You've seen loads of substances changing in your life.

Sometimes they change when they're heated: changes like melting and boiling are the result of heating.

Sometimes they change back when they're cooled: reversible changes are things like condensing and freezing.

Then again, you have often added substances to water and seen them dissolve. The question is - do they stay like that forever?

Do they go back to what they started like?

Can they be made to return to their original state or is the change permanent?

This series of questions will give you a chance to look over some basic changes, including when materials are heated and cooled.

Let's get started!