Changes of state and conservation of mass
Melting ice or boiling a kettle changes how particles behave — but not how many particles, or how much mass, there is.
Part of your national curriculum
- Chemistry: the particulate nature of matter: Understand changes of state in terms of the particle model, including conservation of mass
Lesson overview
What you'll learn in this lesson
Understand changes of state in terms of the particle model, including conservation of mass
Key learning points
- • Melting, freezing, evaporating, condensing
- • Changes of state are physical, not chemical
- • Conservation of mass
This lesson at a glance
- 24 minutes
- 17 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 17
Visual introductionPicture this
Changes of state and conservation of mass
Melting ice or boiling a kettle changes how particles behave — but not how many particles, or how much mass, there is.
In a nutshell
Understand changes of state in terms of the particle model, including conservation of mass
Learning cycle
Part 2 of 17
Learning cycle 1 of 2
Part 1 · Melting, freezing, evaporating, condensing
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 17
Learn
Melting, freezing, evaporating, condensing
When a solid is heated, particles gain energy and vibrate more until they break free of fixed positions — melting. Heating further gives liquid particles enough energy to escape entirely as a gas — boiling or evaporating. Cooling reverses these changes: condensing and freezing.
Reset break
Part 4 of 17
Pause
That's sitting 1 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 17
Learn
Changes of state are physical, not chemical
No new substances are formed during a change of state — only the arrangement and movement of existing particles changes. Water becoming ice is still made of the same H2O molecules; the change can be reversed by heating.
Quick check
Part 6 of 17
Quick check
Part 7 of 17
Reset break
Part 8 of 17
Pause
That's sitting 2 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 17
Learning cycle 2 of 2
Part 2 · Conservation of mass
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 17
Learn
Conservation of mass
Because no particles are created or destroyed during a change of state, the total mass stays the same. If 100 g of ice melts completely, you get exactly 100 g of water (though its volume changes slightly).
Quick check
Part 11 of 17
Reset break
Part 12 of 17
Pause
That's sitting 3 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 13 of 17
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 14 of 17
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
When a solid is heated, particles gain energy and vibrate more until they break free of fixed positions — ____.
Cooling reverses these ____: condensing and freezing.
Challenge round
Part 15 of 17
Game · Recall cards
What happens to particles when a solid melts?
Card 1 of 3
Mastery quiz
Part 16 of 17
Marked quiz
End of lesson quiz: Changes of state and conservation of mass
3 questions, marked with the reasoning shown. No timer.
1. What happens to particles when a solid melts?
2. Is melting a chemical or physical change?
3. 100 g of liquid water is frozen completely. What is the mass of the ice?
Lesson round-up
Part 17 of 17
Lesson round-up
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Understand changes of state in terms of the particle model, including conservation of mass