Thermodynamics of the sublimation of thallium(I) fluoride by simultaneous Knudsen-effusion and torsion-effusion

Abstract

The partial vapor pressures of monomeric and dimeric molecules in equilibrium with solid thallium(I) fluoride were measured by simultaneous Knudsen-effusion and torsion-effusion in the temperature range 516 to 572 K. The partial pressures of TlF(g) and Tl 2F 2(g) are expressed by: ln( p m p o ) = A − B( K T ) . The values of A and B are given. The calculated partial pressures established that the dimer constitutes 43 moles per cent of the equilibrium vapor. The third-law values of the standard molar enthalpies of sublimation Δ sub H m o(298.15 K) are (139.9±5.0) and (148.8±5.0) kJ·mol −1 for TlF(g) and Tl 2F 2(g), respectively. The third-law standard molar enthalpy change for the dissociation: Tl 2F 2(g) = 2TlF(g) is Δ r H m o(298.15 K) = (131±5) kJ·mol −1.