Thermodynamic stability of SrThF6(cr) and BaThF6(cr)

In the present paper we report the standard molar Gibbs energy of formation of SrThF6 and BaThF6 measured by gas equilibration method employing transpiration technique. The chemical equilibrium between MThF6 (cr) (M = Sr, Ba) and moisture: MThF6(cr)+2H2O(g)=MF2(cr)+ThO2(cr)+4HF(g) has been employed to determine thermodynamic stability of these compounds. The equilibrium constant 'Kp' at different temperatures was calculated using partial pressure of HF(g) measured at a fixed vapour pressure of water p(H2O). The Gibbs energy of formation for SrThF6(cr) and BaThF6(cr) could be expressed as: ΔfG°m (SrThF6, cr)(±8 kJ mol−1) = −3288 + 0.3776 T and ΔfG°m (BaThF6, cr) (±7 kJ mol−1) = −3292 + 0.378T. The isobaric heat capacity of these compounds was measured employing differential scanning calorimetric technique. Based on the experimental results thermodynamic functions for SrThF6 and BaThF6 have been generated.