Thermodynamic characterization of lanthanum tellurate

Abstract

Abstract The standard Gibbs energy of formation of lanthanum tellurate, La 2 TeO 6 was derived from its vapour pressure measurements in the temperature range 1420–1520 K employing TG based transpiration method. The temperature dependence of vapour pressure of TeO 2 vapour over the mixture La 2 TeO 6 (s) + La 2 O 3 (s) generated by the incongruent vapourisation reaction, La 2 TeO 6 ( s ) → La 2 o 3 ( s ) + TeO 2 ( g ) + 1 / 2 O 2 ( g ) could be represented as: log p (Pa) = [18.47−27127/ T (K)] ± 0.03 (1420–1520 K). Enthalpy increments on La 2 TeO 6 were determined by using inverse drop calorimetry in the temperature range 583–1287 K and the thermodynamic functions, namely, heat capacity, entropy and Gibbs energy functions were derived. The mean value of −2381.3 ± 2.0 kJ mol −1 was obtained for Δ f H 298 ∘ (La 2 TeO 6 ) by combining the value of Δ f G ∘ (La 2 TeO 6 ) derived from vapour pressure data and the free energy functions of La 2 TeO 6 derived from the drop calorimetry data.