Electron levels of hydrated redox particles

We consider a redox reaction of h3drated iron ions shown in Eqn. 2—42  

The electron level in hydrated redox particles consists of the energy AGmt ( 0) required for the standard gaseous electron to combine with or to be released from the gaseous redox partides and the energy AG ,( 0) required for the redox particles to form their hydrate structures. Since the donor and acceptor levels of gaseous redox particles Pefi j/Fe, equal each other, the difference between the 

The reorganization of the hydrate structure occurs immediately after the electron transfer. Since the rate of electron transfer (about 10 seconds) is much faster than the rate of molecnilar vibration (about 10 seconds), the electron transfer occurs adiabatically while the hydrate structure is frozen. This is the 

The redox reaction of hydrated particles referred to the standard gaseous electron may be represented by the following four steps, as shown for a redox reaction of hydrated iron ions in Fig. 2-37  

Redox reaction cycle FeJ5 - Fejj + ei iD, - FeJ in aqueous solution solid arrow=adiabatic electron transfer, dotted arrow = hydrate structure reorganization X = reorganization energy ered.d = most probable donor level eox.a = most probable acceptor level. 

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As the localized electron level of hydrated redox particles distributes itself in a rather wide range, we may assume the presence of energy bands in which the redox electron level fluctuates the reductant particles form a donor band, and the oxidant particles form an acceptor band. The donor and acceptor bands overlap in the tailing of their probability densities as shown in Fig. 2-39. 

The nonpolarizable electrode may also be defined as the electrode at which an electron or ion transfer reaction is essentiaUy in equilibrium i. e. the electron or ion level in the electrode is pinned at the electron level of hydrated redox particles or at the hydrated ion level in aqueous electrolyte. In order for the electrode reaction to be in equilibrium at the interface of nonpolarizable electrode, an appreciable concentration of redox particles or potential determining ions must exist in the electrolyte. 

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