Melting, boiling and evaporation Cambridge IGCSE Physics (9–1) revision
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In plain words
Heat ice and it warms up, until it reaches 0 °C. Then the temperature sticks there, however hard you heat, until every bit has melted. The energy isn't making the particles move faster any more: it's pulling them apart.
Three things to know
- While a substance melts or boils its temperature stays constant: the energy breaks the bonds between the particles instead of making them move faster.
- Boiling happens at one temperature (the boiling point), throughout the liquid, with bubbles. Evaporation happens at the surface, at any temperature.
- In evaporation the fastest particles escape, so the average energy of those left behind falls: the liquid cools. Evaporation is faster when it is warmer, when there is a larger surface area, and when there is a draught.
Tips and tricks
- Evaporation happens at any temperature and only at the surface. Boiling happens at one temperature, all through the liquid.
- "The most energetic particles escape, so the average energy of the rest falls" is the full reason evaporation cools.
It lands in your notebook with its questions as flashcards.
Melting, boiling and evaporation: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What happens to the temperature of water while it is boiling?
The energy goes into separating the particles.
Which is true of evaporation but not of boiling?
Boiling happens throughout the liquid, at the boiling point.
Why does evaporation cool a liquid?
The average energy of the particles left behind falls.
Which change makes a liquid evaporate faster?
Moving air carries away the particles that have escaped.
What is the change from liquid to solid called?
It happens at the same temperature as melting.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Melting, boiling and evaporation
Cambridge IGCSE Physics (9–1) 0972 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain why the temperature of ice stays at 0 °C while it melts, even though it is being heated.[2]
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The energy is used to break the bonds holding the particles in place, not to increase their kinetic energy.
Explain why sweating cools the body.[2]
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The sweat evaporates: the most energetic particles leave, taking energy from the skin.
Give three things that make a puddle evaporate faster.[3]
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A higher temperature, a larger surface area, and wind (a draught) across the surface.
Answers: Melting, boiling and evaporation
- 1. The energy is used to break the bonds holding the particles in place, not to increase their kinetic energy.
- 2. The sweat evaporates: the most energetic particles leave, taking energy from the skin.
- 3. A higher temperature, a larger surface area, and wind (a draught) across the surface.