The effect of concentration
3 marks · NormalIn a laboratory, the following reversible reaction is at equilibrium: Explain, in terms of the effect of concentration, how the equilibrium position can be shifted to increase the amount of R(g) produced. Include why each change has this effect.
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Adding more P or Q, or removing R as it forms, shifts equilibrium right, increasing amount of R. Adding reactants increases their concentration and the system responds by forming more R. Removing R reduces product concentration, causing the system to replace it by making more R.
Also accept: Equilibrium shifts to right when more P or Q is added or R is removed
Common mistakes: Forgetting removal of product; Shifting equilibrium left
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States that increasing concentration of P or Q shifts equilibrium to the right (toward R).
M2 · 1 mark · Explains that adding reactants increases their concentration and the system makes more R to use them up.
M3 · 1 mark · Mentions that removing R shifts equilibrium right, and explains that system makes more R to replace what is lost.
Worked solution
To increase the amount of R(g): - Add more P or Q; this increases their concentration, so equilibrium moves right to make more R. - Remove R as it forms; this reduces R's concentration, so system shifts right to replace it and make more R.