Changing the temperature

2 marks · Hard

For the following equilibrium reaction:

State how increasing the temperature will affect the position of equilibrium. Give your answer for both cases: (i) forward reaction is exothermic; (ii) forward reaction is endothermic.

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(i) If forward is exothermic: equilibrium shifts to the left (reverse reaction). (ii) If forward is endothermic: equilibrium shifts to the right (forward reaction).

Also accept: (i) Exothermic forward: left; (ii) Endothermic forward: right.; Increase T: favours endothermic direction — left if forward is exothermic, right if forward is endothermic.

Common mistakes: Reversing the directions for exothermic/endothermic.; Stating the position doesn’t change.

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Marking points

B1 · 1 mark · States the correct direction for case (i): left (reverse) if forward exothermic.

B2 · 1 mark · States the correct direction for case (ii): right (forward) if forward endothermic.

Worked solution

(i) If the forward reaction is exothermic, increasing temperature favours the endothermic (reverse) reaction, so equilibrium shifts to the left.

(ii) If the forward reaction is endothermic, increasing temperature favours the forward reaction, so equilibrium shifts to the right.