Combustion
Chemistry: AQA A Level, topic 5.2.3
Combustion
Combustion is a fancy name for burning. When you burn a hydrocarbon, you can have complete combustion or incomplete combustion.
Complete combustion
- Complete combustion gives a blue flame.
- Complete combustion produces only carbon dioxide and water.
Incomplete combustion
- Incomplete combustion gives an orange smoky flame.
- The orange colour is due to small particles of pure carbon glowing red hot.
- Incomplete combustion gives some carbon dioxide, some water, but also pure carbon, hydrocarbons, and carbon monoxide.
- Incomplete combustion is more likely with longer chain alkanes, as they need more oxygen to combust completely.
Harmful Effects of Combustion
Combustion can cause the production of some nasty chemicals.
The internal combustion engine
- The combustion of alkanes powers our cars via the internal combustion engine.
- Common impurities from the internal combustion engine are:
- Nitrous oxides (NOx).
- Unburned hydrocarbons.
- Carbon monoxide.
- Nitrous oxides react to form ozone at ground level.
- Ozone irritates eyes and can cause lung damage.
Flue gases
- Flue gases are the gases that come out of chimneys. They are also produced as industrial waste.
- Flue gases often contain sulfur dioxide.
- Sulfur dioxide dissolves in water to make sulfuric acid. This then falls as acid rain, which destroys trees and vegetation.
Removing these chemicals
- We can remove sulfur dioxide by reacting with calcium oxide or calcium carbonate.
- This is because sulfur dioxide is acidic and calcium oxide is basic. The balanced equation for the process is:
- CaO +SO2 → CaSO3
- Catalytic converters can remove unburned hydrocarbons and nitrous oxides from fuel.
Test yourself on Combustion
Why are flames of incomplete combustion orange?
What are the three additional products from incomplete combustion?
What can we use to remove unburned hydrocarbons and nitrous oxides?