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Refinement of the Thermodynamic Properties of Ruthenium Dioxide and Osmium Dioxide
Author(s) -
Jacob K. Thomas,
Mishra Saurabh,
Waseda Yoshio
Publication year - 2000
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2000.tb01459.x
Subject(s) - gibbs free energy , chemistry , enthalpy , heat capacity , electrolyte , atmospheric temperature range , electrode , analytical chemistry (journal) , standard molar entropy , standard electrode potential , standard enthalpy of formation , calorimetry , thermodynamics , electrochemistry , electrode potential , physics , chromatography
The standard Gibbs energies of formation of RuO 2 and OsO 2 at high temperature have been determined with high precision, using a novel apparatus that incorporates a buffer electrode between the reference and working electrodes. The buffer electrode absorbs the electrochemical flux of oxygen through the solid electrolyte from the electrode with higher oxygen chemical potential to the electrode with lower oxygen potential. The buffer electrode prevents polarization of the measuring electrode and ensures accurate data. The standard Gibbs energies of formation (Δ f G °) of RuO 2 , in the temperature range of 900–1500 K, and OsO 2 , in the range of 900–1200 K, can be represented by the equationswhere the temperature T is given in Kelvin and the deviation of the measurement is ±80 J/mol. The high‐temperature heat capacities of RuO 2 and OsO 2 are measured using differential scanning calorimetry. The information for both the low‐ and high‐temperature heat capacity of RuO 2 is coupled with the Δ f G ° data obtained in this study to evaluate the standard enthalpy of formation of RuO 2 at 298.15 K (Δ f H ° 298.15K ). The low‐temperature heat capacity of OsO 2 has not been measured; therefore, the standard enthalpy and entropy of formation of OsO 2 at 298.15 K (Δ f H ° 298.15K and S° 298.15K , respectively) are derived simultaneously through an optimization procedure from the high‐temperature heat capacity and the Gibbs energy of formation. Both Δ f H ° 298.15K and S ° 298.15K are treated as variables in the optimization routine. For RuO 2 , the standard enthalpy of formation at 298.15 K is Δ f H ° 298.15K (RuO 2 ) =−313.52 ± 0.08 kJ/mol, and that for OsO 2 is Δ f H ° 298.15K (OsO 2 ) =−295.96 ± 0.08 kJ/mol. The standard entropy of OsO 2 at 298.15 K that has been obtained from the optimization is given as S ° 298.15K (OsO 2 ) = 49.8 ± 0.2 J·(mol·K) −1 .