Heat capacity and Gibbs energy of formation of the ternary oxide CdRh 2O 4(s)

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The standard molar Gibbs free energy of formation of CdRh 2O 4(s) was determined using an oxide solid-state electrochemical cell wherein calcia-stabilized-zirconia (CSZ) was used as an electrolyte. The oxide cell can be represented by: ( − ) Pt − Rh / { CdO ( s ) + CdRh 2 O 4 ( s ) + Rh(s) } / / CSZ// O 2 ( p ( O 2 ) = 21.21 kPa ) / Pt−Rh(+) The electromotive force was measured in the temperature from 855.5 K to 1144.9 K. The standard molar Gibbs energy of formation of CdRh 2O 4(s) from elements in their standard state using the oxide electrochemical cell has been calculated and can be represented by: Δ f G 0 { CdRh 2 O 4 ( s ) } / kJ ⋅ mol − 1 ( ± 1.13 ) = − 712.44 + 0.395 T ( K ) . Standard molar heat capacity C o p,m( T) of CdRh 2O 4(s), was measured using a heat flux type differential scanning calorimeter (DSC) in two different temperature ranges, from 127 K to 299 K and 307 K to 845 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: C p , m 0 ( CdRh 2 O 4 , s , T ) ( J · K − 1 · mol − 1 ) = 178.65 + 2.943 ⋅ 10 − 2 T ( K ) − 32.52285 ⋅ 10 5 / T 2 ( K ) . The heat capacity of CdRh 2O 4(s), was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound from elements at 298.15 K.