Explain how an increase in temperature increases the rate of a chemical reaction, with reference to both collision frequency and activation energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
An increase in temperature raises the average kinetic energy of the reacting particles, so they move faster and collide more often. Consequently, the collision frequency rises. Moreover, a higher temperature shifts the Maxwell–Boltzmann energy distribution to the right, so a larger fraction of collisions possess energy equal to or greater than the activation energy (Ea). Thus, more collisions are successful (meeting both the energy and orientation criteria), which together increases the rate of reaction.
Examiner tips
- Use the terms "collision frequency" and "activation energy" explicitly.
- Show the link between temperature, kinetic energy, and the Maxwell–Boltzmann distribution.
- Explain both the increase in collisions and the increase in successful collisions.
Common mistakes
- Confusing collision frequency with collision energy.
- Forgetting to mention the Maxwell–Boltzmann distribution shift.
- Over‑emphasising orientation while ignoring the energy aspect.
Mark scheme (4 marks)
- An increase in temperature increases the average kinetic energy of particles, so particles move faster and collide more frequently.
- A greater proportion / fraction of collisions have energy equal to or greater than the activation energy (Ea).
- This is because the Maxwell–Boltzmann distribution shifts to higher energies at higher temperature, so the area under the curve beyond Ea is larger.
- The combined effect of increased collision frequency and a greater proportion of successful collisions (those meeting both the energy and orientation requirements) results in a significantly increased rate of reaction.
Key terms in this question
activation energy · collision frequency
Related
- All IB DP Chemistry Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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