The effect of concentration

2 marks · Easy

The following reaction is at equilibrium in a sealed container:

Explain, in terms of concentration, what will happen to the position of equilibrium if extra KL(g) is added.

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The position of equilibrium will shift to the left (reactant side), as the system tries to decrease the added KL by producing more K2 and L2. (Le Chatelier's principle)

Also accept: It shifts to the left to reduce the concentration of KL.; Equilibrium moves towards the reactants to use up the added KL.

Common mistakes: Shifts to the right

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Marking points

M1 · 1 mark · Explains that the system tries to decrease the increased KL or use up the added KL.

A1 · 1 mark · States that the equilibrium shifts to the left/towards the reactants.

Worked solution

Adding extra KL(g) increases the concentration of a product. By Le Chatelier's principle, the system will shift to oppose the change, so it moves left to convert KL back into K2 and L2.