Standardreduktionspotentialer

Standardreduktionspotentialer, or standard reduction potentials, are the electrical potentials associated with redox couples under standard conditions. They quantify the tendency of a chemical species to gain electrons and be reduced. In practice, standard conditions mean activities of all solutes equal to 1 (approximately 1 M for ions), a pressure of 1 atm for gases, and a temperature of 298 K.

The value, denoted E°, is defined for a half-reaction written as a reduction. The standard hydrogen electrode serves as the reference with E° = 0 V. A more positive E° indicates a greater tendency to be reduced relative to the hydrogen electrode; a more negative E° indicates a greater tendency to be oxidized.

Standard reduction potentials are used to predict the direction of redox reactions and to calculate cell potentials for electrochemical cells. The standard cell potential is E°cell = E°cathode − E°anode. The Gibbs free energy change under standard conditions relates by ΔG° = −nF E°cell, where n is electrons transferred and F is Faraday's constant.

Potentials depend on temperature and the activities of the participants; under nonstandard conditions, the Nernst equation describes how E shifts with concentrations and pH. Proton concentration often influences redox couples involving H+ or OH−, so E° values for such reactions are not directly transferable across pH.

Standardreduktionspotentialer tables are widely used in electrochemistry, corrosion science, battery technology and analytical chemistry to compare redox strengths of species, select reactions, and estimate feasibility of processes such as metal deposition or corrosion inhibition.