IB Physics SL B.1.8 Phase Changes Question Bank
Practise explaining melting, freezing, boiling and evaporation through molecular energy, bonds and constant-temperature graphs.
- Syllabus
- First assessment 2025
- Course
- Physics SL
- Level
- SL
Exam points
- Explain evaporation, boiling, melting and freezing through molecular motion, energy transfer and bonds.
- Interpret phase-change graphs and explain constant temperature while intermolecular potential energy changes.
- Distinguish evaporation from boiling using surface, pressure and molecular-energy conditions.
B.1.8—Phase change question 1
[Maximum number: 3]
The water in (b) is further heated until it starts to boil at constant temperature. It is boiled for 500 s measured from the time that it first starts to boil. The mass of water remaining after this time is 0.20 kg .
Explain, in terms of the energy of the molecules of the water, why the water boils at constant temperature.
All the thermal energy is used to separate the molecules / break the bonds between molecules.
It does not increase their average kinetic energy.
Average kinetic energy is a measure of the temperature of the water.
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