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

ABSTRACT

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 (Cp,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)} [AdHm Q (1)] and Cr(C6H4NO2)3(s) [AdHm Q(3)] in 100.00 mL of 0.1 mol *dm-3 HCl and {Cr(OH)3(s)} [AdHm Q(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 ArHm(5) of the designed solid-state coordination reaction of Cr(OH)3(s) with nicotinic acid can be calculated as ArHm(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 AfHm Q [Cr(C6H4NO2)3, s, 298.15 K] ) -(1189.6 ( 2.8) kJ * mol-1, from the enthalpies of dissolution and other auxiliary thermodynamic data.