Standard molar Gibbs energy of formation of Ba 3Te 2O 9(s) by transpiration technique

Abstract

The standard molar Gibbs energy of formation of barium tellurite, Ba 3Te 2O 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 3Te 2O 9(s) during the vaporization reaction. The incongruent vaporization reaction could be established as: Ba 3Te 2O 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 3Te 2O 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 3Te 2O 9(s) was computed from the above data and the values of Δ fG° m for BaO(s) and TeO 2(g) taken from the literature and are given by: {Δ f G° m (Ba 3Te 2O 9, s, T)±3.0}/(kJ mol −1)=−2296.8+0.4302·( T/K).