Compare — 5 marks
A student is investigating the properties of water in different states of matter. They observe ice melting in a beaker on a hot plate and steam rising from boiling water. They want to understand how the particle arrangement and movement differ between these states.
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(a) Compare the arrangement of particles in ice and liquid water.
[2 marks]
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(b) Compare the movement of particles in liquid water and steam.
[2 marks]
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(c) Explain why ice has a fixed shape but steam does not, using your knowledge of particle arrangement.
[1 mark]
Show mark scheme
- (a) In ice, particles are arranged in a fixed/regular pattern/lattice (1 mark)
- (a) In liquid water, particles are arranged randomly/closely packed but not in a fixed pattern (1 mark)
- (b) In liquid water, particles vibrate/move around fixed positions with limited movement (1 mark)
- (b) In steam, particles move rapidly/freely in all directions with much greater movement/kinetic energy (1 mark)
- (c) Ice has fixed shape because particles are held in fixed positions by strong forces, while steam has no fixed shape because particles move freely and are not held in place (1 mark)
Describe — 2 marks
A student is making ice cream at home. They place a mixture of cream and sugar into a metal bowl and surround it with a mixture of ice and salt. After 20 minutes, the mixture in the bowl has changed from a liquid to a solid.
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Describe what happens to the arrangement of particles as the ice cream mixture changes from a liquid to a solid.
[2 marks]
Show mark scheme
- Particles move closer together / particles arrange in a regular/fixed pattern (1 mark)
- Particles vibrate in fixed positions / particles have less/reduced kinetic energy (1 mark)
Define — 3 marks
A student is investigating the water cycle in a sealed container. They heat water in a beaker and observe steam rising. After several hours, they notice water droplets forming on the inside of the container lid.
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(a) Define the term 'evaporation'.
[1 mark]
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(b) Define the term 'condensation'.
[1 mark]
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(c) Explain why the water droplets on the lid provide evidence that both evaporation and condensation have occurred in the sealed container.
[1 mark]
Show mark scheme
- (a) Evaporation is the change of state from liquid to gas (or vapour) / Process where particles with sufficient energy escape from the surface of a liquid
- (b) Condensation is the change of state from gas (or vapour) to liquid / Process where gas particles lose energy and form a liquid
- (c) Water evaporated from the beaker to form steam/water vapour; the water vapour then condensed on the cooler lid surface to form liquid water droplets
Compare — 4 marks
A student investigates the melting of ice and the boiling of water in a sealed container. They measure the mass of ice before heating and the mass of steam produced after boiling. They also observe that the volume of the container remains constant throughout the experiment.
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(a) Compare the mass of the ice before melting with the mass of water produced after melting. Explain your answer using the particle model.
[2 marks]
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(b) Compare the arrangement and motion of water particles in liquid water with their arrangement and motion in steam. Explain how the spacing between particles changes during boiling.
[2 marks]
Show mark scheme
- (a) The mass remains the same / does not change during melting
- (a) The number of particles remains constant / particles are not created or destroyed during the change of state
- (b) In liquid water, particles are close together / in contact / have little space between them; in steam, particles are far apart / have large spaces between them
- (b) In liquid water, particles vibrate in fixed positions / have limited motion; in steam, particles move rapidly and randomly in all directions / move freely throughout the container
Describe — 4 marks
An ice cube is removed from a freezer at -18°C and placed in a beaker on a hot plate. The beaker is heated steadily, and a student observes the ice gradually melting into water, which then begins to boil. The student measures the temperature throughout the process and notes that the temperature remains constant during both melting and boiling, even though heat energy is continuously being supplied.
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(a) Describe what happens to the arrangement and motion of particles as the ice melts into water at 0°C.
[2 marks]
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(b) Describe why the temperature of the water remains constant at 100°C during boiling, despite continuous heat being supplied by the hot plate. Use the particle model in your answer.
[2 marks]
Show mark scheme
- (a) Particles break free from fixed/rigid positions in the lattice structure OR particles gain enough energy to overcome intermolecular forces
- (a) Particles move more freely with increased random motion OR spacing between particles increases while particles vibrate more
- (b) Heat energy supplied is used to break intermolecular forces/bonds between particles rather than increasing kinetic energy OR energy is used to overcome forces of attraction
- (b) All particles must have sufficient energy to escape from the liquid to become a gas OR the latent heat of vaporisation must be overcome, so temperature stays constant until all liquid has evaporated
GCSE Perfect