3.6.2.1
During a phase change, potential energy changes but kinetic energy does not
Thermal Energy Transfer — AQA A-Level Physics
- Temperature stays constant during a phase change, so the average kinetic energyThe capacity to do work. Measured in joules (J).The energyThe capacity to do work. Measured in joules (J). an object possesses due to its motion. of particles does not change.
- The energyThe capacity to do work. Measured in joules (J). input changes the potential energy of the particles by altering their separation.
- Melting/boiling: energy input increases particle separation, overcoming intermolecular forces. Potential energy increases.
- Freezing/condensation: particles move closer together, intermolecular forces strengthen. Potential energy decreases.
- On a temperature-time graph, phase changes appear as horizontal plateaus.
Common Mistake
MEDIUM
Students often: Avoid saying that kinetic energyThe energy an object possesses due to its motion. changes during a phase change.
Instead: Temperature is constant during a change of state. Since kinetic energyThe energy an object possesses due to its motion. is proportional to temperature, kinetic energy does not change. Only potential energy changes.
Instead: Temperature is constant during a change of state. Since kinetic energyThe energy an object possesses due to its motion. is proportional to temperature, kinetic energy does not change. Only potential energy changes.