1. 1
   A camping enthusiast burns a small gas fuel cartridge in a portable stove to heat a pan of water, then later dissolves a cold-pack chemical sachet in water to treat a minor injury, and wants to understand the different heat energy changes taking place.

   (a)

   A camping enthusiast burns a fuel cartridge to heat water for cooking and notices that the surroundings become warmer as the reaction proceeds. What type of reaction is combustion classified as, in terms of energy transfer?

   [1 mark]

   • AEndothermic
   • BExothermic
   • CNeither exothermic nor endothermic
   • DPhotochemical

   (b)

   The camper then uses a first-aid cold pack, which contains a chemical that dissolves in water and makes the pack feel noticeably colder. What type of process is this dissolving classified as, in terms of energy transfer?

   [1 mark]

   • AExothermic
   • BCombustion
   • CEndothermic
   • DNeutralisation

   (c)

   Describe a simple calorimetry experiment the camper could carry out at home to measure the temperature change when the cold-pack chemical dissolves in water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer at a company that manufactures hand-warmers and instant cold-packs is testing the heat energy changes of a new exothermic displacement reaction hand-warmer design, using calorimetry and energy level diagrams to model the reaction before mass production.

   (a)

   An engineer tests a new industrial hand-warmer that undergoes an exothermic displacement reaction when activated. On an energy level diagram for this reaction, how do the energy levels of the products compare with the energy level of the reactants?

   [1 mark]

   • AProducts are higher in energy than reactants
   • BEnergy level cannot be shown on a diagram for this reaction
   • CProducts and reactants have identical energy
   • DProducts are lower in energy than reactants

   (b)

   The engineer measures a temperature rise of 12°C when 50 g of water in the hand-warmer reacts, using the specific heat capacity of water, c = 4.2 J/g°C. Using Q = mcT, which expression correctly calculates the heat energy released, Q?

   [1 mark]

   • AQ = 50 × 4.2 × 12
   • BQ = 50 + 4.2 + 12
   • CQ = 50 ÷ 4.2 ÷ 12
   • DQ = 50 × 4.2 ÷ 12

   (c)

   Sketch in words (describe) the shape of an energy level diagram for the hand-warmer's exothermic reaction, labelling where the activation energy and the overall enthalpy change (ΔH) would appear.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A power station engineer is investigating the energy released when methane gas is burned to generate electricity, and wants to use bond energy data to calculate and explain the overall enthalpy change of the combustion reaction before optimising the power station's fuel efficiency.

   (a)

   A power station engineer is analysing the combustion of methane gas to understand why so much heat energy is released. Explain, in terms of bond breaking and bond making, why the combustion of methane is an overall exothermic process.

   [3 marks]

   (b)

   Using the bond energies below, calculate the overall enthalpy change, ΔH, for the complete combustion of methane: CH4 + 2O2 → CO2 + 2H2O. Bond energies: C–H = 413 kJ/mol, O=O = 498 kJ/mol, C=O = 799 kJ/mol, O–H = 463 kJ/mol. (Methane has 4 C–H bonds, oxygen has 2 O=O bonds, carbon dioxide has 2 C=O bonds, water has 2 O–H bonds per molecule and there are 2 water molecules.)

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A university research student is carrying out an investigation into the enthalpy change of neutralisation between hydrochloric acid and sodium hydroxide solution, using simple calorimetry, as part of a wider project comparing the enthalpy changes of several different acid-base neutralisation reactions.

   (a)

   A university research student is investigating the enthalpy change of neutralisation between hydrochloric acid and sodium hydroxide solution using simple calorimetry. Describe, in full detail, how the student could carry out the experiment to determine the temperature change of the reaction, and explain how the heat energy change (Q) and molar enthalpy change (ΔH) could then be calculated from the results.

   [6 marks]

   (b)

   The research student repeats the neutralisation experiment several times and notices that the calculated enthalpy change of neutralisation is consistently lower in magnitude (less negative) than the accepted literature value. Evaluate possible reasons for this discrepancy and suggest improvements the student could make to obtain a more accurate result.

   [6 marks]

   Total for question 4: 12 marks

End of questions