Cesium uranate, Cs2UO4: heat capacity and entropy from 5 to 350 K and standard Gibbs energy of formation at 298.15 K

Abstract The heat capacity of a sample of very pure Cs 2 UO 4 was determined from 5 to 350 K by adiabatic calorimetry. No unusual thermal behaviour was observed. The following thermodynamic results for Cs 2 UO 4 were obtained: heat capacity at constant pressure: C p o (298.15 K) = (152.76±0.31) J K −1 mol −1 ; entropy: S o (298.15 K) = (219.66±0.44) J K −1 mol −1 ; { H o (298.15 K) − H o (0)} = (30815±62) J mol −1 ; { G o (298.15 K) − H o (0)}/298.15 K = −(116.31±0.23) J K −1 mol −1 . The enthalpy of formation of Cs 2 UO 4 recently reported by O'Hare and Hoekstra and the entropies of Cs 2 UO 4 , Cs, U, and O 2 were used to calculate the standard Gibbs energy of formation: ΔG f o (Cs 2 UO 4 , c, 298.15 K) = −(1774.8±3.6) kJ mol −1 .