15 2.8 Properties of the combustion products
1Carbon dioxide, CO₂
Formed when
- Complete combustion of carbon-containing fuel
Properties
- Colourless, odourless; does not burn or support burning; denser than air; dissolves in water to form carbonic acid, H₂CO₃
Effect
- Greenhouse gas; contributes to global warming
2Carbon monoxide, CO
Formed when
- Incomplete combustion (lack of oxygen)
Properties
- Colourless, odourless, toxic
Effect
- Poisoning; binds haemoglobin
3Water vapour, H₂O
Formed when
- Burning hydrogen or hydrocarbons
Properties
- Condenses to droplets when cooled
Effect
- Harmless in small amounts
4Carbon (soot), C
Formed when
- Incomplete combustion of hydrocarbons
Properties
- Fine black solid
Effect
- Blackens surfaces, harms lungs
5Sulphur dioxide, SO₂
Formed when
- Burning fuel with sulphur impurities
Properties
- Colourless, choking odour; dissolves in water to give sulphurous acid (H₂SO₃)
Effect
- Acid rain, respiratory irritation
6Nitrogen oxides, NOₓ
Formed when
- Burning fuels containing nitrogen compounds, and engine heat
Properties
- NO is colourless and reacts with oxygen to form NO₂ (reddish-brown, pungent, choking); NO₂ dissolves in water giving nitrous and nitric acids
Effect
- Acid rain, smog, lung irritation
Equations: S + O₂ → SO₂; 2NO + O₂ → 2NO₂.
- Cross-cutting concept: stability and change. In every combustion the substances change but the total mass of products equals the total mass of the reactants (conservation of matter).
- Yet the products can change the environment and human health over time.