Heat capacity and thermodynamics of solid and liquid pyridine-3-carboxylic acid (nicotinic acid) over the temperature range 296K to 531K
2012; Elsevier BV; Volume: 55; Linguagem: Inglês
10.1016/j.jct.2012.06.010
ISSN1096-3626
AutoresAbhinav Joseph, Carlos E. S. Bernardes, Manuel E. Minas da Piedade,
Tópico(s)Thermodynamic properties of mixtures
ResumoThe molar heat capacity of pyridine-3-carboxylic acid (nicotinic acid) for T = (296 to 531) K was investigated by differential scanning calorimetry (DSC) and Calvet-drop microcalorimetry. The measurements extended up to the liquid range and also covered the interval where a reversible and fast solid-solid (cr II → cr I) phase transition occurs. The molar enthalpies and entropies of that phase transition and of fusion were obtained as Ttrs = (455.0 ± 0.2) K, ΔtrsHmo = (0.90 ± 0.10) kJ ⋅ mol−1, ΔtrsSmo = (1.98 ± 0.22) J ⋅ K−1 ⋅ mol−1, Tfus = (509.91 ± 0.04) K, ΔfusHmo = (28.2 ± 0.1) kJ ⋅ mol−1, and ΔfusSmo = (55.30 ± 0.16) J ⋅ K−1 ⋅ mol−1. By combining these experimental results with the previously reported ΔsubHm(NA,cr II) at T = 366.5 K, the corresponding entropy in the gaseous state calculated at the B3LYP/6-31+G(d,p) level of theory, and ΔfHmo(NA),cr II) at T = 298.15 K, it was possible to estimate the standard molar Gibbs energy of formation functions necessary for the construction of the ΔfGm∘ vs. T diagram illustrating the enantiotropic nature of this system.
Referência(s)