1. 1
   A self-heating camping meal pouch contains calcium oxide, which reacts with water in a separate compartment to warm the food when the pouch is activated. Hikers use these pouches to enjoy a hot meal without needing a stove.

   (a)

   The temperature of the surroundings increases as the reaction proceeds. What type of reaction is this?

   [1 mark]

   • AEndothermic
   • BExothermic
   • CReversible only
   • DNeutral, with no energy transfer

   (b)

   Which of the following is another everyday example of the same type of reaction as the one heating the camping meal?

   [1 mark]

   • ACombustion of fuel in a campfire
   • BThe thermal decomposition of a metal carbonate on heating
   • CThe reaction of citric acid with sodium hydrogencarbonate in a cold pack
   • DA reversible reaction reaching equilibrium

   (c)

   Explain, in terms of energy transfer, why the reaction between calcium oxide and water heats up the food in the pouch.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A sports physiotherapist activates an instant cold pack, containing ammonium nitrate and water, to treat a player's sprained ankle straight after the injury occurs on the pitch.

   (a)

   The temperature of the pack decreases noticeably as the reaction proceeds. What type of reaction is taking place inside the pack?

   [1 mark]

   • AExothermic
   • BNeutralisation only
   • CCombustion
   • DEndothermic

   (b)

   Which of the following is another example of the same type of reaction as the one in the cold pack?

   [1 mark]

   • ACombustion of a fuel
   • BA metal reacting with oxygen
   • CThermal decomposition of a metal carbonate on heating
   • DNeutralisation of an acid with an alkali

   (c)

   Explain, in terms of energy transfer, why the cold pack feels cold to the touch after it has been activated.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An 18th century chemist, in the style of early calorimetry experiments, measures the temperature change when two chemicals react in an insulated container and draws a reaction profile (energy level diagram) for the reaction, in order to understand the energy changes taking place.

   (a)

   Describe what a reaction profile shows, including the significance of the activation energy on the diagram.

   [3 marks]

   (b)

   The chemist notices that not every collision between reacting particles results in a reaction. Using collision theory, explain why this is the case, and describe how increasing the temperature of the reaction mixture would affect the rate of successful collisions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A product design team is developing a new commercial hand warmer based on the reaction between hydrogen and chlorine gas, H2 + Cl2 -> 2HCl, and needs to confirm the reaction is exothermic and assess whether it would be a safe choice for a consumer product.

   (a)

   Using the bond energies provided (H-H = 436 kJ/mol, Cl-Cl = 243 kJ/mol, H-Cl = 432 kJ/mol), calculate the overall energy change for this reaction and state whether it is exothermic or endothermic.

   [6 marks]

   (b)

   Evaluate whether the reaction between hydrogen and chlorine would actually be a suitable and safe choice for a commercial hand warmer, and suggest one alternative exothermic reaction that manufacturers commonly use instead, giving reasons for your choice.

   [6 marks]

   Total for question 4: 12 marks

End of questions