Аннотации:
Experimental determination of the phase transition enthalpies temperature dependences requires measurement of the transition enthalpies or the heat capacities of the final and initial states in the temperature range of interest. Both experiments are complicated and not always possible. Almost 30 years ago Chickos et al. proposed a scheme for adjustment of the sublimation, vaporization, fusion enthalpies of organic compounds to 298.15 K using readily available parameters – the heat capacities of the liquid and solid at 298.15 K, which could be calculated from the molecular structure. Since then, this scheme has been employed by most researchers in the field of thermodynamics of organic compounds and substantially facilitated the critical evaluation and comparative analysis of the phase transition enthalpies measured at different temperatures. Recently we employed solution calorimetry for the study of the sublimation, vaporization and fusion enthalpies at 298.15 K. In most cases the phase transition enthalpies adjusted to 298.15 K using Chickos et al. scheme were in agreement with the results obtained by solution calorimetry, but in some cases significant discrepancies were observed. Particularly, the fusion enthalpies of polyaromatic hydrocarbons at 298.15 K obtained using Chickos et al. scheme appeared to be systematically lower than determined by solution calorimetry, up to 10 kJ·mol−1. In the present work we analyzed the limitations of Chickos et al. scheme that could lead to the disagreement and proposed an alternative approach for adjustment of the fusion enthalpies of polyaromatic hydrocarbons to 298.15 K. During construction of this approach we refined the group contributions for the calculation of the heat capacities of liquid polycyclic aromatic hydrocarbons at 298.15 K and found a way to consider the effect of temperature on difference between the liquid and solid states heat capacities in the range of recalculation.