Irreversible changes

In a nutshell

Irreversible changes are permanent changes. These types of changes include: heating, the mixing of certain ingredients and some types of reactions.

Irreversible changes

Irreversible changes occur when a change cannot be undone and is permanent. Instead of returning to the original starting substance, a completely new material is created with different properties.

Types of irreversible changes

There are various types of irreversible changes you need to know about.

Irreversible change	EXPLANATION	example
Heating	When materials are heated they burn and turn to ash. The ash cannot be transferred back to the original material.	Wood is burnt to ash. The ash cannot be changed back to the wood.
Mixing of ingredients	The mixing of some ingredients is irreversible and they cannot be separated back out again.	Mixture of vinegar and bicarbonate of soda forming bubbles of carbon dioxide. The mixture cannot be separated back into the original two ingredients.
Reactions	The reaction between two substances, forming a different product. The original substances cannot be recreated.	The reaction of iron with oxygen to form rust (oxidation). The rust is a new material and the original part of the iron cannot be reformed.

Example

Cooking an egg is an irreversible reaction. The egg is heated up and fried. Once the egg has cooked, there is no way to reverse back to the raw egg material. So cooking the egg is an irreversible change.

Example

Explain why mixing the ingredients for a cake and baking the cake mixture are irreversible changes.

Science; Materials; KS2 Year 5; Irreversible changes

1.	Different ingredients are needed to make a cake.
2.	The ingredients are mixed together.
3.	The cake mixture is baked. There is no way to reverse the cake back to the original ingredients.