Measurement of the Standard Free Energy of Formation of Sulfides and Sulfates Using Oxygen Concentration Cells with ZrO2·CaO

The following cells were constructed with ZrO2·CaO as an electrolyte and pure SO2 gas was supplied to the tesing electrode chamber. pure SO2, MnO, MnS, Pt/ZrO2·CaO/Pt, Air… (1) pure SO2, Cu, Cu2S, Pt/ZrO2·CaO/Pt, Air… (2) pure SO2, NiO, NiSO2, Pt/ZrO2·CaO/Pt, Air… (3) pure SO2, CoO, CoSO2, Pt/ZrO2·CaO/Pt, Air… (4) pure SO2, Fe2O2, Fe2 (SO2) 2, Pt/ZrO2·CaO/Pt, Air… (5) The electromotive forces of those cells in the temperature range from 800 to 1400K were generally very stable and very reproducible except for the cell of equation (3). Reversibility of the electromotive forces was proved sufficiently good by supplying a small external current to the cells. From the electromotive forces and the standard free energies of formation of the relevant oxides, those of MnS, Cu2S, NiSO4, CoSO4 and Fe2 (SO4) 3 were determined as follows. The above free energy changes showed good agreements with the previous data by other investigators except for iron sulfate. However, all of the standard deviations of the present data were much smaller than those of the data by other investigators.