The formal reduction potential E red ⊖ ⊖ ′ is often a more convenient, but conditional, form of the standard reduction potential, taking into account activity coefficients and specific conditions characteristics of the reaction medium. Therefore, its value is a conditional value, i.e., that it depends on the experimental conditions and because the ionic strength affects the activity coefficients, E red ⊖ ⊖ ′ will vary from medium to medium. Several definitions of the formal reduction potential can be found in the literature, depending on the pursued objective and the experimental constraints imposed by the studied system. The general definition of E red ⊖ ⊖ ′ refers to its value determined when C red C ox = 1 . A more particular case is when E red ⊖ ⊖ ′ is also determined at pH 7, as e.g. for redox reactions important in biochemistry or biological systems.