Changing the pressure on the reaction
2 marks · HardA reaction takes place between two gases. The pressure is increased by decreasing the volume of the container.
Explain why this leads to a faster reaction rate, using ideas about particle collisions.
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Also accept: Particles are packed closely; collide more often per second; more frequent successful collisions
Common mistakes: Only stating 'rate increases' with no collision explanation; Suggesting pressure has no effect for gases
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Marking points
B1 · 1 mark · States that gas particles are closer together/collisions become more frequent.
B2 · 1 mark · Links more frequent collisions to an increase in the rate of reaction.
Worked solution
When the pressure is increased by reducing the volume, gas particles are forced closer together.
This makes collisions between particles more frequent, which causes the reaction rate to increase.