AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to interpret appropriate given data to predict the…
Full specification wording
The effect of temperature changes on equilibrium (HT only): Students should be able to interpret appropriate given data to predict the effect of a change in temperature on given reactions at equilibrium.
Le Chatelier's principle allows students to predict how a system at dynamic equilibrium responds to a temperature change.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 3
Study notes
From the checked teaching notes for this specification point.
The idea
Le Chatelier's principle allows students to predict how a system at dynamic equilibrium responds to a temperature change. If a reaction is exothermic in the forward direction, raising the temperature shifts the equilibrium position in the endothermic (reverse) direction, causing the product yield to fall. For example, if yield falls from 60% at 300 K to 30% at 500 K, the forward reaction is exothermic. Students are not required to consider the equilibrium constant (Kc) at GCSE level, focusing solely on qualitative shifts in equilibrium position.
What earns the marks
- State that a temperature change alters the equilibrium position, shifting it to counteract the change.
- Predict the qualitative effect on the yield of a named product, linking the shift to the direction of the forward reaction.
- Deduce whether a forward reaction is exothermic or endothermic by analysing yield data at different temperatures.
- Explain that an increase in temperature shifts the equilibrium in the endothermic direction to absorb the excess heat.
Common mistakes and how to put them right
Discussing the equilibrium constant (Kc).
Put it right: Focus solely on the equilibrium position and product yield.
Assuming that raising temperature always increases product yield.
Put it right: It increases yield only when the forward reaction is endothermic.
Confusing the rate of reaction with equilibrium position.
Put it right: Distinguish between reaching equilibrium faster (rate) and the final yield (position).
Exam tips
- Name the direction of shift explicitly, for example 'shifts to the left' or 'shifts towards the reactants'.
- Link the prediction to the sign of the enthalpy change or given temperature data provided in the question.
Try the lesson
The start of the The effect of temperature changes on equilibrium (HT only): Students should be able to interpret appropriate given data to predict the effect of a change in temperature on given reactions at equilibrium. lesson, made from checked teaching notes for this specification point.
Have a go first
A reversible reaction reaches equilibrium. The forward reaction is exothermic. A student raises the temperature of the reaction mixture. In which direction does the equilibrium position shift?
Listen
Le Chatelier's principle allows students to predict how a system at dynamic equilibrium responds to a temperature change. If a reaction is exothermic in the forward direction, raising the temperature shifts the equilibrium position in the endothermic (reverse) direction, causing the product yield to fall. For example, if yield falls from 60% at 300 K to 30% at 500 K, the forward reaction is exothermic. Students are not required to consider the equilibrium constant (Kc) at GCSE level, focusing solely on qualitative shifts in equilibrium position. A strong answer earns marks for these points. State that a temperature change alters the equilibrium position, shifting it to counteract the change. Predict the qualitative effect on the yield of a named product, linking the shift to the direction of the forward reaction. Deduce whether a forward reaction is exothermic or endothermic by analysing yield data at different temperatures. Explain that an increase in temperature shifts the equilibrium in the endothermic direction to absorb the excess heat. A common slip: Discussing the equilibrium constant (Kc). Instead, focus solely on the equilibrium position and product yield. Exam tip: Name the direction of shift explicitly, for example 'shifts to the left' or 'shifts towards the reactants'.
See it
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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