Cesium diuranate (Cs 2U 2O 7): heat capacity (5 to 350 K) and thermodynamic functions to 350 K. A re-evaluation of the standard enthalpy of formation and the thermodynamics of (cesium + uranium + oxygen)

• Published in: The Journal of chemical thermodynamics 1981-01, Vol.13 (11), p.1075-1080
• Main Authors: O'Hare, P.A.G., Flotow, H.E., Hoekstra, H.R.
• Format: Article
• Language: English
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/0021-9614(81)90005-7

The low-temperature (5 to 350 K) heat capacity of a well-characterized sample of β-Cs 2U 2O 7 has been measured by adiabatic calorimetry. No anomalies were observed in the plot of heat capacity against temperature, the curve having the normal sigmoid shape. These measurements were used to calculate thermodynamic functions to 350 K. At T = 298.15 K, the following results were obtained: C ° = (231.23±0.46) J K −1; S °(T) = (327.75±0.66) J K −1 mol −1 {H °(T)−H °(0)} = (45544±91)J mol −1; {G °(T)−H °(0)/T =−()175.00±0.35} J K −1 mol −1 . Because of recent critical re-evaluations of thermochemical quantities for UO 2Cl 2, the published value for ΔH f o(Cs 2U 2O 7, c, β, 298.15 K) has been revised to −(3220±1.8) kJ mol −1. A discussion of the thermodynamics of (cesium + uranium + oxygen) at high temperatures is included.