Measurements of standard molar Gibbs energies of formation of CoGa 2O 4 and NiGa 2O 4 by the e.m.f. method

Abstract

E.m.f. measurements of the following galvanic cells with the solid electrolyte (ZrO 2 + CaO) were carried out to determine the standard molar Gibbs energies of formation of CoGa 2O 4 and NiGa 2O 4. Pt| Re| Co, CoGa 2 O 4, Ga 2 O 3|( ZrO 2 + CaO)| CoO, Co| Pt Pt| Re| Co, CoGa 2 O 4, Ga 2 O 3( ZrO 2 + CaO)| air| Pt, Pt| Re| Ni, NiGa 2 O 4, Ga 2 O 3|( ZrO 2 + CaO)| air| Pt. The values may be represented by CoO(s) + Ga 2O 3(s) = CoGa 2O 4(s); ΔG o / kJ mol −1 ± 0.12 = −22.47 − 4.999 × 10 −3 ( T K ) , ( T K = 1207 to 1379 ), 2 Co(s) + 2Ga 2O 3(s) + O 2(g) = 2CoGa 2O 4(s); ΔG o /kJ mol −1 ± 1.1 = −516.0 + 132.8 × 10 −3( T K ) , ( T K = 1057 to 1385 ), 2Ni(s) + 2Ga 2O 3(s) + O 2(g) = 2NiGa 2O 4(s); ΔG o / kJ mol −1 ± 1.3 = −524.1 + 165.6 × 10 −3( T K ) , ( T K = 1075 to 1374 ).