Reduction: definition in chemistry
Reduction: Gain of electrons by a substance during a reaction, which decreases its oxidation number. It can also mean loss of oxygen or gain of hydrogen.
Reduction always happens together with oxidation, because the electrons gained must come from somewhere. The substance that gives up those electrons is called the reducing agent and is itself oxidized. Reduction is how most metals are obtained from their ores, for example when carbon monoxide removes oxygen from iron oxide in a blast furnace.
Examples
- Copper(II) ions gaining electrons to form copper metal: Cu²⁺ + 2e⁻ → Cu
- Iron(III) oxide reduced to iron by carbon monoxide in a blast furnace
- Chlorine gaining electrons: Cl₂ + 2e⁻ → 2Cl⁻
- Silver ions reduced to shiny silver metal when mirrors are made
On the periodic table
Nonmetals at the upper right of the table, especially fluorine, oxygen and chlorine, are reduced most easily because they readily gain electrons.