Low-Temperature Heat Capacities and Standard Molar Enthalpy of Formation of Chromium Nicotinate Cr(C6H4NO2)3(s)

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• 作者：You-Ying Di ; Wei-Wei Yang ; Yu-Xia Kong ; Quan Shi ; Zhi-Cheng Tan
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2008
• 出版时间：January 2008
• 年：2008
• 卷：53
• 期：1
• 页码：94 - 99
• 全文大小：97K
• 年卷期：v.53,no.1(January 2008)
• ISSN：1520-5134

文摘

Low-temperature heat capacities of the solid coordination compound Cr(C₆H₄NO₂)₃(s) have been measured by a precision automated adiabatic calorimeter over the temperature range T = 78 K to T = 391 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C_p,m) with the reduced temperatures (X), [X = f(T)], by a least-squares method. The smoothed molar heat capacities and thermodynamic functions of the complex Cr(C₆H₄NO₂)₃(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K are tabulated with an interval of 5 K. Enthalpies of dissolution of {3C₆H₅NO₂(s)} [Δ_dH_m^{GNU Unifont">⊖}(1)] and Cr(C₆H₄NO₂)₃(s) [Δ_dH_m^⊖(3)] in 100.00 mL of 0.1 mol·dm⁻³ HCl and {Cr(OH)₃(s)} [Δ_dH_m^⊖(2)] in 100.00 mL of 0.1 mol·dm⁻³ HCl solution containing certain amounts of nicotinic acid (named as solution A₁) at T = 298.15 K were, respectively, determined to be [(14.44 ± 0.14), −(34.47 ± 0.26), and −(25.74 ± 0.13)] kJ·mol⁻¹ by means of an isoperibol solution reaction calorimeter. The enthalpy change Δ_rH_m(5) of the designed solid-state coordination reaction of Cr(OH)₃(s) with nicotinic acid can be calculated as Δ_rH_m(5) = (52.04 ± 0.52) kJ·mol⁻¹ in accordance with a thermochemical cycle and the experimental results. The standard molar enthalpy of formation of the compound was determined as Δ_fH_m^⊖[Cr(C₆H₄NO₂)₃, s, 298.15 K] = −(1189.6 ± 2.8) kJ·mol⁻¹, from the enthalpies of dissolution and other auxiliary thermodynamic data.