redokspotensial

Redox potential, often abbreviated as Eh, is a thermodynamic quantity that describes the tendency of a chemical environment to acquire electrons (to be reduced) or to donate electrons (to be oxidized). It is measured as an electrical potential relative to a reference electrode, commonly the standard hydrogen electrode (SHE). The potential of a redox couple, E°, is defined under standard conditions (activities of 1 M, 25°C, 1 atm) and reflects the intrinsic driving force for electron transfer between the couple and the environment. The actual redox potential E depends on concentrations and the chemical composition of the system; in aqueous solutions it is also influenced by pH and temperature.

Measurement and relationships: The Nernst equation relates E to E° and the reaction quotient Q: E = E° − (RT/nF) ln Q. At 25°C this simplifies to E = E° − (0.05916/n) log Q. In biological and environmental contexts, the redox potential is often expressed as Eh, measured against a reference electrode such as Ag/AgCl, and is used together with pH to describe the redox state of a system.

Applications and significance: Redox potential governs the direction of redox reactions and the stability of oxidation states; it is important in corrosion science, battery chemistry, water treatment, and soil and sediment chemistry. In biology, cells couple redox reactions with electron transport chains, arranging biochemical processes by their redox potentials to extract energy. In environmental science, Eh and pH help determine metal mobility and the activity of microorganisms.

Limitations: Because many redox processes involve coupled protons or occur through multiple electron steps, a single Eh value may not fully describe a system. Observed potentials can shift with pH, ionic strength, temperature, and the specific media present.