Energy transfer during exothermic and endothermic reactions - AQA GCSE Chemistry Exam Questions

Practise 30 exam-style questions on Energy transfer during exothermic and endothermic reactions for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

30 questions
1–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

A student mixed two solutions. The temperature of the mixture fell from 21 °C to 15 °C.

State whether the reaction is exothermic or endothermic. Give a reason for your answer.

Model answer

The reaction is endothermic, because the temperature decreased, showing that energy was taken in from the surroundings.

Explanation

You can tell exothermic and endothermic reactions apart from the temperature change of the surroundings. A fall in temperature means energy has been taken in by the reaction.

Mark scheme

1 mark
endothermic
1 mark
the temperature decreased, so energy was taken in from the surroundings
allow the temperature went down

Question 2

3 marks

Some sports injury packs contain chemicals that undergo an endothermic process when the pack is squeezed.

Explain how the pack can be used to treat an injury.

Model answer

When the pack is squeezed, an endothermic process starts that takes in energy from the surroundings, including the injured part of the body. This lowers the temperature of the injured area, which helps to reduce the swelling and pain.

Explanation

An endothermic change takes energy from whatever is around it, so the pack and the skin it touches get colder. This works like an ice pack but can be carried at room temperature and activated when needed.

Mark scheme

1 mark
the pack takes in energy from its surroundings
allow from the injured area / skin
1 mark
so the temperature (of the pack and the area it touches) decreases
allow the pack feels cold
1 mark
this cools the injury / reduces swelling or pain

Question 3

3 marks

In an endothermic reaction, the products have more energy than the reactants.

Explain where this extra energy comes from and why the temperature of the solution falls.

Model answer

The extra energy stored in the products is taken in from the surroundings, which includes the water in the solution, the container and the air. Because the surroundings lose energy, their temperature decreases, so the thermometer in the solution shows a fall in temperature.

Explanation

Energy is conserved, so the energy gained by the products must have come from somewhere. In a solution, the water counts as part of the surroundings, which is why it gets colder.

Mark scheme

1 mark
the energy is taken in from the surroundings
allow from the water / solution / container / air
1 mark
the surroundings lose energy
1 mark
so the temperature of the surroundings (the solution) decreases

Question 4

4 marks

When methane burns in oxygen, energy is transferred to the surroundings.
CH₄ + 2O₂ → CO₂ + 2H₂O

Explain what this shows about the energy of the products compared with the reactants, and how this is consistent with the conservation of energy.

Model answer

Burning methane is exothermic. Because energy is transferred to the surroundings, the products, carbon dioxide and water, must have less energy than the reactants, methane and oxygen. The difference in energy is exactly the amount transferred to the surroundings. No energy is created or destroyed: the energy lost by the chemicals is gained by the surroundings, so the total energy of the universe stays the same.

Explanation

Conservation of energy means any energy given out must have come from the substances. That is why the products of an exothermic reaction have less energy than the reactants, by the amount transferred.

Mark scheme

1 mark
the reaction is exothermic
1 mark
the products (carbon dioxide and water) have less energy than the reactants (methane and oxygen)
1 mark
the difference is equal to the energy transferred to the surroundings
1 mark
energy is not created or destroyed, so the total energy (of the universe) is the same before and after the reaction

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