Fuels
A fuel is any compound which has stored energy. Combustion is burning a fuel in oxygen, which gives out heat energy and is called an exothermic reaction. Our main source of fuel is from fossil fuels.
Conservation of mass
When things burn, it looks like they are destroyed, but during any chemical reaction no particles are created or destroyed. The atoms in fuels are simply rearranged from the reactants to the products during combustion. The products may have different properties to the reactants.
Mass is never lost or gained in chemical reactions. We say that mass is always conserved. In other words, the total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning.
Example 1: step 1
Example 1: step 2
Example 1: step 3
Example 2: step 1
Example 2: step 2
Example 2: step 3
Biomass
Biomass is biological material that has been recovered from once-living organisms. It can be used as a source of biofuels (a renewable energy source) to reduce our dependence on fossil fuels, and to help reduce air pollution. Using biomass as fuel still puts carbon dioxide back into the atmosphere, but it's the same carbon dioxide taken from the air as the biomass was produced. The use of biomass for energy production is carbon neutral.
| Examples | Processing | Use |
|---|---|---|
| Biogas | Bacteria break down sewage in a digester | The methane in biogas can be used as a fuel for heating homes |
| Bioethanol | Yeast breaks down the sugar in sugar cane to produce alcohol | Bioethanol is used in Brazil to fuel cars |
| Fast-growing timber | Trees such as willow can be burned in power stations | Electricity is generated using renewable biomass instead of fossil fuels |