Alkanes are used as fuels because they release a large amount of energy when they undergo combustion.

They also store a large amount of energy for a small amount of weight.

Combustion is the reaction between a fuel and oxygen, resulting in the release of energy as heat.

In complete combustion, there is a plentiful supply of oxygen so the fuel reacts completely to form carbon dioxide and water vapour.

In incomplete combustion, there is an insufficient supply of oxygen so the fuel doesn't react completely, producing carbon monoxide and water vapour

Incomplete combustion can also produce solid carbon (soot).

Incomplete combustion occurs when there is insufficient oxygen for the fuel to react completely.

This happens with longer chain alkanes which need more oxygen compared to shorter chains.

Hydrocarbon + oxygen ➔ carbon dioxide + water

The symbol equation for the complete combustion of propane is: C₃H₈ + 5O₂ ➔ 3CO₂ + 4H₂O.

Carbon monoxide, water vapour, carbon and unburnt hydrocarbons can be formed.

Carbon monoxide is poisonous and can prevent oxygen from binding to hemoglobin in the blood.

The low reactivity of alkanes is due to:

1. The strong C-C and C-H covalent bonds require a lot of energy to break.
2. The non-polar nature of C-C bonds make it difficult for alkanes to attract nucleophiles or electrophiles.