Q80 · Practice questionComplex familiar5 marks
QUESTION 80 (5 marks)
The Haber reaction is , with . A designer considers lowering the operating temperature from 450 °C to 100 °C while keeping the pressure fixed.
a) Predict the change in equilibrium yield and explain. [2 marks]
b) Explain why the lower temperature may reduce ammonia production per hour despite the improved equilibrium yield. [2 marks]
c) State the catalyst’s effect on the equilibrium yield. [1 marks]
WORKED SOLUTION
5 marksPractice marking scheme
Lower temperature raises equilibrium ammonia yield, but may make the reaction too slow. A catalyst changes rates and time to equilibrium, not equilibrium yield.
Cooling favours the exothermic forward reaction. Fewer collisions have sufficient activation energy at lower temperature, so a plant may produce less product in a fixed time. A catalyst lowers activation barriers for both directions.
- Predicts increased equilibrium yield. [1 marks]
- Uses exothermic forward reaction to justify. [1 marks]
- Predicts a lower reaction rate. [1 marks]
- Explains smaller fraction of successful collisions. [1 marks]
- States catalyst does not change equilibrium yield. [1 marks]
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