Changing the pressure on the reaction
2 marks · NormalState what happens to the rate of a reaction involving gases when the pressure is increased. Briefly explain your answer.
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The rate of reaction increases. Increasing pressure causes gas particles to collide more frequently.
Also accept: It increases because there are more frequent collisions between gas particles.; Rate increases because particles are closer together and collide more often.; The reaction speeds up due to more particle collisions.
Common mistakes: Saying only that rate increases, with no explanation.; Confusing with temperature effect.
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Marking points
B1 · 1 mark · States that the rate of reaction increases when pressure is increased (for gases).
B2 · 1 mark · Explains that this is because gas particles collide more frequently when pressure increases.
Worked solution
The rate of a reaction involving gases increases when the pressure is increased because the gas particles are squeezed closer together, so they collide more frequently.