The enthalpy of formation of IrO2 and thermodynamic functions

The Gibbs energy of formation of IrO₂(s) has been measured by means of oxygen dissociation pressure measurements, and by EMF measurements using ZrO₂ (+ CaO) as the solid electrolyte. In addition, high-temperature enthalpy increments of IrO₂ have ben measured from 416 to 940 K using a drop calorimeter. A “third law” evaluation of the experimental results and data from literature has been made. For the enthalpy of formation of IrO₂(s) the value ΔH°_f (298.15 K) - −(59.60 ± 0.03) kcal mole⁻¹ has been selected. The thermodynamic functions of IrO₂(s) have been calculated in the temperature range 298–1200 K.