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The thermal decomposition and thermodynamic properties of uranium pentabromide

Authors
Journal
Journal of Inorganic and Nuclear Chemistry
0022-1902
Publisher
Elsevier
Publication Date
Volume
35
Issue
11
Identifiers
DOI: 10.1016/0022-1902(73)80071-5

Abstract

Abstract The thermal decomposition of uranium pentabromide has been studied; and the free energy and standard heat of formation of this compound have been measured. The standard heat of formation of UBr 5 was found to be ΔH 298 f = −197·5 ± 1·3 kcal/mole. Only at temperatures below 80°C was an apparent equilibrium established, whereby a constant bromine vapour pressure could be measured: at higher temperatures, the compound decomposes irreversibly into uranium tetrabromide and liquid bromine. At 80°C the free energy of UBr 5 from UBr 4 and bromine vapour is ΔG = -0·3 kcal/mole, and by extrapolation would be zero at about 100°C. The cause of the irreversible decomposition above 80°C is not known, but it may be associated with a change in crystal structure.

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