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Extended · Practice questions · Evaporation

Lose the fast ones, lose the heat.

Six original Cambridge-style questions on what evaporation is, why escaping particles cool the liquid, the three things that speed it up, and how it differs from boiling.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
The reasoning examiners reward

Fastest leave the surface, average energy falls.

01
[2 marks]

State what evaporation is, including where in the liquid it occurs and at what temperatures it can happen.

  • Evaporation is a liquid changing to a gas at the surface of the liquid. ✓
  • It can happen at any temperature below the boiling point. ✓
02
Analysis
[3 marks]

Explain, in terms of particles, why a liquid cools down as it evaporates.

  • The fastest-moving (most energetic) particles at the surface escape from the liquid. ✓
  • This leaves behind particles with a lower average kinetic energy. ✓
  • A lower average kinetic energy means a lower temperature, so the liquid cools. ✓
03
Analysis
[2 marks]

A patient with a high fever is cooled by dabbing their forehead with a damp cloth. Explain how this helps to cool them.

  • Water from the cloth evaporates, with its fastest particles escaping and carrying energy away. ✓
  • This cools the cloth and skin, drawing energy from the patient, lowering their temperature. ✓
04
[3 marks]

State three changes that would increase the rate of evaporation of water from an open dish.

  • Increase the temperature. ✓
  • Increase the surface area of the liquid. ✓
  • Increase the airflow (draught) over the surface. ✓

Drier (less humid) air would also speed it up.

05
[2 marks]

State two ways in which evaporation differs from boiling.

  • Evaporation happens only at the surface; boiling happens throughout the liquid. ✓
  • Evaporation happens at any temperature below boiling; boiling happens only at the boiling point. ✓
06
Analysis
[3 marks]

Wet washing on a line dries much faster on a warm, windy day than on a cool, still day. Explain why, referring to two factors.

  • The warmth gives more water particles enough energy to escape, so evaporation is faster. ✓
  • The wind (airflow) carries the escaped particles away from the surface, stopping them returning. ✓
  • Both effects increase the rate of evaporation, so the washing dries faster. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.