High-temperature calorimetric studies on the thermal properties of Rb 2U(SO 4) 3(s)

Abstract

Measurements of the enthalpy increment, ( H ⊖ T − H ⊖ 298.15) for Rb 2U(SO 4) 3 were carried out in the range 370–800 K using a high-temperature Calvet calorimeter. Solid state transitions were observed at 625 ± 3K and 763 ± 2K, with respective enthalpies of transitions of 5.998 and 13.585 kJ mol −1. The H ⊖ T - H ⊖ 298.15 values were plotted against temperature and can be given in J mol −1 by H ⊖ T − H ⊖ 2987.15± 694/(J mol −1) = −1.117 × 10 5+368.9 T/K + 0.0199 T 2/ K 2 (from 370 to 628K); H ⊖ T - H ⊖ 298.15 ±405/(Jmol −1) = 3.279 × 10 3 + 13.4 T/K + 0.3063 T 2/K 2 (from 630 to 760 K); and H ⊖ T − H ⊖ 298.15 ± 433/(J mol −1) = −6.671 × 10 5 + 1140 T/K (from 765 to 803K). The thermodynamic properties of Rb 2U(SO 4) 3(s) were derived using the estimated value of H ⊖ 298.15.