A student investigates the effect of temperature on the rate of a reaction between hydrochloric acid and sodium thiosulfate solution. As temperature increases, the rate of reaction increases. Explain why increasing temperature causes the rate of reaction to increase.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When sodium thiosulfate solution reacts with hydrochloric acid, a yellow precipitate of sulfur is produced. The student measures the time taken for a fixed amount of sulfur to form at different temperatures.
Model answer (5 marks)
Increasing temperature raises the kinetic energy of the reactant particles.
Higher kinetic energy means particles move faster and collide more often.
With more frequent collisions, a larger proportion of them possess energy equal to or greater than the activation energy.
These high‑energy collisions are more likely to be successful, leading to product formation.
Consequently, the overall rate of the reaction increases as temperature rises.
Higher kinetic energy means particles move faster and collide more often.
With more frequent collisions, a larger proportion of them possess energy equal to or greater than the activation energy.
These high‑energy collisions are more likely to be successful, leading to product formation.
Consequently, the overall rate of the reaction increases as temperature rises.
Examiner tips
- Use the kinetic‑molecular theory terms (kinetic energy, collision frequency, activation energy).
- Show the logical chain: temperature → kinetic energy → collision frequency & energy distribution → successful collisions → rate increase.
Common mistakes
- Confusing temperature with concentration; stating only ‘more collisions’ without linking to activation energy.
- Using vague phrases like ‘particles move faster’ without mentioning kinetic energy or activation energy.
Mark scheme (5 marks)
- Increasing temperature increases the kinetic energy of the particles
- Particles collide more frequently / more often
- A greater proportion / more particles have energy greater than or equal to the activation energy
- Therefore more collisions are successful / result in a reaction
- So the rate of reaction increases (linked to the explanation above)
Key terms in this question
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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