Thermal decomposition and solution calorimetry of ammonium neodymium bromides

The thermal decomposition equilibria of ammonium neodymium bromides (NH4)(3)NdBr6, (NH4)(2)NdBr5 and NH4Nd2Br7 have been investigated by total pressure measurements. The thermodynamical data of these solid phase complexes have been derived from the decomposition functions. The standard enthalpies of solution in 4N HBr (aq.) of (NH4)(3)NdBr6, (NH4)(2)NdBr5, NH4Nd2Br7, NdBr3 and Nd2O3 were measured. On the basis of these values and tabulated data, the standard enthalpies at 298 K of the ammonium neodymium bromides were derived and compared with the results obtained from the total pressure measurements. Data by total pressure measurement: Delta H(B)degrees((NH4)(3)NdBr6,f,298) = -399,1 +/- 4,9 kcal/mol; S degrees((NH4)(3)NdBr6,f,298) = 153,4 +/- 7,4 cal/K.mol; Delta H(B)degrees((NH4)(2)NdBr5,f,298) = -343,0 +/- 4,4 kcal/mol; S degrees((NH4)(2)NdBr5,f,298) = 109,9 +/- 6,8 cal/K.mol; Delta H(B)degrees(NH4Nd2Br7,f,298) = -484,0 +/- 5,1 kcal/mol; S degrees(NH4Nd2Br7,f,298) = 127,9 +/- 6,6 cal/K.mol. Data by solution calorimetry: Delta H(B)degrees(NdBr3,f,298) = -208,7 +/- 1,6 kcal/mol; Delta H(B)degrees((NH4)(3)-NdBr6,f,298) = -404,8 +/- 2,7 kcal/mol; Delta H(B)degrees((NH4)(2)NdBr5,f,298) = -344,2 +/- 2,4 kcal/mol; Delta H(B)degrees(NH4Nd2Br7,f,298) = -482,7 +/- 3,7 kcal/mol.