Heterogeneous oxidation reaction, diagram

Fig. 1. Diagram of heterogeneous oxidation reaction. Heat generation (1) and heat removal (2 -2" ) curves...

Figure 3.6.1 Outer-sphere and inner-sphere reactions. The inner sphere homogeneous reaction produces, with loss of H2O, a ligand-bridged complex (shown above), which decomposes to CrCl(H20) + and Co(NH3)5(H20). In the heterogeneous reactions, the diagram shows a metal ion (M) surrounded by ligands. In the inner sphere reaction, a ligand that adsorbs on the electrode and bridges to the metal is indicated in a darker color. An example of the latter is the oxidation of Cr(H20)5 at a mercury electrode in the presence of Cl or Br .

Heterogeneous electron transfer can be envisioned with the aid of transition state diagrams. First consider the forward reaction, the transfer of an electron from the electrode to the oxidized species in solution adjacent to the electrode. A transition state diagram will in the first place reflect the reactant and the product free energy. The reactants are the oxidized species in solution and the electron in... 

---