Melting, Boiling, Freezing
Heat and cool to change states
What this lesson covers
Why it matters
Heat ice and it melts; heat water and it boils. Each step doesn't change WHAT the substance is — only how much energy its particles carry and how far apart they spread.
Predict first
What happens to the particles of a solid as you heat it toward a gas?
Heating gives particles energy: a solid's locked particles break free to slide (liquid), then fly apart (gas). Same particles throughout — a physical change.
- They gain energy and spread further apart — correct
- They lose energy and pack closer together
- They turn into different particles
What you do
Follow one splash of water from the freezer to the kitchen air. Arrange the five moments of its journey in order.
Check yourself
Going from liquid to gas (boiling), the particles…
Boiling adds energy so particles break free and spread out — still the same molecules.
Which state has the LEAST energetic particles?
In a solid, particles only vibrate in fixed positions — the lowest-energy state.
- gain energy and move much further apart — correct
- lose energy and pack together
- become brand-new molecules
- Solid — correct
- Liquid
- Gas