The overpotential In experiments the stoichiometric products are rarely equal as demanded by the definition of the formal potential and the corresponding rate constant 𝑘 𝑘 ∘≀ in Eq. 4a. A more practical form of the B-V equation is employed, making use of the equilibrium potential, 𝐸 𝑒𝑞 , where the net reaction rate becomes zero. Using the condition 𝑖 𝑘 (𝐸 = 𝐸 𝑒𝑞 ) = 0 in Eq. 3c yields the relationship between 𝐸 𝑒𝑞 and 𝐸 𝑘 ∘≀ (Eq 8a), which is the Nernst equation for step 𝑘. Recalling the definition of the overpotential, 𝜂 = 𝐸 -𝐸 𝑒𝑞 , depicting the difference of the applied potential to the equilibrium potential (associated with an infinitely far away resting electrode that is not affected by electrode processes (equilibrium reference electrode in Fig. ), we use Eq. 8a to replace 𝐸 𝑘 ∘≀ with 𝐸 𝑒𝑞 in the analytical B-V equation (Eq. 3c). This yields a more common version of the B-V equation which we will call the equilibrium BV-equation (Eq. 8b), where the exchange current density for each step 𝑘, 𝑖 0,𝑘 , is also introduced according to Eq. 8c. The superscript * denotes the value of a quantity at the equilibrium electrode as opposed to its value on the WE denoted with the superscript 𝑆. It is emphasized here that 𝑖 0,𝑘 is proportional to the stoichiometric product of the reductants and oxidants involved in step 𝑘 raised in the power of (1 -𝛼 𝑘 ) and 𝛼 𝑘 , respectively. As such, it is 𝑘 𝑘 ∘≀ rather than 𝑖 0,𝑘 that is the fundamental kinetic descriptor of the reaction step, in the sense that it is a concentration independent parameter. A commonly employed alternative reference state for the forward and backward rate constant is that at equilibrium, 𝑘 𝑓/𝑏,𝑘 𝑒𝑞 . This is perfectly fine if one recalls that this rate "constant" contains an implicit dependence on the equilibrium concentrations of reductants and oxidants (Eq. 8d).