Note how the exchange current density of the forward and backward direction is different, exemplary displayed in Fig. , due to the different activities/coverages of the intermediates at equilibrium. Generally, the two Tafel exchange current densities (derived from the constant-coverage Tafel regions) will not have the same value except when the stoichiometric products of the oxidants and reductants at equilibrium (notably the intermediates) are equal for each step, as in Fig. and Fig. .