Science 17.06.2020

Learning focus: Reversible and irreversible reactions

(Adult support needed at the end)

Within all chemical reactions, a change may occur. There are two types of changes:

  • Reversible changes - where a change is made physically and can be undone or reversed. For example: freezing water to make ice.

  • Irreversible changes - where the change is made chemically and cannot be reversed into its original states. For example: baking a cake.

Watch these films (if you are able to)

Irreversible changes

A change is called irreversible if it cannot be changed back again. In an irreversible change, new materials are always formed. Sometimes these new materials are useful to us.


Heating can cause an irreversible change. For example you heat a raw egg

to cook it. The cooked egg cannot be changed back to a raw egg again.


Mixing substances can cause an irreversible change. For example, when vinegar and bicarbonate of soda are mixed, the mixture changes and lots of bubbles of carbon dioxide are made. These bubbles and the liquid mixture left behind, cannot be turned back into vinegar and bicarbonate of soda again.


Burning is an example of an irreversible change. When you burn wood you get ash and smoke. You cannot change the ash and smoke back to wood again.

Reversible changes A reversible change is a change that can be undone or reversed. If you can get back the substances you started the reaction with, that's a reversible reaction.

A reversible change might change how a material looks or feels, but it doesn't create new materials. Examples of reversible reactions include dissolving, evaporation, melting and freezing.

ACTIVITY: Have a go at the activities on the BBC website if you are able to: If you can’t access the internet, checking with an adult first, investigate reactions yourself.

Which of these changes are reversible or irreversible?