Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Low-temperature heat capacities of the solid coordination compound Zn(Leu)SO4*1/2H2O(s) were measured by a precision automated adiabatic calorimeter over the temperature range between T = 78 K and T = 371 K. The initial dehydration temperature of the coordination compound was determined to be TD = 326.50 K by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities (Cp,m) with the reduced temperatures (x), [x = f (T)], by least-squares method. Enthalpies of dissolution of the [ZnSO4*7H2O(s) + Leu(s)] () and the Zn(Leu)SO4*1/2H2O(s) () in 100.00 mL of 2 mol*dm-3 HCl(aq) at T = 298.15 K were determined to be = -(85.80 +- 0.09) kJ*mol-1 and = (55.97 +- 0.06) kJ*mol-1 by means of a homemade isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as (Zn(Leu)SO4*1/2H2O, s, 298.15 K) = -(1999.0 +- 0.9) kJ*mol-1 from the enthalpies of dissolution and other auxiliary thermodynamic data through a Hess thermochemical cycle. Furthermore, the reliability of the Hess thermochemical cycle was verified by comparing UV/Vis spectra and the refractive indexes of solution A (from dissolution of the [ZnSO4*7H2O(s) + Leu(s)] mixture in 2 mol*dm-3 hydrochloric acid) and solution A' (from dissolution of the complex Zn(Leu)SO4*1/2H2O(s) in 2 mol*dm-3 hydrochloric acid).