Suggest — 3 marks
A student is investigating different chemical reactions. They observe that when calcium oxide reacts with water, the container becomes very hot. When ammonium nitrate dissolves in water, the container becomes very cold.
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(a) Suggest which reaction is exothermic. Explain your answer.
[1 mark]
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(b) Suggest why the ammonium nitrate reaction would be unsuitable for hand warmers used by hikers.
[1 mark]
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(c) Suggest two practical uses for the calcium oxide and water reaction based on the energy change that occurs.
[1 mark]
Show mark scheme
- (a) Award 1 mark for: calcium oxide and water reaction (or naming it as exothermic because the container becomes hot / releases heat energy)
- (b) Award 1 mark for: it absorbs heat / cools down / is endothermic (so would make hands colder, not warmer) OR it would remove heat from the body
- (c) Award 1 mark for any two from: heating water / providing hot water; sterilisation / killing bacteria; hand warmers / heat packs; cooking food; industrial heating processes
Explain — 4 marks
A student is investigating two different chemical reactions in the laboratory. Reaction A involves mixing calcium oxide with water, and the test tube becomes too hot to hold. Reaction B involves dissolving ammonium nitrate in water, and the test tube becomes cold enough to form ice on the outside.
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(a) Explain why the test tube becomes hot during Reaction A.
[1 mark]
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(b) Explain why the test tube becomes cold during Reaction B.
[1 mark]
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(c) Explain the difference between exothermic and endothermic reactions in terms of energy transfer.
[2 marks]
Show mark scheme
- (a) Reaction A is exothermic / releases energy to the surroundings
- (b) Reaction B is endothermic / absorbs energy from the surroundings
- (c) Exothermic reactions transfer/release energy to the surroundings (causing temperature increase)
- (c) Endothermic reactions take in/absorb energy from the surroundings (causing temperature decrease)
Evaluate — 3 marks
A student is designing a hand warmer product for use during winter. They are considering two options: Option A uses a chemical reaction that releases heat to the surroundings, while Option B uses a chemical reaction that absorbs heat from the surroundings. The student needs to decide which type of reaction would be more suitable for their hand warmer.
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(a) Identify which type of chemical reaction (exothermic or endothermic) would be suitable for a hand warmer product and explain your choice.
[2 marks]
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(b) Evaluate why the unsuitable reaction type would not work effectively for keeping hands warm.
[1 mark]
Show mark scheme
- (a) Identifies exothermic reaction as suitable for hand warmer
- (b) Explains that exothermic reactions release/give out heat to the surroundings, which would warm the hands
- (b) Evaluates that endothermic reactions absorb heat from surroundings, which would cool the hands rather than warm them / would be ineffective as it removes thermal energy
Explain — 2 marks
A student is investigating two reactions. Reaction A is used in instant ice packs sold for sports injuries, while Reaction B is used in self-heating coffee cups. Both reactions involve dissolving a solid in water.
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(a) Reaction A causes the temperature of the water to decrease. Explain why this happens in terms of energy transfer.
[1 mark]
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(b) Explain the difference between the energy changes that occur in Reaction A and Reaction B.
[1 mark]
Show mark scheme
- (a) Energy is taken in/absorbed from the surroundings / the reaction requires energy to break bonds (1 mark)
- (b) Reaction A is endothermic (takes in energy) while Reaction B is exothermic (releases energy) / Reaction A requires more energy to break bonds than is released when new bonds form, whereas Reaction B releases more energy when new bonds form than is required to break bonds (1 mark)
Calculate — 2 marks
A student investigates the heat released when magnesium ribbon reacts with dilute hydrochloric acid. The student records the temperature of the acid before and after adding the magnesium.
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(a) The initial temperature of the acid was 21°C. The final temperature was 45°C. Calculate the temperature change.
[1 mark]
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(b) The student repeats the experiment three times and records temperature changes of 22°C, 26°C and 24°C. Calculate the mean temperature change.
[1 mark]
Show mark scheme
GCSE Perfect