Explain why increasing the temperature of a reaction mixture increases the rate of a chemical reaction.

IB DP Chemistry Standard Level (2023 syllabus) — R2.2 How fast? The rate of chemical change · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Increasing the temperature raises the average kinetic energy of the reacting particles, so they move faster. Faster particles collide more often, giving a higher collision frequency. Moreover, a larger fraction of collisions now possess energy equal to or greater than the activation energy. Consequently, the proportion of successful collisions rises, leading to a higher reaction rate.

Examiner tips

  • Use the term "activation energy" and explain that more collisions exceed it.
  • Show the chain: higher KE → more frequent collisions → more successful collisions → higher rate.
  • Keep the answer concise, matching the four points in the mark scheme.

Common mistakes

  • Failing to mention activation energy or the proportion of successful collisions.
  • Using vague terms like "more energy" without linking to activation energy.
  • Writing a long narrative instead of a concise, point‑by‑point explanation.

Mark scheme (4 marks)

  1. Higher temperature means particles have greater average kinetic energy / move faster on average
  2. Particles collide more frequently because they are moving faster
  3. A greater proportion of collisions have energy equal to or greater than the activation energy
  4. Therefore the rate of successful collisions increases, so the rate of reaction increases

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