A CRITICAL-ASSESSMENT OF THE STANDARD MOLAR GIBBS FREE-ENERGY OF FORMATION OF NIWO4

Three independent studies have been reported on the free energy of formation of NiWO4. Results of these measurements are analyzed by the ''third-law'' method, using thermal functions for NiWO4 derived from both low and high temperature heat capacity measurements. Values for the standard molar enthalpy of formation of NiWO4 at 298.15 K obtained from ''third-law'' analysis are compared with direct calorimetric determinations. Only one set of free energy measurements is found to be compatible with calorimetric enthalpies of formation. The selected value for Delta(f) H-m(0)(NiWO4,cr, 298.15 K) is the average of the three calorimetric measurements, using both high temperature solution and combustion techniques, and the compatible free energy determination. A new set of evaluated data for NiWO4 is presented.