Section 1 of 6Two kinds of fuel
Fossil fuels
- Fossil fuels Coal, natural gas (mostly methane) and the fuels from crude oil such as petrol, diesel and propane.
- They still supply over 80% of the world's energy.
Hydrogen
- Hydrogen Used in rocket engines and in fuel cells that power some cars and buses.
- It burns with oxygen in an exothermic reaction: 2H2(g) + O2(g) → 2H2O(l).
What a fuel does
- What a fuel does A fuel releases heat when burned, and that energy can be used directly or to generate electricity.
Section 2 of 6Hydrogen: advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Releases more energy per kilogram than any other fuel except nuclear fuels | Expensive to produce |
| Only product is water, so no carbon dioxide or particulates are released when it burns | Making it takes energy and is often by a process that gives off carbon dioxide |
| Can be used in fuel cells to produce electricity directly | Hard to store and transport; it is a gas that is kept compressed or as a liquid in high-pressure tanks |
| Raw material, water, is plentiful | Highly flammable and potentially dangerous |
Section 3 of 6Fossil fuels
Fossil fuel profile
Advantages
- Advantages Established technology and infrastructure, relatively cheap and easy to transport, and reliable in energy output.
Disadvantages
- Disadvantages Burning releases carbon dioxide, which contributes to climate change, plus other pollutants such as sulfur dioxide.
Finite supply
- Finite supply The rate at which they are extracted is much faster than the rate at which they form, so they are non-renewable on a human timescale.
Section 4 of 6Evaluating the fuels
1
Compare the energy released per kilogram: hydrogen is the greater.
2
Compare pollution at the point of use: hydrogen produces only water, whereas fossil fuels release carbon dioxide and other pollutants.
3
Compare production: hydrogen must be made using energy, whereas fossil fuels are extracted.
4
Compare storage and cost: hydrogen is more difficult to store and currently more expensive.
5
Make a justified decision, such as that hydrogen is promising only if made using low-carbon energy.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Fuel | A substance that releases energy, usually as heat, when it burns. |
| Fuel cell | A device that reacts hydrogen with oxygen to produce electricity directly. |
| Non-renewable | A resource that is used up faster than it can be replaced. |
| Fossil fuel | A fuel formed over millions of years from the remains of ancient organisms. |
| Exothermic | Releasing energy to the surroundings. |
Section 6 of 6Exam technique
1
Saying hydrogen is completely clean; making it often uses energy and can release carbon dioxide.
2
Writing that hydrogen is a renewable resource; it is a fuel that has to be produced, and its renewability depends on how it is made.
3
Claiming fossil fuels will never run out; they are finite.
4
Not giving both sides in a comparison question.