Standard electrode potential

Lore & Background

The basis for an electrochemical cell, such as the galvanic cell, is always a redox reaction that can be broken down into two half-reactions: oxidation at the anode and reduction at the cathode. Electricity is produced due to the difference of electric potential between the individual potentials of the two metal electrodes with respect to the electrolyte. Although the overall potential of a cell can be measured, there is no simple way to accurately measure the electrode/electrolyte potentials in isolation, as electric potential varies with temperature, concentration, and pressure.

Reader's Guide

Standard electrode potential is crucial for predicting the spontaneity of redox reactions. The larger the value of the standard reduction potential, the easier it is for the element to be reduced, making it a better oxidizing agent. For example, F2 has a standard reduction potential of +2.87 V, indicating it is reduced easily, while Li+ has −3.05 V, meaning it is not easily reduced and Li(s) is a good reducing agent. In a galvanic cell, a spontaneous reaction requires a positive cell potential (Ecell⊖ > 0), which corresponds to a negative Gibbs free energy (ΔGcell⊖ < 0). The cell potential is calculated as Ecell⊖ = Ecathode⊖ − Eanode⊖, where the cathode potential is the standard reduction potential and the anode potential is the standard oxidation potential. This framework allows chemists to design batteries and understand corrosion and electrolysis processes.

Did You Know?

• The standard hydrogen electrode (SHE) is defined as having a potential of 0.00 V and serves as a reference for measuring other electrode potentials.
• The oxidation potential of a half-reaction is the negative of its reduction potential, so standard electrode potential is commonly written as standard reduction potential.
• Electrode potentials are independent of the number of electrons transferred; they are expressed in volts, which measure energy per electron transferred.
• A reversible electrode is one that owes its potential to changes of a reversible nature, requiring the system to be close to chemical equilibrium and subjected to very small, slow solicitations.