Kinetic limitations

Electrode potentials are thermodynamic quantities and depict nothing about how fast a redox reaction can occur. Straightforward electron transfer reactions (like in Mn³⁺/Mn²⁺) are supposed to be fast, but redox reactions in which covalent bonds are made or broken may be much slower. For instance, MnO₄^- MnO₂ the potential is well above that for the oxidation of water (in Table 1 see O₂/H₂O), but the expected reaction occurs very slowly and aqueous permanganate is usually employed as an oxidizing agent (even though it should always be standardized before make use of in volumetric analysis).

Kinetic problems can also influence redox reactions at electrodes while covalent substances are involved. For instance, a practical hydrogen electrode uses particularly prepared platinum with a high surface area to act like a catalyst for the dissociation of dihydrogen into atoms. On another metals a high overpotential might be experienced, like a cell potential significantly larger than the equilibrium value is essential for a reaction to take place at an appreciable rate.