What are reactions?
Chemical reactions create new substances.
Chemical reactions can also be used to transfer energy by burning fuels.
In a chemical reaction the atoms rearrange themselves and then join back together in a different way.
How are chemical reactions used?
Chemical reactions make new substances. During a reaction energy is transferred to, or from, the surroundings. It is very difficult to reverse a chemical reaction and get back the starting substances.
We use chemical reactions to make useful products, including meals, medicines and makeup. Some chemical reactions are used for the energy they produce. For example, we can burn methane to help cook food and we can burn petrol to power vehicles. However not all chemical reactions are useful, including those that make food stale, or iron rusty.
In a chemical reaction the atoms in the starting substances separate from each other. They rearrange themselves and join together differently to make new substances called products. The number of atoms of each type is the same before and after a reaction. This means that the total mass of the products is the same as the total mass of the starting substances. In other words, mass is conserved.