INVESTIGATION ON THE THERMAL-DECOMPOSITIO N OF AMMONIUM HALIDES

The decomposition equilibria of Ammonium Lanthanum Halides (NH4)(2)LaX 5 were determined by total pressure measurements in a membrane zero ma nometer. The phases (NH4)(2)LaX5 decompose in one step to give solid L aX3 and gaseous NH3 and HX. From the decomposition functions the entha lpies of formation and the standard entropies of the phases are derive d. Delta H-B degrees(NH4)(2)LaCl5,f,298) = -411,7 +/- 2,2 kcal/mol; S degrees((NH4)(2)LaCl5,f,298) = 86,7 +/- 2,3 cal/Kmol; Delta H-B degree s(NH4)(2)LaBr5,f,298) = -351,6 +/- 3,5 kcal/mol; S degrees((NH4)(2)LaB r5,f,298) = 101,1 +/- 1,8 cal/Kmol; Delta H-B degrees(NH4)(2)LaI5,f,29 8) = -268,91 +/- 3,9 kcal/mol; S degrees((NH4)(2)LaI5,f,298) = 115,5 /- 4,3 cal/Kmol.