In a previous post, ‘What’s the matter?’, we discussed the three states of matter and how matter can change from one state to another by heating and cooling it. Changes between the states of matter can also happen by mixing.
Let’s take salt as an example. If we mix salt (solid) with water (liquid) we will get a salt solution. The salt will dissolve in the water and we know it’s there because if we taste it, it tastes…yucky!! Is there a way we can get the salt back though after the water has dissolved it..? The answer is yes, we can.
If you heat the salt solution, the water will evaporate, leaving the salt behind, the water vapour can be cooled so that it condenses back to liquid form (water). This is a reversible change because we will get the salt and water back in their original forms.
Not all changes are reversible, those which cannot be reversed are called IRREVERSIBLE.
Irreversible changes are permanent. They cannot be undone.
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. Can you think of other examples?
Mixing can also cause an irreversible change, for example when we put in a vitamin (solid) into water (liquid). The vitamin fizzes up and is dissolved in the water, this is called effervescent reaction : it is the formation of gas bubbles in a liquid, by a chemical reaction. This is an irreversible change because no matter what we do we cannot get the vitamin back to its original solid form.
Now that you know all about reversible and irreversible changes click on the effervescent vitamin above to play a game to test your knowledge!
Ready for more fun?? Watch these videos and see if you can do these experiments at home! Click on the images below.
Till next time…