Changes of state - AQA GCSE Physics Exam Questions

Practise 21 exam-style questions on Changes of state for AQA GCSE Physics. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

21 questions
1–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

On a warm day, a puddle of water slowly disappears. On a cold morning, droplets of water form on the inside of a bedroom window.

Name the change of state in each case.

Model answer

The puddle disappears by evaporation. The droplets form on the window by condensation.

Explanation

Evaporation turns a liquid into a gas at its surface, at temperatures below its boiling point. Condensation is the reverse: water vapour in the warm room air turns back into liquid water when it touches the cold glass.

Mark scheme

1 mark
puddle: evaporation / evaporating
do not accept boiling
1 mark
window: condensation / condensing

Question 2

2 marks

Which two of these are physical changes?

burning wood
melting butter
rusting iron
boiling water
frying an egg

Model answer

Melting butter and boiling water.

Explanation

Melting and boiling are changes of state, so they are physical changes: cooling the liquid butter or condensing the steam gives back the original substance. Burning, rusting and frying make new substances, so they are chemical changes.

Mark scheme

1 mark
melting butter
if more than two answers are given, deduct 1 mark for each wrong answer
1 mark
boiling water

Question 3

3 marks

A plastic bottle is filled completely with water, sealed, and put in a freezer. When the water freezes, the bottle bulges outwards.

State and explain what happens to the mass and to the volume of the water when it freezes.

Model answer

The mass stays the same, because the bottle is sealed and the water molecules are not created or destroyed when they freeze. The volume increases, because ice is less dense than liquid water: the same mass of water takes up more space as ice, so it pushes the sides of the bottle outwards.

Explanation

Mass is conserved in a change of state, but volume and density can change. Water is unusual because it expands when it freezes - which is why pipes can burst in winter.

Mark scheme

1 mark
the mass stays the same because no water is added or removed / particles are not created or destroyed
1 mark
the volume increases
1 mark
because ice is less dense than liquid water, so the same mass takes up a larger volume
allow the molecules in ice are arranged with more space between them

Question 4

4 marks

0.92 kg of water freezes to form ice.
The density of liquid water is 1000 kg/m³.
The density of ice is 920 kg/m³.

Calculate the increase in volume when the water freezes.

Model answer

Mass is conserved, so the ice also has a mass of 0.92 kg.
Volume of water = m ÷ ρ = 0.92 ÷ 1000 = 9.2 × 10⁻⁴ m³
Volume of ice = m ÷ ρ = 0.92 ÷ 920 = 1.0 × 10⁻³ m³
Increase in volume = 1.0 × 10⁻³ − 9.2 × 10⁻⁴ = 8.0 × 10⁻⁵ m³

Explanation

The key idea is that mass does not change when a substance changes state. Use volume = mass ÷ density for each state, then subtract. The volume increases by about 9%.

Mark scheme

1 mark
the mass of the ice is also 0.92 kg (mass is conserved)
may be implied by using 0.92 kg for the ice; an answer of 8.0 × 10⁻⁵ m³ scores 4 marks
1 mark
volume of water = 0.92 ÷ 1000 = 9.2 × 10⁻⁴ (m³)
allow 0.000 92 m³
1 mark
volume of ice = 0.92 ÷ 920 = 1.0 × 10⁻³ (m³)
allow 0.001 m³
1 mark
increase = 8.0 × 10⁻⁵ (m³)
allow 0.000 08 m³ or 80 cm³; allow ecf

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