GCSE Combined Science (AQA)

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Chemistry subject content Energy changes

Activation Energy

3:00 Exothermic and endothermic reactions
Spec 5.5.1
  • Chemical reactions occur when reacting particles collide.
  • Particles must collide with sufficient energy for a reaction to occur.
  • Without sufficient energy, particles bounce off each other, and no reaction happens.
  • The minimum energy needed for a reaction is called activation energy.
  • Heating reactants can provide the necessary energy to reach activation energy.
  • Reactions vary in activation energy; some occur at room temperature, others require additional energy.
  • All reactions, including exothermic ones, have an activation energy.
  • Exothermic reactions release energy to the surroundings but still require initial activation energy.
  • A bunsen burner is an example where initial energy is needed to start a reaction, which then releases more energy.

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