Sort It: Physical or Chemical?
Classify everyday changes based on reversibility and new substances
What this lesson covers
Why it matters
Crumple a sheet of paper and it's still paper. Set it alight and you get ash and smoke — something brand new. Telling these two kinds of change apart is a chemist's core skill.
Predict first
What is the sure sign that a change is chemical, not physical?
A physical change alters form or state with no new substance (often reversible). A chemical change makes a new substance — often signalled by heat, light, gas, or a colour or smell change.
- A new substance with new properties is formed — correct
- The shape or size changes
- It simply gets warmer or colder
What you do
Sort each change: physical (same substance) or chemical (a new substance forms)?
Check yourself
Which of these is a chemical change?
Curdled milk is a new substance; melting and breaking only change the form.
Boiling water is a physical change because…
No new substance forms — cool the steam and the same water returns.
- Curdling of milk — correct
- Melting of ice
- Breaking a glass
- the steam can condense back into the same water — correct
- a brand-new gas is created
- it produces lots of bubbles