When a solid melts
Heat makes particles vibrate harder until they leave their places.
Warming ice
The particles of ice vibrate about fixed positions. Now we heat the ice slowly.
What happens to the vibrations as the ice gets warmer?
What this lesson covers
The idea
Heating makes a solid's particles vibrate more vigorously until they leave their positions and it becomes liquid; the minimum temperature at which a solid melts at atmospheric pressure is its melting point.
Warming ice
The particles of ice vibrate about fixed positions. Now we heat the ice slowly.
What happens to the vibrations as the ice gets warmer?
- They become more vigorous
- They stop
- They stay the same
Heat the ice
Heat the ice 5 °C at a time. Watch the particles and the thermometer. At what temperature does it start to melt?
The melting point
Heating makes a solid's particles vibrate more vigorously. At one stage they leave their positions: the attractions get weaker and the solid becomes a liquid. The minimum temperature at which a solid melts at atmospheric pressure is its melting point.
The melting point of ice is 0 °C.
- Ice at | What happens
- −20 °C to −5 °C | Particles vibrate more and more, but stay in their positions
- 0 °C | Particles leave their positions: the ice melts
Notes
Heating makes a solid's particles vibrate more vigorously until they leave their positions and it becomes a liquid. The minimum temperature at which a solid melts at atmospheric pressure is its melting point.
Check yourself
What happens to the particles of a solid when it is heated?
What is the melting point of a solid?
Ice is heated from −20 °C. At what temperature does it start to melt?
Answer: 0 °C
Ice melts at 0 °C: its melting point.
Why does a solid turn into a liquid at its melting point?
- They get bigger. Heating makes the particles move more. It does not make them bigger.
- They stop vibrating. Heating makes them vibrate more, not less.
- They vibrate more vigorously — correct. Yes. In the end they leave their positions.
- The minimum temperature at which it melts at atmospheric pressure — correct. Yes. Below it, the solid does not melt.
- The temperature at which a liquid boils. That is the boiling point.
- Any temperature at which the solid feels warm. It is one particular temperature: the lowest at which the solid melts.
- Its particles vibrate so vigorously that they leave their fixed positions — correct. Yes. The attractions get weaker and the particles can move.
- Its particles themselves melt into smaller pieces. The particles do not melt or break. They leave their fixed positions.
- Air gets in between its particles. No air gets in. The particles leave their positions because they vibrate so vigorously.