AQA GCSE Physics (8463), Higher tier · Particle model of matter › Changes of state and the particle model
Practise Changes of state. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Solid carbon dioxide is sometimes called ‘dry ice’. At room temperature, dry ice changes directly from a solid into a gas. What is the name of this change of state?
Sublimation
The student then put the bag into cold water. The bag became flat again. Name the change of state that happened.
Condensing
Name the change of state when ice changes directly into water vapour.
Sublimation
A pure substance melts at 63 °C. At what temperature will the same substance freeze?
63 °C
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) Solid carbon dioxide is sometimes called ‘dry ice’. At room temperature, dry ice changes directly from a solid into a gas. What is the name of this change of state?[1]
(b) Which change of state happens when water vapour turns into liquid water? Tick (✓) one box.[1]
Boiling
Condensing
Freezing
Melting
(c) A student put 45 g of ice into a plastic bag and sealed the bag. After one hour, all of the ice had melted. What was the mass of the water in the bag?[1]
(d) Give the reason for your answer.[1]
Show the answer and mark scheme
(a)Answer: Sublimation
sublimation / subliming / sublimating
(b)Answer: Condensing
(c)Answer: 45 g
45 (g)
(d)Answer: Mass is conserved in a change of state; the bag was sealed, so no particles could enter or leave.
mass is conserved when a substance changes state / no particles were added or removed because the bag was sealed
Question 2Medium6 marks
Melting, freezing, boiling, evaporating, condensing and sublimating are all changes of state.
(a) Changes of state are physical changes. Explain how a physical change is different from a chemical change.[2]
(b) A student boiled 250 g of water in an open beaker. After 5 minutes, the mass of water in the beaker was 212 g. The student said: ‘This shows that mass is not conserved when water boils.’ Explain why the student is wrong.[2]
(c) Describe how the arrangement and the movement of the particles change when a solid melts.[2]
Show the answer and mark scheme
(a)Answer: If a physical change is reversed, the material recovers its original properties; a chemical change produces a new substance with different properties.
in a physical change the material recovers its original properties if the change is reversed
in a chemical change a new substance (with different properties) is made
(b)Answer: The missing 38 g became steam that escaped into the air; the total mass of water plus water vapour is unchanged.
38 g of water turned into water vapour / steam which escaped from the open beaker (into the air)
the total mass of the water and the water vapour did not change / no particles were destroyed
(c)Answer: The particles go from a regular arrangement, vibrating about fixed positions, to a random arrangement in which they are still close together but can move past each other.
the arrangement changes from regular to random / irregular (the particles stay close together)
the particles change from vibrating about fixed positions to moving around / sliding past each other
Question 3Hard8 marks
A student put 0.50 g of liquid ethanol into a plastic bag, squeezed all the air out of the bag and sealed it. The student then put the bag into a bowl of very hot water. All of the ethanol evaporated and the bag inflated.
(a) The student measured the mass of the sealed bag before and after the ethanol evaporated. Predict what the student found. Give a reason for your answer.[2]
(b) The volume of the ethanol vapour in the bag was 310 cm3. Calculate the density of the ethanol vapour in kg/m3. Give your answer to 2 significant figures.[3]
(c) The density of liquid ethanol is 789 kg/m3. Use the particle model to explain why liquid ethanol is much denser than ethanol vapour.[2]
(d) The student then put the bag into cold water. The bag became flat again. Name the change of state that happened.[1]
Show the answer and mark scheme
(a)Answer: No change in mass: mass is conserved when a substance changes state, and no particles could leave the sealed bag.
the mass did not change
mass is conserved in a change of state / the number of ethanol particles did not change because the bag was sealed
(b)Answer: 1.6 kg/m3
mass = 5.0 × 10−4 kg and volume = 3.1 × 10−4 m3
density = 5.0 × 10−4 ÷ 3.1 × 10−4
1.6 (kg/m3)
(c)Answer: In the liquid the particles are touching; in the vapour they are far apart, so the same mass fills a far larger volume.
in the liquid the particles are close together / touching, but in the vapour they are far apart
so the same mass / number of particles takes up a much smaller volume in the liquid