Sublimation study of tellurium tetrachloride and tetraiodide from their vapour pressure measurements

Abstract

The total vapour pressures of tellurium tetrachloride (TeCl 4) and tetraiodide (TeI 4) were measured by torsion-effusion method, and their temperature dependences are respectively represented by the following equations: log{ p (kPa)} = (10.78 ± 0.20) − (5290 ± 100)/ T (K); log{ p (kPa) = (10.33 ± 0.40) − (4654 ± 150)/ T (K). TeCl 4 sublimes congruently, such that TeCl 4(s) → TeCl 4(g), and the standard sublimation enthalpy as obtained from second- and third-law treatments of the pressure data, and entropy associated with this reaction, are Δ sub H o(298) = 105 ± 2 kJ mol −1 and Δ sub S o(298) = 1804 ± 4 J K −1 mol −1. In the temperature range considered (340–396 K), TeI 4(s) decomposes by the reaction 1 2 Te I 4(s)→ 1 2 Te(s)+ I 2(g) and, in a minor amount, by the reaction Te I 4(s)→Te I 2(g)+I 2(g) The standard enthalpies and entropies of both reactions were calculated from the total vapour pressure data: Δ r H o(298) = 87 ± 4 kJ mol −1 and Δ r S o(298) = 163 ± 10 J K −1 mol −1 for the first reaction, and Δ r H o(298) = 181 ± 4 kJ mol −1 and Δ r S o(298) = 303 ± 12 J K −1 mol −1 for the second reaction. The heat of formation of TeI 4(s), i.e. Δ for H o(298) = −50 ± 8 kJ mol −1, was also derived.