Explain what happens to the internal energy of steam as it condenses into liquid water at 100 °C.

AQA GCSE Physics (8463) — 4.3.2 Internal energy and energy transfers · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

During condensation the internal energy of the steam decreases.
The released energy is given to the surroundings.
The temperature remains at 100 °C, so no change in kinetic energy.
The potential energy of the molecules falls as they come closer together and the intermolecular forces increase.

Examiner tips

Use the word ‘decreases’ for internal energy. Mention energy release to the surroundings. State that the temperature stays at 100 °C. Explain the drop in potential energy due to closer particle spacing.

Common mistakes

Saying the temperature rises or falls. Forgetting that kinetic energy remains unchanged. Using vague terms like ‘energy changes’ without specifying release or decrease.

Mark scheme (4 marks)

Internal energy decreases / is reduced during condensation
Energy is released / given out to the surroundings during condensation
The temperature does not change during condensation / remains at 100 °C
The potential energy of the particles decreases as particles move closer together / intermolecular forces change (kinetic energy stays the same)

Key terms in this question

internal energy