Year 8 Science · Unit 3 · Lesson 1

What Is Change in Matter?

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Learning Goals

Classify everyday changes as physical or chemical and justify your answer.
Order changes from most to least reversible using evidence.
Apply the concept of change to a real-world Australian context.

Warm Up

Order the steps

The six everyday changes below are shuffled. Write their order in the "Most → Least Reversible" column, numbering them 1 (most reversible) to 6 (least reversible). Then classify each as Physical (P) or Chemical (C).

Reversibility rank (1–6)	Everyday change	P or C?
	Burning toast
	Melting butter in a pan
	Rusting nail left outside
	Dissolving sugar in water
	Boiling water for tea
	Baking a cake

Hint: consider whether you can get the original material back — and how easily.

Your Turn

Real-world context

An Australian family is camping in the Blue Mountains. Around their campfire, many changes happen at once: the wood burns and turns to ash and embers, water in a billy boils and steam rises, fat from sausages drips and sizzles, marshmallows soften and then char, and smoke drifts up into the air. Within a few minutes, a whole range of physical and chemical changes have occurred simultaneously.

(a) Identify at least two physical changes happening at the campfire. For each, explain the evidence that tells you no new substance was formed.

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(b) Identify at least two chemical changes happening at the campfire. For each, state the key evidence that tells you a new substance has formed.

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(c) CSIRO researchers studying bushfire recovery distinguish physical changes (heat evaporating water from soil) from chemical changes (vegetation burning). Why does this distinction matter for predicting ecosystem recovery?

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Wrap Up

In one sentence, what was the main idea of this lesson?