THERMAL-DECOMPOSITION AND SOLUTION CALORIMETRY OF AMMONIUM EUROPIUM CHLORIDES

The thermal decomposition equilibria of ammonium europium chlorides (N H4)(3)EuCl6, (NH4)(2)EuCl5 and NH4Eu2Cl7 have been investigated by tot al pressure measurements in a membrane zero manometer. The thermodynam ic data of these solid phases have been derived from the decomposition functions. The standard enthalpies of solution in 4n HCl (aq.) of (NH 4)(3)EuCl6, (NH4)(2)EuCl5, NH4Eu2Cl7, EuCl3 and Eu2O3 were measured. O n the basis of these values and tabulated data, the standard enthalpie s at 298 K of the ammonium europium chlorides were derived and compare d with the obtained results from the total pressure measurements. Data by total pressure measurement: Delta H(B)degrees((NH4)(3)EuCl6,f,298) = -448,7 +/- 5,1 kcal/mol; S degrees((NH4)(3)EuCl6,f,298) = 118,9 +/- 8,3 cal/K.mol; Delta H(B)degrees((NH4)(2)EuCl5,f,298) = -377,3 +/- 4, 5 kcal/mol; S degrees((NH4)(2)EuCl5,f,298) = 85,4 +/- 7,6 cal/K.mol De lta H(B)degrees(NH4Eu2Cl7,f,298) = -519,8 +/- 3,5 kcal/mol; S degrees( NH4Eu2Cl7,f,298) = 94,2 +/- 5,5 cal/K.mol. Data by solution calorimetr y: Delta H(B)degrees(EuCl3,f,298) = -218,3 +/- 0,8 kcal/mol; Delta H(B )degrees((NH4)(3)EuCl6,f,298) = -444,6 +/- 1,2 kcal/mol; Delta H(B)deg rees((NH4)(2)EuCl5,f,298) = -374,0 +/- 1,1 kcal/mol; Delta H(B)degrees (NH4Eu2Cl7,f,298) = -513,6 +/- 1,8 kcal/mol.