Redoxreaktio

Redox reaction, or redoxreaktio, is a chemical reaction in which the oxidation states of atoms are changed by the transfer of electrons between species. In a redox process, one substance is oxidized (loses electrons) and another is reduced (gains electrons). The substance that donates electrons is called the reducing agent and is itself oxidized; the substance that accepts electrons is the oxidizing agent and is reduced.

Electrons can be transferred directly between reactants or via intermediate species. Redox reactions are characterized by a change in oxidation numbers and by conservation of mass and charge. They occur in many contexts, from corrosion and combustion to energy metabolism in living organisms.

To balance redox equations, chemists often use half-reactions: separate oxidation and reduction half-reactions, balance atoms and then electrons, and combine, ensuring electrons cancel. In electrochemical cells, electron transfer occurs through an external circuit, producing electrical energy.

Redox potential measures tendency to acquire electrons. Standard reduction potential E° indicates the favorability of reduction at standard conditions. Larger (more positive) E° values mean stronger oxidizing agents. The Nernst equation relates potentials to concentrations and temperature, helping predict reaction direction and cell voltage.

Common examples range from rusting of iron, where iron is oxidized by oxygen, to metabolic processes such as the oxidation of nutrients during respiration and the photosynthetic electron transport chain. Redox reactions underpin batteries, corrosion, electroplating, and many industrial and biological systems.