RevTree
Back to skills
#109

Rates of reaction (overview)

Paper 2 · Higher combined

Key steps (method)

  • Translate the question into: rate = change ÷ time.
  • Pick the right measurement method: mass loss or gas volume (or precipitation / colour change).
  • Use a graph carefully: rate = gradient (tangent for instantaneous rate).
  • Link ideas to collision theory: more frequent + more energetic collisions.

Common mistakes

  • Using the wrong time units (s vs min) or wrong volume units (cm³ vs dm³).
  • Reading graphs incorrectly (average vs instantaneous rate).
  • Saying catalysts “increase energy” (they lower activation energy).

Exam-style questions (quick)

  1. A gas volume increases by 36 cm³ in 90 s. Calculate the average rate.
  2. State two ways to increase the rate of reaction and explain using collision theory.
  3. Explain how a catalyst changes the reaction profile.