Changing the temperature
4 marks · NormalThe equation below shows a reversible reaction.
Is the forward reaction exothermic or endothermic? Explain your answer.
Predict what happens to the position of equilibrium if the temperature is decreased. Explain your answer.
Which direction (left or right) is favoured when temperature is increased? Explain.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Endothermic, because ΔH is positive.
(b) Decreasing temperature favours the exothermic direction (left), so equilibrium shifts towards X2.
(c) The right (forward) direction, because that is endothermic and absorbs heat.
Common mistakes: Misidentifying forward reaction type; Mixing up temperature effect
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Marking points
M1 (a) · 1 mark · States forward reaction is endothermic because ΔH is positive.
M2 (b) · 1 mark · States equilibrium shifts to exothermic direction/left/towards X2 at lower temperature.
M3 (b) · 1 mark · Explains that this is because exothermic direction is favoured to release heat.
B1 (c) · 1 mark · States right/forward is favoured at higher temperature, as it is endothermic and absorbs heat.
Worked solution
(a) Forward reaction is endothermic because ΔH is +160 kJ/mol.
(b) When temperature is decreased, the equilibrium favours the exothermic direction (left), producing more X2 to give out heat.
(c) The right (forward) direction, because it is endothermic and absorbs heat when temperature is increased.