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The Effect of Temperature Changes on Equilibrium (AQA GCSE Chemistry: Combined Science)
Revision Note
The effect of temperature changes on equilibrium
Higher tier only
How does temperature affect equilibrium?
- Le Chatelier's Principle can be used to predict the effect of changes in temperature on systems in equilibrium
- To make this prediction it is necessary to know whether the reaction is exothermic or endothermic
- If the temperature of the reaction increases:
- The equilibrium will shift in the direction of the endothermic reaction
- If the temperature of a reaction decreases:
- The equilibrium will shift in the direction of the exothermic reaction
Worked example
Iodine monochloride reacts reversibly with chlorine to form iodine trichloride and the forward reaction is exothermic:
ICl (l) + Cl2 (g) ⇌ ICl3 (s)
dark brown yellow
What colour will the mixture turn when heated? Explain your answer.
Answer:
- The system will oppose the increase in temperature
- Increasing the temperature of an equilibrium reaction favours the endothermic reaction
- If the forward reaction is exothermic, then the backward reaction must be endothermic
- Therefore, the equilibrium will move to the left and produce more reactants
- This means that the colour of the mixture will become increasingly brown as the temperature increases
Examiner Tip
Remember all reversible reactions are exothermic in one direction and endothermic in the other.
Mark schemes don't usually give you a mark for stating that the system opposes the change but for the explanation of which reaction is favoured and why.
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