Standard Molar Gibbs Energy of Formation of Ba3Te2O9(s) by Transpiration Technique.

Abstract

Abstract The standard molar Gibbs energy of formation of barium tellurite, Ba 3 Te 2 O 9 (s), was determined by the transpiration technique using pure oxygen as the carrier gas in the temperature range from 1119 to 1280 K. The condensate was exclusively identified as TeO 2 (s) by chemical analysis. Chemical analysis of the residue left in the alumina boat after the transpiration experiments confirmed the coexistence of BaO(s) with Ba 3 Te 2 O 9 (s) during the vaporization reaction. The incongruent vaporization reaction could be established as: Ba 3 Te 2 O 9 (s)=3BaO(s)+2TeO 2 (g)+O 2 (g). From the quantitative chemical analysis of the condensed TeO 2 (s), the vapor pressure of TeO 2 (g) over pure Ba 3 Te 2 O 9 (s) was calculated. The equilibrium constant for the incongruent vaporization reaction at each temperature has been calculated from the vapor pressure data and is fitted to an expression: ln K (±1.0)=11.32–55518.6·( K /T) . The Gibbs energy of formation of Ba 3 Te 2 O 9 (s) was computed from the above data and the values of Δ f G° m for BaO(s) and TeO 2 (g) taken from the literature and are given by: {Δ f G ° m (Ba 3 Te 2 O 9 , s, T )±3.0}/(kJ mol −1 )=−2296.8+0.4302·( T /K).