Changing state

How do we change the state of water?

• Ice into water, and water into water vapour: supply heat.
• Water into ice: put it somewhere cold, like a freezer. The water freezes into ice. Take the ice out and it melts back into water.

Water is not the only example. A candle is made of wax: heat turns the wax liquid, and cooling turns it solid again. Coconut oil can turn solid in winter.

So substances change their state on heating or cooling. The change of a solid into a liquid is called melting. The change of a liquid into a solid is called freezing.

Put the four changes in a circle:

• a solid melts and becomes a liquid;
• the liquid evaporates and becomes a gas;
• the gas condenses and becomes a liquid again;
• the liquid freezes and becomes a solid.