1. 1
   An engineer heats a 3 kg aluminium engine block from 20 C to 90 C using an electric heating element, to test its thermal properties before machining.

   (a)

   What does it mean for aluminium to have a specific heat capacity of 900 J/(kg C)?

   [1 mark]

   • A900 J of energy is needed to melt 1 kg of aluminium
   • B900 J of energy is needed to raise the temperature of 1 kg of aluminium by 1 C
   • C900 J of energy is released when 1 kg of aluminium cools by 1 C only
   • D900 J is the total energy stored in 1 kg of aluminium

   (b)

   As the aluminium block is heated from 20 C to 90 C but remains solid throughout, what happens to its particles according to kinetic theory?

   [1 mark]

   • AThe particles gain kinetic energy and vibrate more about fixed positions
   • BThe particles gain kinetic energy and move freely past one another
   • CThe particles lose kinetic energy as the block heats up
   • DThe particles spread apart to fill the container

   (c)

   Calculate the energy needed to heat the 3 kg aluminium block from 20 C to 90 C, given its specific heat capacity is 900 J/(kg C).

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist heats 0.4 kg of solid naphthalene wax in a water bath until it completely melts at its melting point, without changing its temperature during the melting process.

   (a)

   What does the specific latent heat of fusion of a substance represent?

   [1 mark]

   • AThe energy needed to raise the temperature of 1 kg of the substance by 1 C
   • BThe energy needed to change the state of 1 kg of the substance from solid to liquid at constant temperature
   • CThe energy released when 1 kg of the substance freezes
   • DThe energy needed to change 1 kg of the substance from liquid to gas

   (b)

   While the wax is melting, its temperature does not change even though energy is continually supplied. Which statement best explains this?

   [1 mark]

   • ANo energy is being transferred to the wax during melting
   • BThe energy supplied is being lost to the surroundings, not to the wax
   • CThe wax's specific heat capacity becomes zero during melting
   • DThe energy supplied increases the potential energy between particles, breaking bonds, rather than increasing their kinetic energy

   (c)

   Calculate the energy needed to melt the 0.4 kg of wax, given its specific latent heat of fusion is 150000 J/kg.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metallurgist compares two samples of tin: one pure, and one containing a small amount of lead as an impurity. Each sample is heated steadily from solid and its temperature is recorded at regular time intervals until it is fully liquid.

   (a)

   State the effect that the lead impurity has on the melting point of the tin sample compared with the pure tin, and describe, in words, what happens to the temperature of the pure tin sample while it is melting.

   [3 marks]

   (b)

   Describe, in words, the shape of a temperature-time graph for the pure tin sample as it is heated steadily from solid at room temperature until it is fully liquid and continuing to heat, and explain, using the particle model, why the temperature is constant during the plateau.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A laboratory kettle heats 0.5 kg of water that is already at its boiling point of 100 C, converting it entirely into steam at 100 C. Separately, a technician leaves an open dish containing the same mass of water at room temperature on a lab bench overnight, where it slowly evaporates.

   (a)

   Calculate the energy needed to convert the 0.5 kg of boiling water entirely into steam at 100 C, and explain why this energy does not raise the temperature of the water above 100 C.

   [6 marks]

   (b)

   Explain, using kinetic theory, how the water in the open dish can evaporate overnight even though it never reaches 100 C, and describe two factors that would increase the rate at which it evaporates.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A cook compares two saucepan handles of identical size and shape, one made of solid steel and one made of solid wood, while the pan sits on a hot stove.

   (a)

   Which statement correctly explains why the steel handle conducts heat much better than the wooden handle?

   [1 mark]

   • ASteel has free electrons that transfer energy quickly through the metal by colliding with other particles
   • BWood contains free electrons that trap heat
   • CSteel is a poor conductor because it has no free electrons
   • DWood conducts heat well because it is a solid

   (b)

   In both the steel and the wooden handle, energy is also transferred to some extent by particle vibrations and collisions. Which statement describes this process of conduction?

   [1 mark]

   • AParticles that gain kinetic energy near the hot end vibrate more and collide with neighbouring particles, passing on energy
   • BParticles physically move from the hot end to the cold end carrying energy with them
   • CEnergy is transferred only by electromagnetic waves through the solid
   • DConduction requires the material to be a liquid or gas

   (c)

   Suggest why a wooden handle, despite being a worse conductor of heat, might be preferred for a saucepan that will be picked up by hand.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A greenhouse gardener notices that on a sunny day, warm air rises from the black-painted concrete floor of the greenhouse to the roof, while cooler air near the roof vents sinks back down to floor level, setting up a continuous circulation of air within the greenhouse.

   (a)

   Which statement correctly explains why the warm air near the greenhouse floor rises?

   [1 mark]

   • AThe warm air's particles move further apart, making it less dense than the surrounding cooler air, so it rises
   • BThe warm air's particles move closer together, making it denser, so it rises
   • CWarm air always rises because it contains more particles than cool air
   • DWarm air rises because gravity pulls cooler air down first, leaving a gap

   (b)

   What name is given to this circulation of warm and cool air within the greenhouse?

   [1 mark]

   • AConduction
   • BRadiation
   • CConvection
   • DEvaporation

   (c)

   Explain what happens to the air as it rises to the roof, cools, and then sinks back down, to complete the circulation described.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   An engineer is designing a heat sink for a computer processor. She is deciding between a heat sink made from aluminium with a matt black finish and many thin cooling fins, and a smaller, smooth, shiny steel block of the same total mass.

   (a)

   State three factors that affect the rate at which the heat sink transfers energy away from the processor by heating the surroundings.

   [3 marks]

   (b)

   Explain why the finned, matt black aluminium heat sink is likely to transfer energy away from the processor faster than the smooth, shiny steel block of the same mass.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Civil engineers fit expansion gaps between sections of a long steel pedestrian bridge, and also build a nearby section of railway track using continuous welded rail with no traditional expansion gaps, relying instead on the rail being pre-stressed and clamped tightly to its concrete sleepers.

   (a)

   Explain, using the particle model, why the steel sections of the bridge expand on a hot day, and explain why the engineers leave expansion gaps between the sections.

   [6 marks]

   (b)

   The nearby railway track uses continuous welded rail with no expansion gaps, relying instead on the rail being pre-stressed and firmly clamped to its sleepers. Explain how this alternative approach controls the effects of thermal expansion, and describe one hazard that could occur on a very hot day if a section of rail were not properly clamped.

   [6 marks]

   Total for question 8: 12 marks

End of questions