2021 P1 Q12 - Deduce Change in Rate of Forward Reaction when POE shifts

Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 12.

2021 p1 q12 question

We need to deduce the change in the rate of forward reaction during this pressure change.

Let's break this down into 2 parts.

1. Deduce POE and rate of forward reaction at time t

At time t, the partial pressure of CO2 is lowered.

According to Le Chatelier's Principle, position of equilibrium will shift to the left to form more reactant CO2 and increase its partial pressure to counter the change imposed.

2021 p1 q12 POE shift left

The reverse reaction is favoured and forward reaction is disfavoured.

Hence rate of forward reaction will decrease.

We can eliminate options C and D since there is no decrease in rate of forward reaction.

2021 p1 q12 eliminate option

Check out the following video lesson to learn more about Le Chatelier's Principle and other changes that affect the position of equilibrium.

2. Deduce rate after return to atmospheric pressure

The pressure returns to original atmospheric pressure at constant temperature.

This means that the final state will have the same temperature and pressure as the original state.

We would then expect the rate of forward reaction to return to its original value also.

Therefore option A will be the better answer to this question.

2021 p1 q12 answer

If the pressure stays low after time t, then option B will be the better answer.

Topic: Chemical Equilibria, Physical Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2021 A Level H2 Chemistry Paper 1.

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