1. 1
   A foundry technician heats scrap aluminium in a furnace until it melts completely so it can be recast into engine parts.

   (a)

   Which statement correctly compares the arrangement and movement of particles in the molten (liquid) aluminium with the solid aluminium before heating?

   [1 mark]

   • AIn the liquid, particles are further apart on average and can move past one another, whereas in the solid they vibrate about fixed positions
   • BIn the liquid, particles are closer together than in the solid and are held in a fixed regular arrangement
   • CIn the liquid, particles no longer attract one another at all, whereas in the solid strong attractive forces hold them together
   • DIn the liquid, particles move only in straight lines between rare collisions, whereas in the solid they do not move at all

   (b)

   While the aluminium is melting, the furnace continues to supply energy at a constant rate, but a thermometer reading shows the temperature of the aluminium stays constant during the melting process. Which statement explains this observation?

   [1 mark]

   • AThe furnace automatically reduces its power output once melting begins
   • BThe energy supplied is used to break the bonds between particles rather than to increase their average kinetic energy
   • CThe aluminium reflects all of the energy supplied to it once it reaches its melting point
   • DThe particles stop moving completely during the change of state

   (c)

   Explain, in terms of the particles of the aluminium, why the temperature does not rise while the metal is melting even though the furnace continues to supply energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A camper uses a gas stove to heat 0.5 kg of water in a metal kettle in order to make hot drinks.

   (a)

   Which quantity is defined as the energy required to raise the temperature of one kilogram of a substance by one degree Celsius?

   [1 mark]

   • AThermal conductivity
   • BSpecific latent heat of fusion
   • CSpecific latent heat of vaporisation
   • DSpecific heat capacity

   (b)

   The camper continues heating the water after it starts to boil, turning some of it into steam. Which statement correctly compares the energy needed to boil away 0.5 kg of water at 100°C with the energy needed to heat the same 0.5 kg of water from 20°C to 100°C?

   [1 mark]

   • ABoth processes require exactly the same amount of energy
   • BBoiling away the water requires considerably less energy than heating it from 20°C to 100°C
   • CBoiling away the water requires considerably more energy than heating it from 20°C to 100°C
   • DBoiling away the water requires no additional energy once it has reached 100°C

   (c)

   The specific heat capacity of water is 4200 J/kg°C. Calculate the energy required to heat the 0.5 kg of water from 20°C to 100°C. State the equation you use.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the cooling curve of molten stearic acid by heating a test tube of stearic acid until it is fully liquid, then leaving it to cool while recording its temperature every thirty seconds.

   (a)

   Describe the shape of the temperature–time graph the student would expect to obtain as the stearic acid cools from liquid to solid, referring to what happens to the particles at each stage.

   [3 marks]

   (b)

   A second student repeats the experiment using a sample of stearic acid that has been contaminated with a small amount of a different wax. Explain how the presence of this impurity would affect the melting/freezing point shown on the cooling curve, and describe one change to the experimental procedure that would improve the reliability of the results.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A physiotherapist recommends two treatments for a sports injury: Pack X contains 0.2 kg of ice at 0°C that is allowed to melt completely against the skin, and Pack Y contains 0.2 kg of water at 0°C that simply warms up.

   (a)

   Using kinetic theory and the concept of specific latent heat of fusion, explain why Pack X is able to absorb more energy from the injured area than Pack Y over the same rise to body temperature, and explain why this makes Pack X more effective at keeping the injury cool for longer.

   [6 marks]

   (b)

   The specific latent heat of fusion of ice is 334000 J/kg. Calculate the energy absorbed as the 0.2 kg of ice in Pack X melts completely, showing your working. Then explain, using kinetic theory, why the temperature of the melted water does not begin to rise until melting is fully complete.

   [6 marks]

   Total for question 4: 12 marks

End of questions