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IJC-A Vol.49A(03) [March 2010] >


Title: Low temperature heat capacities and standard molar enthalpy of formation of the coordination compound Zn(His)(NO3)2.1/2H2O(s) (His = L-⍺- Histidine)
Authors: Yang, Wei-Wei
Di, You-Ying
Kong, Yu-Xia
Tan, Zhi-Cheng
Gao, Sheng-Li
Keywords: Adiabatic calorimetry
Heat capacity
Standard molar enthalpy of formation
Zinc
Amino acids
Isoperibol solution-reaction calorimetry
Issue Date: Mar-2010
Publisher: CSIR
Abstract: Low temperature heat capacities of the solid coordination compound Zn(His)(NO3)2.1/2H2O(s) have been measured by a precision automated adiabatic calorimeter over the temperature range 78 - 371 K. The initial dehydration temperature of the coordination compound is determined to be, TD = 326.75 K, by analysis of the heat-capacity curve. The experimental values of the molar heat capacities in the temperature region have been fitted to a polynomial equation of heat capacities with the reduced temperature (X), [X = f (T)], by least squares method. Enthalpies of dissolution of {ZnSO4.7H2O(s) + 2NaNO3(s) + L-His(s)} and {Zn(His)(NO3)2.1/2H2O(s) + Na2SO4(s)} in 100 ml of 2 mol dm-3 HCl(aq) at T = 298.15 K have been determined to be ΔdH0m,1= 79.830 ± 0.058 kJ mol-1 and ΔdH0m,2= 51.146 ± 0.041 kJmol-1 respectively, with a isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound is determined as ΔfH0m(Zn(His)(NO3)2.1/2H2O, s, 298.15 K) = - 1207.19 ± 2.82 kJ mol-1 from the enthalpies of dissolution of the reactants and products and other thermodynamic data by a Hess thermochemical cycle. Furthermore, the reliability of the Hess thermochemical cycle has been verified by comparing UV/vis spectra and the refractive indices of solutions obtained from dissolution of the {ZnSO4.7H2O(S) + 2NaNO3(s) + L-His(s)} and from dissolution of the {Zn(His)(NO3)2.1/2H2O(s) + Na2SO4(s)} mixtures.
Page(s): 295-301
Source:IJC-A Vol.49A(03) [March 2010]

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