1. 1
   A technician places a small cube of solid wax on a heatproof mat and gently heats it with a Bunsen burner. She records that the wax first melts into a runny liquid, and if heated further it would evaporate into a gas.

   (a)

   Which row correctly describes the arrangement and movement of particles in the solid wax before any heating begins?

   [1 mark]

   • AParticles are held in a fixed, regular arrangement and only vibrate about fixed positions
   • BParticles are close together but arranged randomly, and slide past one another
   • CParticles are far apart and move rapidly in random directions
   • DParticles have no forces of attraction between them and move at constant high speed

   (b)

   The technician continues heating the wax until it turns from a solid directly into a liquid. What is the correct name for this change of state, and is it a physical or chemical change?

   [1 mark]

   • AFreezing; a chemical change
   • BMelting; a chemical change
   • CSublimation; a physical change
   • DMelting; a physical change

   (c)

   Explain, in terms of the arrangement, movement and energy of particles, what happens as the solid wax melts into a liquid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student places an open beaker of ethanol on a windowsill in direct sunlight. Over several hours, the level of liquid in the beaker slowly falls, even though the room temperature stays well below the boiling point of ethanol.

   (a)

   Which term correctly describes this process?

   [1 mark]

   • ABoiling
   • BEvaporation
   • CCondensation
   • DSublimation

   (b)

   The student then covers the beaker with a lid and notices tiny droplets of liquid forming on the underside of the lid. Which statement best explains why these droplets form?

   [1 mark]

   • AEthanol gas particles are compressed by the lid, permanently removing all energy from the particles
   • BEthanol gas particles gain energy near the lid, causing them to bond chemically and form a new liquid substance
   • CEthanol gas particles near the lid lose energy and slow down, allowing forces of attraction to pull them back together into a liquid
   • DEthanol gas particles react with the lid material, producing water droplets as a by-product

   (c)

   The student is told that ethanol has a melting point of -114 degrees Celsius and a boiling point of 78 degrees Celsius. Predict the physical state of ethanol at a room temperature of 20 degrees Celsius, and at a temperature of -150 degrees Celsius. Justify each answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A sealed, rigid metal cylinder contains carbon dioxide gas at room temperature. The cylinder is then placed in a freezer at a very low temperature, and the carbon dioxide inside turns directly into a solid without passing through a liquid state.

   (a)

   Name this change of state, and describe how the arrangement, movement and energy of the carbon dioxide particles change as this occurs.

   [3 marks]

   (b)

   The technician then removes the solid carbon dioxide from the cylinder and leaves it in a warm room, where it disappears directly into a gas without melting into a liquid. Explain this observation in terms of the forces between particles and the energy changes taking place, and name this change of state.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chef removes ice from a freezer and places it in a saucepan of cold water, then heats the pan steadily on a hob until the water boils vigorously and steam rises from the surface. Later, this steam turns back into tiny visible droplets of liquid water in the cooler air just above the pan, and if this cooled water were placed back in the freezer it would eventually solidify again into ice.

   (a)

   A chef pours cold water into a saucepan and heats it steadily on a hob until it boils vigorously, producing steam that rises from the surface. Using ideas about particle arrangement, movement and energy, explain fully what happens to the water as it changes from a solid state of ice (which the chef first removed from a freezer to melt in the pan), through to liquid water, and finally to steam, describing the energy changes and changes in particle behaviour at each stage.

   [6 marks]

   (b)

   The chef notices that as steam rises from the boiling pan, it quickly turns back into tiny visible droplets of liquid water in the cooler air just above the pan, and that if this cooled water were placed back in the freezer it would eventually solidify again into ice. Explain, in terms of energy transfer and particle behaviour, why these interconversions between gas, liquid and solid states happen, and explain why these changes are described as physical changes rather than chemical changes.

   [6 marks]

   Total for question 4: 12 marks

End of questions