Combustion

Combustion is the burning of a fuel with the production of energy or heat

Examples of combustion reactions

1. Cellular respiration

Cellular respiration is the process whereby cells in our bodies obtain energy. Glucose reacts with oxygen producing carbon dioxide and water with the release of energy.

Glucose + oxygen => carbon dioxide + water + energy

C₆H₁₂O₆ + 6O₂ => 6CO₂ + 6H₂O + energy

2. The Combustion of fossil fuels

Fossil fuels are made up of hydrocarbons. Hydrocarbons are compounds that contain the elements hydrogen and carbon. Examples are methane, CH₄, propane, C₃H₈, butane, C₄H₁₀ and octane, C₈H₁₈

Hydrocarbons readily burn or undergo combustion reactions.Combustion may be complete or incomplete.

Complete combustion of fossil fuels results the production carbon dioxide and water. The incomplete combustion of fossil fuels results in the formation of carbon monoxide and soot (carbon).

1. Complete combustion of methane: Burns with a blue flame

Methane + oxygen => carbon dioxide and water

CH4 + 2O2 => CO₂ + 2H₂O

2. Incomplete combustion of methane producing carbon monoxide

Methane + oxygen => carbon monoxide and water

CH₄ + 1.5O₂ => CO + 2H₂O

3. Incomplete combustion of methane producing soot: Burns with a yellow flame

Methane + oxygen => carbon and water

CH₄ + O₂ => C + 2H₂O

As the amount of oxygen is decreased from 2 to 1.5 to 1 in the above three equations the combustion products respectively move from carbon dioxide to carbon monoxide to carbon or soot. As the soot is heated in the flame it produces a yellow flame. In real life there is a mixture of carbon monoxide and soot from the incomplete combustion of hydrocarbons as well as unburnt hydrocarbons.