Formation enthalpies and thermodynamics of some reactions of the Bi12.5R1.5ReO24.5 (R=Y, Nd, La) compounds

Solution calorimetry, using 2.0 M HCl (T=298.15 K) as a solvent, is used to study the thermochemistry of Bi12.5R1.5ReO24.5 (R=Nd, La, Y). For the first time, the standard formation enthalpies of these phases have been determined as follows: Delta H-f degrees (Bi12.5La1.5ReO24.5, s, 298.15 K)= -5659.7 +/- 8.8 kJ/mol: Delta H-f degrees (Bi12.5Nd1.5ReO24.5, s, 298.15 K)= -5702.6 +/- 9.01kJ/mol; Delta H-f degrees (Bi12.5Y1.5ReO24.5, s, 298.15 K)= -5727.6 +/- 8.8 kJ/mol. The thermodynamic stability at room temperature has been assessed. The results show that investigated phases are thermodynamically stable with respect to binary oxides and stable with respect to interaction with H2O at ambient temperatures. Bi12.5Nd1.5ReO24.5 and Bi12.5Y1.5ReO24.5 are thermodynamically stable but Bi12.5La1.5ReO24.5 is thermodynamically unstable with respect to interaction with CO2. (c) 2010 Elsevier B.V. All rights reserved.