Air and Combustion: Composition of Air and Burning Reactions

Composition of Air

Air is a mixture of gases: about 78% nitrogen, 21% oxygen, and small amounts of carbon dioxide, argon, water vapour and other gases.

What Is Combustion?

Combustion is a chemical reaction in which a substance (fuel) reacts rapidly with oxygen, releasing heat and light energy. Example: Carbon + Oxygen → Carbon dioxide + heat/light.

Types of Combustion

• Complete combustion: occurs with enough oxygen, producing carbon dioxide and water.
• Incomplete combustion: occurs with limited oxygen, producing carbon monoxide and/or soot (carbon), which is dangerous because carbon monoxide is poisonous.

Conditions for Combustion (Fire Triangle)

• Fuel (a combustible substance)
• Oxygen (to support burning)
• Heat (to raise the fuel to its ignition temperature)

Removing any one of these three puts out a fire - the basis of firefighting methods like smothering (removes oxygen) and cooling (removes heat).

Rusting and Air

Rusting of iron is a slow oxidation process that also requires oxygen and moisture from the air, though it is not combustion since it does not release heat/light rapidly.