Changing the pressure on the reaction
5 marks · HardA student investigates the effect of pressure on two reactions:
Reaction 1: Two solid powders are mixed together in a sealed container. Predict what happens to the rate of reaction if the pressure is increased. Explain your answer using particle theory.
Reaction 2: Two liquids are mixed together. Explain, using your knowledge of particle arrangement, why increasing the pressure has little effect on the rate of reaction.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) —
(b) —
Common mistakes: Suggesting significant effect for solids or liquids; not mentioning particle arrangement
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Predicts there is little or no effect on the rate for solids.
B2 (a) · 1 mark · States that solid particles are already packed closely together.
B3 (a) · 1 mark · Explains that increasing pressure does not significantly change the volume or the distance between solid particles, so collision frequency doesn't change.
B4 (b) · 1 mark · States that changing the pressure has little effect on the rate for liquids.
B5 (b) · 1 mark · Explains that liquid particles are already very close together, so little or no change occurs in collision frequency with increased pressure.
Worked solution
a) For the reaction between two solids, increasing the pressure has little or no effect on the rate.
This is because solid particles are already packed closely together, so increasing pressure does not make them significantly closer or increase the number of collisions.
b) For the reaction between two liquids, increasing the pressure also has little effect on the reaction rate.
This is because liquid particles are already very close together, and squeezing them makes almost no difference to their arrangement or collision frequency.