redox reaction
/ REE-doks /
When a slice of apple browns, a nail rusts, or wood burns, the same hidden bargain is going on: electrons change hands. One substance gives electrons away and another grabs them. A redox reaction is any reaction built on this transfer of electrons from one partner to another.
The name is a blend of the two halves that always come together. Reduction is gaining electrons; oxidation is losing them. The two cannot happen alone — every electron that one substance loses, another must pick up — so chemists pair them as a single redox event. A handy memory aid is OIL RIG: Oxidation Is Loss, Reduction Is Gain. The substance that takes electrons (and so gets reduced) is the oxidizing agent; the one that gives them up is the reducing agent.
Redox reactions are the engine of electrochemistry, but they are far broader than batteries. Respiration in your cells, photosynthesis in leaves, the bleaching of stains, and the smelting of metals from their ores are all redox chemistry. Whenever you can track electrons flowing from one species to another, you are watching reduction and oxidation at work.
When iron rusts, iron atoms lose electrons (oxidation) and oxygen gains them (reduction). The two changes are inseparable parts of one redox reaction.
Rusting iron: one partner loses electrons, the other gains them — that is redox.
Not every reaction is redox. Mixing acid and base, or dissolving salt, rearranges ions without changing how many electrons each atom owns — no oxidation state changes, so no redox.