THERMODYNAMICS OF THE FORMATION OF COMPLEX-COMPOUNDS IN FUSED SALT-SOLUTIONS - K2S2O7-V2O5

Using the experimental values of the heat of mixing, the conductivity and the density of binary molten salt K2S2O7-V2O5 mixtures, this work shows that it is possible to deduce the thermodynamic parameters associated with reactions of formation of complex compounds: equilibrium constants and enthalpies. The ideal associated solution model has been used to give a thermodynamic description of the solution. The binary melt was assumed to consist of K4(VO2)2(SO4)2S2O7 (compound A), KVO2SO4 (compound B), K+, S2O7(2-) and V2O5 in equilibrium as V2O5 + 2 K2S2O7 --> K4(VO2)2(SO4)2S2O7 V2O5 + K2S2O7 --> 2 KVO2SO4 giving a quaternary solution. On the basis of the measured conductivities and densities, and under the assumption that free K+ and S2O7(2-) are carrying all the current, the equivalent conductance of the mixture can be calculated. If we assume that the quaternary solution is ideal (as regards conductance) we can calculate the two equilibrium constants. By using these results together with the experimental values for the excess molar enthalpy the heat of formation of the two complex compounds can be obtained by the least-mean-squares method.