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

1 of 6: Calcium carbonate is made up of 28 grams of calcium oxide and 22 grams of carbon dioxide.

Example 1: step 2

2 of 6: To find out the amount of calcium carbonate, add the 28 grams of calcium oxide and 22 grams of carbon dioxide.

Example 1: step 3

3 of 6: This makes a total of 50g of calcium carbonate.

Example 2: step 1

4 of 6: 48 grams of magnesium and an unknown amount of oxygen make 80 grams of magnesium oxide.

Example 2: step 2

5 of 6: Take the 80 grams of magnesium oxide and take away the 48 grams of magnesium.

Example 2: step 3

6 of 6: This leaves 32 grams of oxygen.


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.

BiogasBacteria break down sewage in a digesterThe methane in biogas can be used as a fuel for heating homes
BioethanolYeast breaks down the sugar in sugar cane to produce alcoholBioethanol is used in Brazil to fuel cars
Fast-growing timberTrees such as willow can be burned in power stationsElectricity is generated using renewable biomass instead of fossil fuels
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