AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
If the temperature of a system at equilibrium is increased: the relative…
Full specification wording
The effect of temperature changes on equilibrium (HT only): If the temperature of a system at equilibrium is increased: the relative amount of products at equilibrium increases for an endothermic reaction the relative amount of products at equilibrium decreases for an exothermic reaction.
Changing temperature affects the position of equilibrium because it changes the rates of the forward and reverse reactions differently, depending on whether the forward reaction is endothermic or…
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 3
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Changing temperature affects the position of equilibrium because it changes the rates of the forward and reverse reactions differently, depending on whether the forward reaction is endothermic or exothermic. If the temperature is increased, the system absorbs the extra heat by favouring the endothermic direction. For an endothermic forward reaction, the forward reaction is favoured, so the relative amount of products at equilibrium increases. For an exothermic forward reaction, the reverse reaction is endothermic and is favoured instead, so the relative amount of products at equilibrium decreases.
For example: In the endothermic forward reaction N₂O₄(g) ⇌ 2NO₂(g), increasing temperature shifts equilibrium to the right, producing more NO₂.
What earns the marks
- Increasing temperature favours the endothermic direction.
- For an endothermic forward reaction, the forward reaction is favoured and the relative amount of products increases.
- For an exothermic forward reaction, the reverse reaction is favoured and the relative amount of products decreases.
- The system absorbs the added heat by shifting in the endothermic direction.
- The new equilibrium has a different composition from the original equilibrium.
- The explanation should refer to the relative amounts of products, not just the direction of the shift.
Common mistakes and how to put them right
Assuming that increasing temperature always increases the amount of product.
Put it right: This is only true for an endothermic forward reaction.
Confusing endothermic and exothermic directions.
Put it right: The endothermic direction is always favoured when temperature increases.
Thinking that temperature changes affect only the rate and not the position of equilibrium.
Put it right: Temperature changes affect both.
Exam tips
- State whether the forward reaction is endothermic or exothermic before predicting the effect.
- Use the phrase 'the equilibrium shifts in the endothermic direction' to show clear reasoning.
- Link the prediction to the relative amount of products at the new equilibrium.
Try the lesson
The start of the The effect of temperature changes on equilibrium (HT only): If the temperature of a system at equilibrium is increased: the relative amount of products at equilibrium increases for an endothermic reaction the relative amount of products at equilibrium decreases for an exothermic reaction. lesson, made from checked teaching notes for this specification point.
Have a go first
A reversible reaction reaches equilibrium. The forward reaction is endothermic. The temperature of the system is then increased. What happens to the relative amount of products at equilibrium?
Listen
Changing temperature affects the position of equilibrium because it changes the rates of the forward and reverse reactions differently, depending on whether the forward reaction is endothermic or exothermic. If the temperature is increased, the system absorbs the extra heat by favouring the endothermic direction. For an endothermic forward reaction, the forward reaction is favoured, so the relative amount of products at equilibrium increases. For an exothermic forward reaction, the reverse reaction is endothermic and is favoured instead, so the relative amount of products at equilibrium decreases. For example, in the endothermic forward reaction N₂O₄(g) ⇌ 2NO₂(g), increasing temperature shifts equilibrium to the right, producing more NO₂. A strong answer earns marks for these points. Increasing temperature favours the endothermic direction. For an endothermic forward reaction, the forward reaction is favoured and the relative amount of products increases. For an exothermic forward reaction, the reverse reaction is favoured and the relative amount of products decreases. The system absorbs the added heat by shifting in the endothermic direction. Exam tip: State whether the forward reaction is endothermic or exothermic before predicting the effect.
See it
Key words
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Endothermic and exothermic reactions
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Equilibrium position
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Temperature changes
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See every definition
- Endothermic and exothermic reactions
- When temperature is increased, the system absorbs the extra heat by favouring the endothermic direction, while for an exothermic reaction the relative amount of products at equilibrium decreases.
- Equilibrium position
- Changing temperature affects the position of equilibrium because it changes the rates of the forward and reverse reactions differently, depending on whether the forward reaction is endothermic or exothermic.
- Temperature changes
- If the temperature of a system at equilibrium is increased, the relative amount of products at equilibrium increases for an endothermic reaction and decreases for an exothermic reaction.
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