Redokspotentsiaali

Redokspotentsiaali, known in English as redox potential, is a measure of the tendency of a chemical species to acquire electrons and be reduced during redox reactions. It is expressed as an electrode potential, E, measured relative to a reference electrode such as the Standard Hydrogen Electrode (SHE) or a saturated calomel electrode. A more positive redokspotentsiaali indicates a stronger oxidizing agent and a greater tendency to gain electrons; more negative values indicate a stronger reducing agent.

Standard redokspotentsiaali, E°, is defined for the reduction of the oxidized form to the reduced form under standard conditions (concentrations 1 M, gas partial pressure 1 atm, temperature 25°C). Values are typically reported versus SHE.

The Nernst equation relates E to the actual activities or concentrations: E = E° − (RT/nF) ln Q, or at 25°C E = E° − (0.05916/n) log Q, where n is the number of electrons transferred and Q is the reaction quotient.

Applications and examples: Redokspotentsiaali is central in electrochemistry, corrosion science, environmental chemistry, and biochemistry. For example, the standard potentials for the O2/H2O couple is +1.23 V, and Fe3+/Fe2+ is +0.77 V (all versus SHE). In biology, cellular redokspotentsiaali refers to the balance of redox couples such as NAD+/NADH, GSH/GSSG, influencing metabolism and signaling.

Measurement and interpretation: In practice, redokspotentsiaali is determined by potentiometric measurements with reference electrodes, and predictive use relies on the Nernst relation and thermodynamics to estimate reaction spontaneity and energy yield.