Changing states

Solids, liquids and gases change state when they are heated or cooled.

When some solids are heated, they melt and turns into a liquid. For example, wax and ice melt when they are heated. The temperature this happens at is called the melting point, and it is measured in degrees Celsius (°C).

The melting point of ice (solid water) is 0 degrees Celsius (0°C). Different materials have different melting points. Chocolate melts at around 35°C.

When a liquid is cooled, it freezes and turns into a solid. For example, water freezes into ice in puddles on a very cold day. Freezing happens at the same temperature as the melting point.

When a liquid is heated it boils and turns into a gas. For example, if water is heated in a pan or in a kettle, it boils and turns into steam.

The temperature this happens at is called the boiling point. The boiling point of water is 100°C. The boiling point of ethanol (alcohol) is 78°C.

If you heat water slowly at a lower temperature than boiling point, then the water on the surface will evaporate. For example the Sun may heat up water in a puddle and it will slowly evaporate. The puddle may evaporate quicker on a very hot day, if it was windy or the water was spread out thinly across the surface.

When a gas is cooled, it condenses, and changes into a liquid. For example, the steam from a boiling pan turns into condensation on a cold window in the kitchen.

Condensing happens at the same temperature as the boiling point.

How many examples changing of states can you think of?

Try to think of at least 5 more. Record your results in a table like the one above.