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Practice questions · Changes of state

When the thermometer pauses.

Six original Cambridge-style questions on naming the changes of state, why the temperature holds steady while a substance melts or boils, reading a heating curve, and how boiling differs from evaporation.

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 points to nail every time

Energy can change state or change temperature.

01
[3 marks]

Name the change of state in each case:

(a) a solid turning into a liquid, [1] (b) a gas turning into a liquid, [1] (c) a liquid turning into a solid. [1]

(a) Melting. ✓

(b) Condensation (condensing). ✓

(c) Freezing (solidifying). ✓

02
Analysis
[2 marks]

While a pure solid is melting, energy is still being supplied to it, yet its temperature does not change. Explain why.

  • The energy supplied is used to break the bonds holding the particles in fixed positions, separating them. ✓
  • It is not used to make the particles move faster, so the temperature stays constant. ✓
03
Analysis
[2 marks]

A heating curve for a substance shows the temperature rising, then a flat horizontal section, then rising again. State what is happening during the flat section, and what stays constant.

  • During the flat section the substance is changing state (melting or boiling). ✓
  • The temperature stays constant throughout the flat section. ✓
04
[2 marks]

State two ways in which boiling differs from evaporation.

  • Boiling happens throughout the liquid; evaporation happens only at the surface. ✓
  • Boiling happens only at the boiling point; evaporation happens at any temperature below boiling. ✓

Boiling also produces bubbles and is faster.

05
Analysis
[2 marks]

On a cold day, droplets of water form on the inside of a window in a warm, steamy kitchen. Name the change of state taking place, and explain how it happens.

  • Condensation. ✓
  • Warm water vapour in the air touches the cold glass, loses energy, and changes back into liquid water droplets. ✓
06
Analysis
[2 marks]

When water freezes into ice, energy is transferred. State whether energy is taken in or given out, and explain in terms of the particles.

  • Energy is given out (released) to the surroundings. ✓
  • The particles slow down and form bonds into a fixed solid arrangement, releasing energy as they do so. ✓

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.