Heating and Cooling — Chemistry (Grade 7)

Define and explain Heating and Cooling in your own words
Use key terms such as melt accurately
Apply what you have learned to new examples and questions
Avoid the common mistakes learners make with this topic

This lesson focuses on Heating and Cooling: investigate how warming and cooling change materials, and how to test fairly.

Definition: Heating and Cooling

Investigate how warming and cooling change materials, and how to test fairly.

Key ideas

Heating and cooling can be reversed

Many changes caused by heating and cooling can be undone: melt ice and you get water, freeze the water and you get ice again. Chocolate melts in a warm hand and hardens again in the fridge, with no new material made. Not every change is reversible — once you bake a cake you cannot un-bake it — but melting and freezing are.

Solids keep their shape

A solid holds its shape wherever you put it: a wooden block is still a block in your hand, in a box or on the table. You can often change a solid's shape by squashing, bending or cutting it, but it will not flow into a new shape on its own. That is why buildings, furniture and toys are mostly made from solids.

Key term — melt: To change from a solid to a liquid when warmed, like ice turning to water.

Worked example: Heating and Cooling

Chocolate left in a warm car goes soft. What is this change called, and is it reversible?

Melting; yes, it is reversible because cooling the chocolate hardens it again.

Answer: Melting; yes, it is reversible because cooling the chocolate hardens it again.

Common mistakes

Saying heating always destroys materials Gentle heating often just changes the state of a material, like melting butter. The butter is still butter, and cooling turns it solid again.
Thinking melted ice has disappeared When ice melts, it turns into water — the material is still there, just in a different state. If you freeze the water, the ice comes back, which proves nothing was lost.

Practice

Pour 100 ml of water from a beaker into a bottle. What changes and what stays the same?

Think about shape and amount.

The shape changes to fit the bottle, but the amount (volume) of water stays the same.

You warm some butter and it melts. How could you prove the melted butter is the same material?

What happens if you cool it again?

Cool it down and it freezes back into solid butter, showing no new material was made.

Why is a chair a solid?

What happens to its shape when you move it?

It keeps its own shape wherever you put it and does not flow.

Name one solid and one liquid you used today.

Think about breakfast or getting dressed.

Any sensible pair, for example toast (solid) and milk (liquid).

Quick check

Heating and Cooling — quick check

Which of these best defines "melt"?

To change from a solid to a liquid when warmed, like ice turning to water.

Sand pours like a liquid. Explain why scientists still call each grain a solid.

Each grain keeps its own shape and does not flow; only the pile of grains moves.

Key takeaways

Heating and Cooling: investigate how warming and cooling change materials, and how to test fairly.
Heating and cooling can be reversed: Many changes caused by heating and cooling can be undone: melt ice and you get water, freeze the water and you get ice again.
freeze: To change from a liquid to a solid when cooled, like water turning to ice.
Watch out for: saying heating always destroys materials

← Melting and Freezing Back to Grade 7 chapters Related resources →