The Frequency Factor for Outer-Sphere Electrochemical Reactions.
PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
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The conventional formulation of the frequency factor A sub ne for outer-sphere electrochemical reactions based on a collisional model is compared with an alternative encounter preequilibrium treatment whereby An is determined by the effective frequency of surmounting the free energy barrier within a previously assembled precursor state. The latter model is shown to provide a more appropriate description for electrochemical reactions under most conditions, in harmony with analogous considerations for homogeneous redox processes. Noticeably ca. 20-fold larger values of A sub ne are derived from the encounter preequilibrium as compared to the collisional model. Numerical relationships between the kinetics of corresponding electrochemical and homogeneous reactions and of competing inner- and outer-sphere electrochemical pathways that are significantly different from the conventional relations are also predicted on the basis of the encounter preequilibrium model. The relationships between A sub Ne and experimental frequency factors obtained from the temperature dependence of electrochemical rate constants are also considered in the light of these considerations.
- Physical Chemistry
- Nuclear Physics and Elementary Particle Physics