Revision of the Thermodynamics of the Proton in Gas Phase

Abstract

Proton transfer is ubiquitous in various physical/chemical processes, and the accurate determination of the thermodynamic parameters of the proton in the gas phase is useful for understanding and describing such reactions. However, the thermodynamic parameters of such a proton are usually determined by assuming the proton as a classical particle whatever the temperature. The reason for such an assumption is that the entropy of the quantum proton is not always soluble analytically at all temperatures. Thereby, we addressed this matter using a robust and reliable self-consistent iterative procedure based on the Fermi-Dirac formalism. As a result, the free proton gas can be assumed to be classical for temperatures higher than 200 K. However, it is worth mentioning that quantum effects on the gas phase proton motion are really significant at low temperatures (T ≤ 120 K). Although the proton behaves as a classical particle at high temperatures, we strongly recommend the use of quantum results at all temperatures, for the integrated heat capacity and the Gibbs free energy change. Therefore, on the basis of the thermochemical convention that ignores the proton spin, we recommend the following revised values for the integrated heat capacity and the Gibbs free energy change of the proton in gas phase and, at the standard pressure (1 bar): ΔH0→T = 6.1398 kJ mol(-1) and ΔG0→T = -26.3424 kJ mol(-1). Finally, it is important noting that the little change of the pressure from 1 bar to 1 atm affects notably the entropy and the Gibbs free energy change of the proton.

Proton-Coupled Electron Transfer in the Reaction of 3,4-Dihydroxyphenylpyruvic Acid with Reactive Species in Various Media

“…Our calculated gas phase free energy of the proton is Δ ∘ (H + ) = −26.26 kJ/mol. Similar results were also proposed recently [46,47]. Solvation free energies of H atom in studied solvents were taken from published solvation free energies and entropies listed in [48][49][50] and reported in Table 1.…”

Antioxidative Potency and UV–Vis spectra features of the compounds resulting from the chelation of Fe2+ by Caffeic Acid Phenethyl Ester and two of its derivatives

“…We absolutely need the enthalpy and free energy of H Å , H + and e À to determine these descriptors. We took the enthalpy of H + and e À to be respectively 6.1398 kJ/mol [34] and 3.1351 kJ/mol [35] at temperature 298.15 K and pressure 1 atm. In the same condition their free energy was taken to be respectively À26.26 kJ/mol and À3.72 kJ/mol [33].…”

Large‐Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

“…(1). The gas-phase free energy and the gas-phase enthalpy of the proton have been reported previously by Fifen et al [39] Thus, we have located and optimized the most stable structures of neutral and protonated ammonia clusters for n = 30, 40, and 50. Then, the free energy and enthalpy of eq.…”