496 to 629) K). Treating the vapor pressure data by the second- and third-law methods, the std. sublimation enthalpy, ΔsubH°(298 K) = (136 ± 4) kJ/mol-1, and entropy, ΔsubS°(298 K) = (145 ± 6) J/K-1/mol-1, were selected. In the covered temp. range (from (457 to 589) K), Hg2F2(s) decomps. into HgF2(s) and Hg(g) so that the temp. dependence of the mercury pressure above this compd., log(p/kPa) = (7.90 ± 0.50) to (5400 ± 300)(K/T), was detd. Also, for this compd., the std. sublimation enthalpy, ΔsubH°(298 K) = (105 ± 4) kJ/mol-1, and entropy, ΔsubS°(298 K) = (114 ± 10) J/K-1/mol-1, were detd.