Thermochemical studies on BaMoO 4(s)

Abstract

The standard molar Gibbs energy of formation of BaMoO 4(s) has been determined by measuring e.m.f. of the cell: Pt/BaMoO 3(s)+BaMoO 4(s))/CSZ/air ( p(O 2)=21.21 kPa)/Pt where CSZ represents 15 mol% CaO stabilized zirconia. E.m.f. measurements were carried out in the temperature range 1091 to 1309 K and its dependence on temperature could be represented by: E(V)±0.001=1.482−3.600×10 −4 T(K). Using the Gibbs energy data on BaMoO 3(s) from our previous study along with the above e.m.f. data, the Δ f G m o( T) for BaMoO 4(s) was calculated to be: Δ f G o m ( BaMoO 4, s , T)( kJ mol −1 )±4.7=−1542.0+0.3552T( K) Δ f H m o(298.15 K) is calculated by the second-law method using the relevant heat capacity data and the variation of Δ f G m o(BaMoO 4, s, T) with temperature and the value is −(1557.5±3.6) kJ mol −1. The third-law values of Δ f H m o(298.15 K) at each experimental temperature were also calculated from free enthalpy functions −{( G o( T)− H o(298.15 K))/ T} reported in the literature. The mean Δ f H m o(298.15 K) value by this method is −(1536.8±5.2) kJ mol −1.