Irreversible changes and the ‘fire extinguisher’

This resource is also available in Welsh and Irish

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This experiment focuses on using producing carbon dioxide to extinguish a candle. First watch the video showing the ‘fire extinguisher’ demonstration, then find out how to run the investigation with your learners.

Learning objectives

• To describe the difference between a reversible and an irreversible change.
• To explain that some changes result in the formation of new materials (in this case, one of these is carbon dioxide) and that this kind of change is not usually reversible.
• To understand that some gases are heavier than others.

Enquiry skills:

• To understand what variables are.

Watch the video

The video below shows how to carry out the ‘fire extinguisher’ demonstration.

What do learners need to know first?

Learners would benefit from investigating burning as an irreversible process.

Learners must understand the properties of solids, liquids and gases and the behaviour of the molecules in each state.

Learners should also have previously investigated reversible changes and be able to give scientific examples.

Learners should have some knowledge of fair testing and the effect of changing variables.

Equipment list

• Vinegar
• Bicarbonate of soda
• Long matches (short matches will work but long ones help avoid burnt fingers)
• Large jug (approx. 2 litre)
• Tea light candles
• Glass bowl (large enough to contain at least 5–6 tea lights for best effect)
• Dessert spoon
• Water/fire blanket (as a safety measure)