Changing the pressure on the reaction
3 marks · NormalExplain, using particle theory, why changing the pressure has little effect on the rate of reactions involving only liquids.
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Particles in liquids are already close together with little space between them. Increasing the pressure does not bring the particles significantly closer, so it does not increase the frequency of collisions. Therefore, the rate of reaction changes very little.
Also accept: Liquid particles are already packed together so pressure doesn't make much difference; There is little space for particles to move, so collisions do not increase
Common mistakes: Saying liquids behave like gases; Ignoring particle arrangement
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Marking points
M1 · 1 mark · Mentions liquid particles are closely packed or little space between them.
M2 · 1 mark · States that increasing pressure does not significantly decrease the space between particles or bring them closer together.
M3 · 1 mark · Concludes or explains that collision frequency does not increase, so there is little or no effect on rate.
Worked solution
Liquids have particles that are already closely packed, with very little space between them. Increasing the pressure does not make them significantly closer, so the number of collisions per second does not increase. Therefore, increasing the pressure has little effect on the rate of reaction for liquids.