Physical change Chemical change Law of conservation of mass
Learning Intentions
In this topic we are learning to: zz
zz zz Distinguish between physical and chemical changes.
Investigate whether mass is changed or unchanged when chemical and physical changes take place.
Verify the law of conservation of mass.
Matter can undergo physical and chemical changes. z z
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In a physical change, matter changes shape or state but no new substance is formed. Changing states, such as melting or boiling, are physical changes.
In a chemical change, a new substance is formed. All chemical reactions are examples of a chemical change.
The table below shows the differences between chemical and physical changes.
Physical changes
No new substance is formed Easy to reverse
Chemical changes
A new substance is formed Not easy to reverse
The Law of Conservation of Mass
The law of conservation of mass states that matter cannot be created or destroyed but can change from one form to another. In both physical and chemical changes, the total mass of matter stays the same.
Physical or chemical change?
With a partner, classify the following as either an example of a physical or a chemical change. Explain the reasons for your conclusion. (Hint: has a new substance been made? Is the reaction reversible?)
Boiling water in a kettle Burning wood in an open fire
A ball breaking a glass window Fireworks exploding Lighting a candle Baking a cake
Ice cream melting Dyeing your hair blonde z 166 166
Fig. 9.5.1 Fireworks exploding
Crushing up a plastic bottle A snowman melting An iron nail rusting
Getting a haircut
Tearing up a sheet of paper Sugar dissolving in water Photosynthesis
