Redox Reactions

Redox reactions are among the most important types of chemical reaction. They are responsible for processes ranging from combustion and corrosion to photosynthesis and respiration. The name "redox" comes from reduction–oxidation, because the two processes always occur together.

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Definitions of Oxidation and Reduction

There are three equivalent ways to define oxidation and reduction. All three are valid and useful in different contexts:

In Terms of Oxygen

• Oxidation: Gain of oxygen
• Reduction: Loss of oxygen

In Terms of Electrons

• Oxidation: Loss of electrons (OIL)
• Reduction: Gain of electrons (RIG)

The mnemonic OIL RIG helps: Oxidation Is Loss, Reduction Is Gain.

In Terms of Oxidation States

• Oxidation: Increase in oxidation state
• Reduction: Decrease in oxidation state

All three definitions are consistent with each other. The electron transfer definition is the most general and applies to all redox reactions.

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Oxidising Agents and Reducing Agents

An oxidising agent (oxidant) is a substance that causes another substance to be oxidised. It does this by accepting electrons — so the oxidising agent itself is reduced.