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CAIE A-Level Chemistry 7.1.10 Haber and Contact Process Conditions

Practise explaining industrial temperature, pressure and catalyst choices as compromises between yield, rate and cost.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • apply Le Chatelier’s principle and reaction enthalpy to explain the chosen operating temperature
  • compare gaseous mole totals to explain the pressure choice, then balance yield against compression cost
  • explain that the catalyst increases reaction rate without changing K or the equilibrium yield

7.1.10—Conditions used in the Haber process question 1

[Maximum number: 2]

Ammonium nitrate is an important fertiliser made by the acid-base reaction between ammonia and nitric acid.

The Haber process involves a reaction between nitrogen and hydrogen at a temperature of 450∘C450^{\circ} \mathrm{C} and a pressure of 20000 kPa . At a higher reaction temperature, the rate of production of ammonia would be greater.

N2( g)+3H2( g)⇌2NH3ΔH=−92 kJ mol−1\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3} \quad \Delta H=-92 \mathrm{~kJ} \mathrm{~mol}^{-1}

The Boltzmann distribution curve shows the distribution of energies in a mixture of nitrogen and hydrogen at 450∘C450^{\circ} \mathrm{C}.

Figure for Question 7.1.10—Conditions used in the Haber process question 1 — CAIE A-Level Chemistry AS

Explain why a higher temperature is not used despite the fact that it would increase the rate of production of ammonia.

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