Term: Gibbs energy of activation (standard free energy of activation), \(\Delta ^{\ddagger}G^{\,\unicode{x26ac}}\)
https://doi.org/10.1351/goldbook.G02631

Definition:
The standard Gibbs energy difference between the transition state of a reaction (either an elementary reaction or a stepwise reaction) and the ground state of the reactants. It is calculated from the experimental rate constant k via the conventional form of the absolute rate equation: \[\Delta ^{\ddagger}G = R\ T\ \left[\ln (\frac{k_{\text{B}}}{h}) - \ln (\frac{k}{T})\right]\] where kB is the Boltzmann constant and h the Planck constant (kB/h = 2.08358 x 10E10 K-1 s ). The values of the rate constants, and hence Gibbs energies of activation, depend upon the choice of concentration units (or of the thermodynamic standard state).

Related Terms:
1) enthalpy of activation (http://doi.org/10.1351/goldbook.E02142).
2) entropy of activation (http://doi.org/10.1351/goldbook.E02150).
3) gibbs energy (http://doi.org/10.1351/goldbook.G02629).
4) transition state (http://doi.org/10.1351/goldbook.T06468).
5) elementary reaction (http://doi.org/10.1351/goldbook.E02035).
6) stepwise reaction (http://doi.org/10.1351/goldbook.S05970).
7) ground state (http://doi.org/10.1351/goldbook.G02704).
8) rate constant (http://doi.org/10.1351/goldbook.O04322).
9) boltzmann constant (http://doi.org/10.1351/goldbook.B00695).
10) planck constant (http://doi.org/10.1351/goldbook.P04685).
11) activation (http://doi.org/10.1351/goldbook.A00093).
12) standard state (http://doi.org/10.1351/goldbook.S05925).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1118 (https://doi.org/10.1351/pac199466051077)

Citation: 'Gibbs energy of activation (standard free energy of activation), \(\Delta ^{\ddagger}G^{\,\unicode{x26ac}}\)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.G02631

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