1Heating ice
Heat some ice and the temperature rises to 0 °C. Then it stays at 0 °C until all the ice has melted.
melting
Lesson 17.3 notes
Energy and changes of state
Melting, boiling and freezing: where the energy goes while the temperature stays the same.
2Flat while the state changes
On a heating curve the flat parts show a change of state: melting at 0 °C and boiling at 100 °C.
melting pointboiling point
3Where the energy goes
While ice melts, the energy frees particles from their fixed places. They don't move faster yet, so the temperature stays the same.
4Energy in, energy out
Melting, boiling and evaporating take energy in. Freezing and condensing give energy out.
freezingcondensingevaporating
5Freezing gives energy out
As liquid stearic acid freezes, it gives out energy. This keeps its temperature at 69 °C until it is all solid.
freezing point
6Sweating
Sweat evaporating takes energy from your skin, so you cool down.
7Ice in a drink
Melting ice takes in energy from the drink around it, so the drink gets colder.
Explore: Heat it, cool it
Heat ice until it melts and then boils, then cool it down again. Watch the particles, the thermometer and the graph.
Common mistake: The temperature does not rise while ice melts
Even though you keep heating, ice stays at 0 °C until it has all melted. The energy frees the particles from their fixed places instead of making them move faster.
Remember
- While a pure substance melts or boils, its temperature stays the same: the energy is changing its state.
- Melting, boiling and evaporating take energy in. Freezing and condensing give energy out.
- Sweating cools you because evaporating sweat takes energy from your skin.
Going further at GCSE