FuelsCambridge IGCSE Chemistry: Revision notes
Section 1
What Are the Fossil Fuels?
The three fossil fuels are:
- Coal
- Natural gas
- Petroleum
Methane is the main constituent of natural gas. Petroleum itself is a mixture of hydrocarbons, and it is refined to produce most of the fuels we use.
Section 2
How Is Petroleum Separated into Fuel Fractions?
Petroleum is separated into useful fractions by fractional distillation. As you move up the fractionating column, the fractions collected show clear trends:
- Decreasing chain length
- Higher volatility
- Lower boiling points
- Lower viscosity
Each fraction is itself a mixture of similar-sized hydrocarbon molecules used for a different purpose.
Section 3
What Are the Fuel Fractions Used For?
Different fractions from petroleum are used as different fuels:
| Fraction | Use |
|---|---|
| Refinery gas | Heating and cooking |
| Gasoline/petrol | Fuel for cars |
| Kerosene/paraffin | Jet fuel |
| Diesel oil/gas oil | Diesel engines |
| Fuel oil | Ships and home heating |
(Naphtha, a non-fuel fraction, is used as chemical feedstock; lubricating oil and bitumen are used for lubricants/waxes and road-making respectively rather than as fuels.)
Notice the pattern: shorter-chain fractions (refinery gas, gasoline) are used where a fuel needs to ignite easily; longer-chain fractions (fuel oil) are used for heavier, slower-burning applications.
Section 4
How Does Ethanol Work as a Fuel?
Ethanol is also used as a fuel. Its combustion releases energy, and ethanol is used both as a solvent and as a fuel (sometimes blended with petrol).
Ethanol combustion (like other fuels) is exothermic and, when combustion is complete, produces carbon dioxide and water.
Complete combustion of ethanol: C2H5OH + 3O2 -> 2CO2 + 3H2O, releasing energy that can be used as fuel.
Must Know
- The three fossil fuels are coal, natural gas and petroleum
- Methane is the main constituent of natural gas
- Petroleum is separated by fractional distillation into fractions
- Moving up the column: decreasing chain length, higher volatility, lower boiling point, lower viscosity
- Key fuel fractions: refinery gas (heating/cooking), gasoline/petrol (cars), kerosene (jet fuel), diesel oil (diesel engines), fuel oil (ships/home heating)
- Ethanol is used as both a solvent and a fuel, and its combustion releases energy
That's the notes covered.
Carry on to the next subtopic.