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AQASpec 4.5Foundation & Higher~25 min

Energy Changes

Chemistry · Topic revision workspace

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Read the notes, score 80% and know 75% of the cards.

Topic overview

What you need to know

Energy Changes is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. A reaction that transfers energy to the surroundings, causing the temperature to rise. E.g. combustion, neutralisation. A reaction that takes in energy from the surroundings, causing the temperature to fall. E.g. thermal decomposition, photosynthesis. The minimum amount of energy needed for a reaction to occur. Represented by the initial rise on an energy profile diagram.

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

  • Exothermic Reaction: A reaction that transfers energy to the surroundings, causing the temperature to rise. E.g. combustion, neutralisation.
  • Endothermic Reaction: A reaction that takes in energy from the surroundings, causing the temperature to fall. E.g. thermal decomposition, photosynthesis.
  • Activation Energy: The minimum amount of energy needed for a reaction to occur. Represented by the initial rise on an energy profile diagram.
  • Bond Breaking: Breaking bonds is an endothermic process — it requires energy input.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

  • Bond Making: Making bonds is an exothermic process — it releases energy.
  • Energy Profile Diagram: A diagram showing the energy levels of reactants and products. If products are lower, the reaction is exothermic; higher = endothermic.
  • Catalyst: A substance that speeds up a reaction without being used up. It provides an alternative pathway with lower activation energy.
  • Reaction Profile (Overall Energy Change): If energy released in bond making > energy used in bond breaking, the reaction is exothermic (and vice versa).

Core knowledge

Key facts for Energy Changes

1

Exothermic Reaction

A reaction that transfers energy to the surroundings, causing the temperature to rise. E.g. combustion, neutralisation.

2

Endothermic Reaction

A reaction that takes in energy from the surroundings, causing the temperature to fall. E.g. thermal decomposition, photosynthesis.

3

Activation Energy

The minimum amount of energy needed for a reaction to occur. Represented by the initial rise on an energy profile diagram.

4

Bond Breaking

Breaking bonds is an endothermic process — it requires energy input.

5

Bond Making

Making bonds is an exothermic process — it releases energy.

6

Energy Profile Diagram

A diagram showing the energy levels of reactants and products. If products are lower, the reaction is exothermic; higher = endothermic.

7

Catalyst

A substance that speeds up a reaction without being used up. It provides an alternative pathway with lower activation energy.

8

Reaction Profile (Overall Energy Change)

If energy released in bond making > energy used in bond breaking, the reaction is exothermic (and vice versa).

Active recall

Close the notes and answer these

  1. 1.Without looking, explain exothermic reaction and give one example or consequence.
  2. 2.Without looking, explain endothermic reaction and give one example or consequence.
  3. 3.Without looking, explain activation energy and give one example or consequence.
  4. 4.Without looking, explain bond breaking and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

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