1Melting
Heating makes the particles vibrate faster. At the melting point they break out of their places and start to slide past each other.
melting point
Lesson 2.2 notes
Changes of state
Melting, freezing, evaporating, condensing and sublimation, explained by what the particles do.
2Changes of state
Melting, freezing, evaporating (or boiling) and condensing move a substance between states. Sublimation is solid straight to gas.
meltingfreezingevaporatingcondensingsublimation
3Heating ice to steam
While ice melts and water boils, the temperature stays the same: the energy goes into breaking the particles apart.
melting pointboiling point
4Evaporation
Evaporation happens at any temperature: the fastest particles escape from the surface. Boiling happens all through the liquid.
evaporatingboiling
5Condensing
When a gas cools, its particles slow down and join together as a liquid, like water on a cold can.
condensing
6Sublimation
Some solids turn straight into a gas. Dry ice (solid carbon dioxide) does this without ever melting.
sublimation
7Mass is conserved
Changes of state are physical changes. No particles are made or lost, so the mass stays the same, and the change can be reversed.
physical change
Explore: Heat it up
Drag the temperature slider and watch ice melt and water boil.
Common mistake: A flat line on a heating graph doesn't mean nothing is happening
The substance is changing state. The energy goes into breaking the particles free, so the temperature stays the same until the change is complete.
Remember
- Melting: solid → liquid. Freezing: liquid → solid. Evaporating and boiling: liquid → gas. Condensing: gas → liquid.
- During a change of state, the temperature stays the same.
- Changes of state are physical: mass is conserved and they can be reversed.
Going further at GCSE