SUBLIMATION STUDY OF TELLURIUM TETRACHLORIDE AND TETRAIODIDE FROM THEIR VAPOR-PRESSURE MEASUREMENTS

The total vapour pressures of tellurium tetrachloride (TeCl4) and tetr aiodide (TeI4) were measured by torsion-effusion method, and their tem perature dependences are respectively represented by the following equ ations: log{p (kPa)} = (10.78 +/- 0.20) - (5290 +/- 100)/T (K); log{p (kPa)} = (10.33 +/- 0.40) - (4654 +/- 150)IT (K). TeCl4 sublimes congr uently, such that TeCl4(s) --> TeCl4(g), and the standard sublimation enthalpy as obtained from second- and third-law treatments of the pres sure data, -and entropy associated with this reaction, are DELTA(sub)H -degrees(298) = 105 +/- 2 kJ mol-1 and DELTA(sub)S-degrees(298) = 180 +/- 4 J K-1 mol-1. In the temperature range considered (340-396 K), Te I4(S) decomposes by the reaction 1/2TeI4(S) --> 1/2Te(s) + I2(g) and, in a minor amount, by the reaction TeI4(s) --> TeI2(g) + I2(g) The sta ndard enthalpies and entropies of both reactions were calculated from the total vapour pressure data: DELTA(r)H-degrees(298) = 87 +/- 4 kJ m ol-1 and DELTA(r)S-degrees(298) = 163 +/- 10 J K-1 mol-1 for the first reaction, and DELTA(r)H-degrees(298) = 181 +/- 4 kJ mol-1 and DELTA(r )S-degrees(298) = 303 +/- 12 J K-1 mol-1 for the second reaction. The heat of formation of TeI4(s), i.e. DELTA(for)H-degrees(298) = -50 +/- 8 kJ mol-1, was also derived.