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Title: Low temperature heat capacities and standard molar enthalpy of formation of the coordination compound Zn(His)(NO<sub>3</sub>)<sub>2</sub>.1/2H<sub>2</sub>O(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
Amino acids
Isoperibol solution-reaction calorimetry
Issue Date: Mar-2010
Publisher: CSIR
Abstract: Low temperature heat capacities of the solid coordination compound Zn(His)(NO<sub>3</sub>)<sub>2</sub>.1/2H<sub>2</sub>O(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, <i style="">T</i><sub>D </sub>= 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 (<i style="">X</i>), [<i style="">X</i> = <i style="">f </i>(<i style="">T</i>)], by least squares method. Enthalpies of dissolution of {ZnSO<sub>4</sub>.7H<sub>2</sub>O(s) + 2NaNO<sub>3</sub>(s) + L-His(s)} and {Zn(His)(NO<sub>3</sub>)<sub>2</sub>.1/2H<sub>2</sub>O(s) + Na<sub>2</sub>SO<sub>4</sub>(s)} in 100 ml of 2 mol dm<sup>-3</sup> HCl(aq) at <i style="">T</i> = 298.15 K have been determined to be <i style=""></i>Δ<sub>d</sub><i>H</i><sup>0</sup><sub>m,1</sub>= 79.830 ± 0.058 kJ mol<sup>-1</sup> and <i style=""></i>Δ<sub>d</sub><i>H</i><sup>0</sup><sub>m,2</sub>= 51.146 ± 0.041 kJmol<sup>-1</sup> respectively, with a isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound is determined as <b style=""></b>Δ<sub>f</sub><i>H</i><sup>0</sup><sub>m</sub>(Zn(His)(NO<sub>3</sub>)<sub>2</sub>.1/2H<sub>2</sub>O, s, 298.15 K) = - 1207.19 ± 2.82 kJ mol<sup>-1</sup> 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 {ZnSO<sub>4</sub>.7H<sub>2</sub>O(<sub>S</sub>) + 2NaNO<sub>3</sub>(s) + L-His(s)} and from dissolution of the {Zn(His)(NO<sub>3</sub>)<sub>2</sub>.1/2H<sub>2</sub>O(s) + Na<sub>2</sub>SO<sub>4</sub>(s)} mixtures.
Description: 295-301
Appears in Collections:IJC-A Vol.49A(03) [March 2010]

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