Combustion of Fuels
- Fuels are substances that react with oxygen to release energy
- This reaction is called combustion
- Due to the release of energy, combustion reactions are exothermic
- When there is plenty of oxygen for the fuel to burn in, complete combustion occurs
- In complete combustion, all of the elements within the fuel react fully with the oxygen
- Many fuels, such as natural gas and petrol, consist of hydrocarbons
- A hydrocarbon is an compound containing hydrogen and carbon atoms only
- When the hydrocarbon undergoes complete combustion:
- The carbon reacts with oxygen to form carbon dioxide, CO2
- The hydrogen reacts with oxygen to form water, H2O
Summary table of complete combustion reactions
| Fuel | Equation |
| Methane | methane + oxygen → carbon dioxide + water |
| Ethane | ethane + oxygen → carbon dioxide + water |
| Ethanol | ethanol + oxygen → carbon dioxide + water |
- You might be asked to balance chemical equations for combustion reactions
- The balanced symbol equation for the combustion of methane is:
CH4 + 2O2 → CO2 + 2H2O
- To balance combustion equations, balance the carbon atoms first, then the hydrogen atoms and finally the oxygen atoms
Photo by Bruno in Unsplash
Combustion is the burning of a fuel in oxygen
Worked example
Balance the symbol equation for the combustion of propane.
___C3H8 + ___O2 → ___CO2 + ___H2O
Answer:
- Balance the carbon atoms first
- There are 3 on the left hand side so place a 3 in front of carbon dioxide
- ___C3H8 + ___O2 → 3CO2 + ___H2O
- There are 3 on the left hand side so place a 3 in front of carbon dioxide
- The balance the hydrogen atoms
- There are 8 on the left hand side, so a 4 needs placing in front of water
- ___C3H8 + ___O2 → 3CO2 + 4H2O
- There are 8 on the left hand side, so a 4 needs placing in front of water
- Finally, balance the oxygen atoms
- There are now 10 oxygen atoms on the right hand side (6 from carbon dioxide, and 4 from water)
- A 5 needs placing in front of oxygen
- ___C3H8 + 5O2 → 3CO2 + 4H2O
