Burning Hydrocarbons – Complete and Incomplete Combustion

Complete combustion occurs when a hydrocarbon burns in excess oxygen. The only products are carbon dioxide (CO₂) and water (H₂O), plus energy in the form of heat and light. The flame is blue and produces no smoke or soot.

For example, methane burning completely: CH₄ + 2O₂ → CO₂ + 2H₂O. This is the ideal combustion reaction as it releases maximum energy and produces less harmful products (though CO₂ is still a greenhouse gas).

Incomplete combustion occurs when there is insufficient oxygen for complete burning. The products include carbon monoxide (CO), carbon/soot (C), and water. The flame is orange or yellow and produces visible black smoke.

For example: CH₄ + O₂ → CO + 2H₂O or CH₄ + O₂ → C + 2H₂O. This releases less energy than complete combustion and produces toxic carbon monoxide.

Carbon monoxide is extremely dangerous because it's colourless and odourless. It binds to haemoglobin in red blood cells more strongly than oxygen, preventing oxygen transport. This can cause headaches, dizziness, and death. Faulty boilers and car exhausts are common sources.

Carbon dioxide (CO₂) is a greenhouse gas. It traps heat in Earth's atmosphere, contributing to global warming and climate change. Burning fossil fuels releases large amounts of CO₂.

Carbon monoxide (CO) is a toxic air pollutant that affects human health. Soot (carbon particles) causes air pollution, reduces visibility, and can trigger respiratory problems like asthma. Both are produced by incomplete combustion in car engines and poorly maintained heating systems.