Changing the pressure
2 marks · EasyConsider the following equilibrium:
Explain, with a reason, what would happen to the position of equilibrium if the pressure is decreased.
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The equilibrium will shift to the left (to the side with more gaseous molecules), because decreasing pressure favours the side with more gas molecules.
Also accept: It shifts to the side with the greater number of gas molecules; It shifts towards the reactants; It shifts left; More SO2 and O2 will be formed
Common mistakes: It does not shift; It shifts to the side with fewer molecules
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Marking points
M1 · 1 mark · Identifies that the equilibrium shifts left (towards more moles of gas)
M1 · 1 mark · Gives a clear reason linked to number of gaseous molecules and/or pressure
Worked solution
There are 2 moles of gas on the left (SO_2(g) + O_2(g)) and 2 moles on the right (2SO_3(g)). (Correction: Both sides have 2 moles; pressure change has no effect.)
Actually, since there are equal numbers of gas molecules on both sides, changing pressure will have no effect on the position of equilibrium.