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 for mation of NiWO4. Results of these measurements are analyzed by the ''t hird-law'' method, using thermal functions for NiWO4 derived from both low and high temperature heat capacity measurements. Values for the s tandard molar enthalpy of formation of NiWO4 at 298.15 K obtained from ''third-law'' analysis are compared with direct calorimetric determin ations. Only one set of free energy measurements is found to be compat ible 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 calor imetric measurements, using both high temperature solution and combust ion techniques, and the compatible free energy determination. A new se t of evaluated data for NiWO4 is presented.