Changing the pressure
2 marks · HardExplain, using the idea of gaseous molecules, why changing the pressure does not influence the equilibrium position in reactions involving only solids and liquids.
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Also accept: Changing the pressure does not affect solids and liquids significantly because their particles are very close together and their concentrations do not change much with pressure.; Only gases are affected by changes in pressure, so equilibria involving only solids and liquids are not shifted by pressure changes.
Common mistakes: Stating changing pressure always affects equilibrium.; Not mentioning the lack of gases.
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Marking points
M1 · 1 mark · States or implies that only gaseous molecules are affected by changes in pressure.
A1 · 1 mark · Correctly explains that solids and liquids are not significantly affected because their particles are close together/concentration does not change much with pressure.
Worked solution
Only gases are affected by changes in pressure, because their volume and concentration change when the pressure changes.
Solids and liquids have their particles very close together, so changing pressure does not significantly alter their concentration, and therefore does not affect the position of equilibrium.