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Published November 1968 | public
Journal Article

On the slope of free energy plots in chemical kinetics

Abstract

In current electron-transfer theory, an activation free energy term, ΔF*, depends in a simple way on the "standard" free energy of reaction, ΔF^0', in the prevailing medium. Namely, ΔF* = (1/4)λ[1 + (ΔF^0'/λ)]^2, apart from small work terms; λ/4 is ΔF_0*, the value of ΔF* at (ΔF^0' = 0; and λ obeys a simple additivity property. As an exploratory step an equation of the same functional form is applied in the present paper to data on Brønsted slopes of 16 proton- and atom-transfer reaction series. Thereby, the instantaneous slope of a ΔF* vs. ΔF^0' plot is calculated to be (1/2)[1 + (ΔF^0'/4 ΔF_0*)]. Thus far the experimental results are consistent with this equation, but more data are needed. Other applications of the ΔF* equation, including one to the kinetic isotope effect, are also discussed. A rather approximate derivation of the above equation for atom and other transfers was given in an earlier paper of this series.

Additional Information

© 1968 American Chemical Society. (Received June 6, 1968) Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. This research was also supported by a grant from the National Science Foundation at the University of Illinois.

Additional details

Created:
August 19, 2023
Modified:
October 23, 2023