If we can change the material back it is called a reversible change, if we cannot change the material back it is called an irreversible change.

Look at these examples:

If I cook popcorn kernels in the microwave to make popcorn, I cannot get the popcorn kernels back ever again. This is called an irreversible change.

If I melt some chocolate in the microwave to make liquid chocolate, I could cool the chocolate in a mould to make a solid bar of chocolate again. This is called a reversible change.

Can you decide whether the changes to these materials are reversible or irreversible changes?

1) Freezing water to make ice? [reversible change] 3) Burning charcoal bricks on a BBQ? [irreversible change] 5) Frying an egg? [irreversible change] 7) Burning gas on the cooker? [irreversible change]

2) Baking dough to make bread? [irreversible change]   4) Melting butter? [reversible change] 6) Melting ice-cream? [reversible change]   8) Melting ice cubes to make water? [reversible change]