AN ELECTROCHEMICAL INVESTIGATION OF THE THERMODYNAMIC PROPERTIES OF NA2MO2O7 AND NA2NIO2

The thermodynamic properties of the compounds Na2Mo2O7 and Na2NiO2 wer e determined by using the high temperature galvanic cells Pt,Ar + CO2 + O-2, Na2CO3 \NASICON\Na2Mo2O7 + Na2MoO4, O-2 + CO2 + Ar,Pt (I) and P t,Ar, Ni + NiO + Na2NiO2 \NASICON\Na2Mo2O7 + Na2MoO4 + MoO2, Ar,Pt (II ) in the temperature range 650-800 K and 673-773 K, respectively. The reversible emf of cell-I, at P-CO2 = 112.6 and 282 Pa, and cell-II can be expressed as E'(1)(P-CO2 = 112.6 Pa) = -282.7 + 1.13T (+/- 2) mV, E''(1)(P-CO2 = 282 Pa) = -274.7 + 1.081T (+/- 2) mV and E-II = 1383 0.230T (+/- 1.5) mV, respectively. The standard Gibbs energy of format ion of Na2Mo2O7 and Na2NiO2 from elements computed from the emf's of t he cells and auxiliary information from the literature are expressed a s Delta(f)G(m) degrees<Na2Mo2O7) = -2240.0 + 0.618T (+/- 2) kJ mol(-1) and Delta(f)G(m) degrees<Na2NiO2) = -684.1 + 0.257T. (+/- 7) kJ mol(- 1) respectively. (C) 1997 Elsevier Science B.V.