1. 1
   A student adds a spatula of solid sodium hydroxide to a test tube of water and measures the temperature before and after. The temperature rises from 20°C to 34°C within a few seconds.

   (a)

   A student adds a spatula of solid sodium hydroxide to water in a test tube and notices the tube becomes noticeably warmer to the touch. What type of reaction is this?

   [1 mark]

   • AEndothermic, because energy is taken in from the surroundings
   • BExothermic, because energy is transferred to the surroundings
   • CEndothermic, because energy is transferred to the surroundings
   • DNeither exothermic nor endothermic, because no new substance is formed

   (b)

   Which sign convention for $\Delta H$ would be used to describe this reaction?

   [1 mark]

   • ANegative $\Delta H$
   • BPositive $\Delta H$
   • CZero $\Delta H$
   • D$\Delta H$ cannot be determined without a catalyst

   (c)

   Explain, in terms of energy transfer, why the temperature of the water increases when sodium hydroxide dissolves, and name one other type of reaction that is typically exothermic.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student heats solid copper carbonate strongly in a test tube using a Bunsen burner. The green solid gradually turns black, and the reaction stops progressing whenever the Bunsen burner flame is removed.

   (a)

   What type of reaction is this?

   [1 mark]

   • AExothermic, because energy is transferred to the surroundings
   • BEndothermic, because energy is transferred to the surroundings
   • CExothermic, because energy is taken in from the surroundings
   • DEndothermic, because energy is taken in from the surroundings

   (b)

   What sign convention for $\Delta H$ describes this thermal decomposition reaction?

   [1 mark]

   • ANegative $\Delta H$
   • B$\Delta H$ equal to zero
   • CPositive $\Delta H$
   • D$\Delta H$ cannot have a sign for solid reactants

   (c)

   Explain why this reaction stops when the Bunsen burner is removed, and state the name given to this type of reaction where a compound breaks down on heating.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A first-aid instructor demonstrates a sports injury cold pack, which contains a solid chemical and a sealed pouch of water inside an outer plastic bag. When squeezed, the inner pouch bursts, allowing the solid to dissolve in the water, and the whole pack quickly becomes cold to the touch.

   (a)

   Sports injury cold packs contain a solid and a separate pouch of water. When the pack is squeezed, the pouch breaks and the solid dissolves, and the pack becomes noticeably cold. Explain, in terms of energy transfer, why the pack becomes cold, and state the sign of $\Delta H$ for this process.

   [3 marks]

   (b)

   Explain why cold packs are useful for treating sports injuries, and suggest, giving a reason, what type of chemical process might be used instead if a manufacturer wanted to design a pack that becomes hot rather than cold.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A food packaging company is developing a self-heating food can that uses a chemical reaction inside its base, separate from the food itself, to warm the contents without an external flame or electricity.

   (a)

   A fuel company is comparing several reactions to decide which could be used in a self-heating food can, where an exothermic reaction inside the base of the can heats the food without any external flame. Explain what is meant by an exothermic reaction, describe how a manufacturer could experimentally confirm that a candidate reaction is exothermic, and discuss why exothermic reactions such as combustion and neutralisation would be suitable choices.

   [6 marks]

   (b)

   Explain what is meant by an endothermic reaction, and discuss why an endothermic reaction would NOT be a suitable choice for the self-heating can described above, using the definitions and sign convention of $\Delta H$ to support your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions