Compensation relationship in thermodynamics of vaporization of aromatic and aliphatic compounds and their heat capacities

• Published in: Journal of molecular liquids Vol. 390; p. 123075
• Main Authors: Yagofarov, Mikhail I., Solomonov, Boris N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-11-2023
• Subjects: Compensation relationship; Heat capacity; Trouton’s rule; Vapor pressure; Vaporization enthalpy; Vaporization entropy; vaporization Gibbs energy; Vapor pressure; Vaporization enthalpy; Compensation relationship; Heat capacity; Trouton’s rule; Vaporization entropy; vaporization Gibbs energy
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.123075

•Coefficients of vaporization Gibbs energy-enthalpy correlation were derived;•Effects of boiling entropy and heat capacity on compensation relationship were analyzed;•Possible limits of the compensation relationship coefficients were established;•Reasons for difference between the relationships for aliphatics and aromatics are found.
It is long known that there is a correlation between the Gibbs energies and enthalpies of many processes, particularly solvation and vaporization, which is called the compensation relationship. Recently, we established that the correlation between the Gibbs energies and enthalpies of vaporization of non-hydrogen-bonded organic non-electrolytes at 298.15 K is divided into the two linear relationships with different slopes in the cases of aromatic and long-chain aliphatic compounds. We also recently found that there is a correlation between the difference between the heat capacities of the liquid and ideal gas, on the one hand, and the vaporization enthalpy at 298.15 K. Similarly with the compensation relationship, it is different in the cases of aromatic and aliphatic compounds.
In this work, our goal was to establish the factors defining the values of the coefficients of the Gibbs energy-enthalpy correlation and understand its features in aromatic and aliphatic compounds. The thermodynamic analysis enabled to independently determine the coefficients of the compensation relationship, investigate their possible boundaries, and explicitly show how they depend on the difference between the heat capacities of the liquid and ideal gas and boiling entropy. Slight variations in the boiling entropy of non-hydrogen-bonded compounds appeared to have almost no effect on the compensation relationship, while the difference in the slopes exhibited by aromatic and aliphatic molecules was due to the features of the heat capacity-enthalpy dependence.