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The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode (SHE), at: Temperature 298.15 K (25.00 °C; 77.00 °F); Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species; Unit activity for each solvent and pure solid or liquid species; and
Where is the standard reduction potential of the half-reaction expressed versus the standard reduction potential of hydrogen. For standard conditions in electrochemistry (T = 25 °C, P = 1 atm and all concentrations being fixed at 1 mol/L, or 1 M) the standard reduction potential of hydrogen is fixed at zero by convention as it serves of reference.
The electric potential also varies with temperature, concentration and pressure. Since the oxidation potential of a half-reaction is the negative of the reduction potential in a redox reaction, it is sufficient to calculate either one of the potentials. Therefore, standard electrode potential is commonly written as standard reduction potential.
The standard reduction potential is defined relative to the standard hydrogen electrode (SHE) used as reference electrode, which is arbitrarily given a potential of 0.00 V. However, because these can also be referred to as "redox potentials", the terms "reduction potentials" and "oxidation potentials" are preferred by the IUPAC.
During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it could actually be constructed by "[immersing] a platinum electrode into a solution of 1 N strong acid and [bubbling] hydrogen gas through the solution at about 1 atm pressure".
Reduction potentials of various reactions v; Oxidizing agent Reducing agent Reduction Potential (V)
Formal standard reduction potential; G. ... Overpotential; S. Sedimentation potential; Standard electrode potential ... Table of standard reduction potentials for ...
Common reference electrodes and potential with respect to the standard hydrogen electrode (SHE): Standard hydrogen electrode (SHE) (E = 0.000 V) activity of H + = 1 Molar; Normal hydrogen electrode (NHE) (E ≈ 0.000 V) concentration H + = 1 Molar; Reversible hydrogen electrode (RHE) (E = 0.000 V - 0.0591 × pH) at 25 °C