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What is a chemical reaction?

Observing a chemical reaction in a laboratoryObserving a chemical reaction in a laboratorySubstances join with others to form new substances in what is called a chemical reaction. Reactions can take place naturally. For example, the food we eat is changed into energy through a series of chemical reactions inside our bodies. In industry, we use chemical reactions to create, for example, medicines, along with many other useful substances.

A cake’s ingredients before bakingA cake’s ingredients before baking

Chemical change

Baking a cake is an example of using chemical reactions to make things. The molecules that make up a cake’s ingredients—flour, eggs, butter and others—are re-arranged using energy (the heat of the oven) during the baking. The cake is chemically different from its ingredients.



Concrete, a mixture of sand, cement, rubble and waterConcrete, a mixture of sand, cement, rubble and waterSubstances can be mixed together to make new materials without a chemical reaction taking place. For example, sand, cement, rubble and water can be mixed together to make concrete. The molecules in these substances do not change.

In the Middle Ages people called alchemists studied chemical reactions. They tried (and failed) to convert ordinary metals like lead into precious metals such as gold.

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