Evaporation and boiling are both processes by which a liquid changes to a vapour. Describe TWO differences between evaporation and boiling.

Pearson Edexcel International GCSE Physics (4PH1) — 5.2 Change of state · Describe · 4 marks · View as Markdown

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

A puddle of water left on a pavement on a warm day gradually disappears, even though the water never reaches 100 °C.

Model answer (4 marks)

1. Evaporation can occur at any temperature, whereas boiling only occurs when the liquid reaches its boiling point.
2. Evaporation takes place only at the surface of the liquid, while boiling occurs throughout the entire volume of the liquid.

Examiner tips

Use the word ‘occurs’ to show the process, not just ‘takes place’.
Mention the temperature condition for boiling and the surface condition for evaporation.
Keep each point short and to the point to fit the 4‑mark limit.

Common mistakes

Confusing evaporation with condensation, or saying evaporation is the same as boiling.
Failing to state that boiling requires the liquid to reach its boiling point.

Mark scheme (4 marks)

Evaporation occurs at any temperature, whereas boiling only occurs at the boiling point of the liquid
Evaporation occurs only at the surface of the liquid, whereas boiling occurs throughout the whole liquid
During evaporation, only the higher-energy molecules escape from the surface, so the average kinetic energy of the remaining molecules decreases
Boiling requires a continuous external heat supply to maintain the boiling point temperature, whereas evaporation can occur without an external heat source

Key terms in this question

evaporation · boiling