1. 1
   A pan of ice is heated steadily on a stove. The temperature is monitored and stays constant at 0 degrees Celsius for several minutes while the ice turns to liquid water, even though heating continues throughout.

   (a)

   What is happening to the energy being supplied during this time?

   [1 mark]

   • AThe energy is being used to break the bonds between particles, changing the arrangement of particles from solid to liquid, without increasing their average kinetic energy
   • BThe energy is being reflected away and not absorbed by the ice
   • CThe energy is increasing the average kinetic energy of the particles, raising the temperature
   • DNo energy is being transferred to the ice during this time

   (b)

   What is the name given to the change of state occurring during this constant-temperature stage?

   [1 mark]

   • AMelting
   • BBoiling
   • CEvaporation
   • DCondensation

   (c)

   After all the ice has melted, the temperature of the liquid water begins to rise again as heating continues. Explain, in terms of particles, why the temperature now rises, in contrast to during the melting stage.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A wet swimsuit is hung outside on a warm, windy day and dries out well before the water reaches its boiling point.

   (a)

   Which process is mainly responsible for the swimsuit drying?

   [1 mark]

   • AEvaporation
   • BBoiling
   • CMelting
   • DFreezing

   (b)

   Which factor would NOT increase the rate at which the swimsuit dries?

   [1 mark]

   • APlacing the swimsuit in a sealed plastic bag
   • BIncreasing the air temperature around the swimsuit
   • CIncreasing the wind speed blowing over the swimsuit
   • DSpreading the swimsuit out to increase its exposed surface area

   (c)

   Explain, in terms of particles, why the person wearing the swimsuit as it dries often feels a cooling sensation on their skin.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A laboratory technician is comparing the process of a kettle boiling water with a puddle of rainwater evaporating outside on a mild day.

   (a)

   (a) Describe three differences between boiling and evaporation, referring to where in the liquid each process occurs, the range of temperatures at which each can take place, and whether bubbles are formed.

   [3 marks]

   (b)

   The puddle is spread over a wide, shallow area of pavement on a mild, breezy day, while the kettle is a small, deep, sealed container of water being heated to its boiling point. Explain why the puddle can lose a significant amount of water through evaporation over several hours, even though its temperature never gets close to 100 degrees Celsius, whereas the kettle needs to reach 100 degrees Celsius before losing significant amounts of water as steam.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital sterilises surgical instruments by placing them in boiling water at 100 degrees Celsius for a fixed period of time. A nurse notices that the water in the sterilising unit stays at exactly 100 degrees Celsius throughout the whole boiling process, even though the electric heater beneath the unit continues to supply energy at a constant rate.

   (a)

   Explain fully, in terms of particles and energy, why the temperature of the water does not rise above 100 degrees Celsius while it is boiling, and explain what would need to change for the water to reach a higher temperature.

   [6 marks]

   (b)

   After sterilisation, the nurse removes the instruments and allows the boiling water to cool down and eventually turn to ice in a freezer for storage in a cold room. Explain fully, in terms of particles and energy transfer, the sequence of changes of state that occur as the water cools from steam-producing boiling water down to solid ice, and explain why the temperature remains constant during each change of state but falls steadily between them.

   [6 marks]

   Total for question 4: 12 marks

End of questions