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Section 4: Heating and cooling materials

Learning objectives:

• heating some materials can cause them to change
• cooling some materials can cause them to change

IMPORTANT! Heating something is causing its temperature to rise. It is not setting it alight!!!

Some materials change when they are heated. Here are some examples:

• When you make a cake or biscuits the ingredients are mixed together and then placed in the oven, where they bake and become something you can eat.
• A slab of butter left lying in the sun will melt.
• When ice is warmed it changes into water.
• When you heat water, tiny droplets of water leave the container and enter the air. These tiny droplets are called water vapour. This process is called evaporation and is part of the water cycle.
• Water heated to boiling point (100°C) changes into a gas which we call water vapour.

If you melt something, you can usually reverse the change by putting the material somewhere cool to solidify again. Cooking something is an irreversible change - you can't get back the original material by leaving it in a cool place.

If you cool something by popping it in the freezer, you can usually reverse the change by leaving it at room temperature.

Which of these changes is irreversible?