The standard enthalpy and entropy of formation of Rh2O3 - A third-law optimization

The standard Gibbs energy of formation of Rh2O3 at high temperature has bee n determined recently with high precision. The new data are significantly d ifferent from those given in thermodynamic compilations. Accurate values fo r enthalpy and entropy of formation at 298.15 K could not be evaluated from the new data, because reliable values for heat capacity of Rh2O3 were not available. In this article, a new measurement of the high temperature heat capacity of Rh2O3 using differential scanning calorimetry (DSC) is presente d. The new values for heat capacity also differ significantly from those gi ven in compilations. The information on heat capacity is coupled with stand ard Gibbs energy of formation to evaluate values for standard enthalpy and entropy of formation at 289.15 K using a multivariate analysis. The results suggest a major revision in thermodynamic data for Rh2O3 For example, it i s recommended that the standard entropy of Rh2O3 at 298.15 K be changed fro m 106.27 J mol(-1) K-1 given in the compilations of Barin and Knacke ct al. to 75.69 J mol(-1) K-1. The recommended revision in the standard enthalpy of formation is from -355.64 kJ mol(-1) to -405.53 kJ mol(-1).