Abstract
Low-temperature heat capacities of a solid complex Zn(Val)SO4·H2O(s) were measured by a precision automated adiabatic calorimeter over the temperature range between 78 and 373 K. The initial dehydration temperature of the coordination compound was determined to be, T D=327.05 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities (C p,m) with the reduced temperatures (x), [x=f (T)], by least square method. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were given with the interval of 5 K.
Enthalpies of dissolution of the [ZnSO4·7H2O(s)+Val(s)] (Δsol H m,l 0) and the Zn(Val)SO4·H2O(s) (Δsol H m,2 0) in 100.00 mL of 2 mol dm–3 HCl(aq) at T=298.15 K were determined to be, Δsol H m,l 0=(94.588±0.025) kJ mol–1 and Δsol H m,2 0=–(46.118±0.055) kJ mol–1, by means of a homemade isoperibol solution–reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as: Δf H m 0 (Zn(Val)SO4·H2O(s), 298.15 K)=–(1850.97±1.92) 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)+Val(s)] mixture in 2 mol dm–3 hydrochloric acid) and solution A’ (from dissolution of the complex Zn(Val)SO4·H2O(s) in 2 mol dm–3 hydrochloric acid).
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Di, Y.Y., Tan, Z.C., Li, L.W. et al. Low-temperature heat capacities and standard molar enthalpy of formation of the complex. J Therm Anal Calorim 87, 545–551 (2007). https://doi.org/10.1007/s10973-005-7431-z
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DOI: https://doi.org/10.1007/s10973-005-7431-z