The Haber equation is N₂ + 3H₂ ⇌ 2NH₃. Nitrogen comes from air; the conventional route considered here obtains hydrogen from natural gas. Other hydrogen supply routes have different impacts.
The GCSE process uses about 450 °C, about 200 atmospheres and an iron catalyst. These are industrial conditions, not a school practical procedure.
The AQA variant includes cooling to separate ammonia and recycling unreacted gases. Higher tasks on both boards evaluate temperature, pressure, catalyst and production compromises.
Lower temperature favours more ammonia at equilibrium but can make the reaction slower. Higher pressure favours ammonia but increases engineering and energy costs. A catalyst helps the mixture reach equilibrium sooner. At the same temperature and pressure, it does not change the proportions of reactants and products at equilibrium.
Worked example
Choosing the lowest temperature for equilibrium yield alone ignores the time needed to make the product.
A catalyst helps reach equilibrium sooner; it does not shift the equilibrium towards ammonia.
Specification references
AQA 4.10.4.1 with Higher 4.6.2 and catalysts 4.6.1.4; Edexcel 4.15–4.16 and 5.19C, with Higher 5.20C–5.21C. Higher-tier questions include the effects of temperature and pressure on yield and rate.
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Explain why “use the lowest temperature and highest pressure possible” is an incomplete industrial decision.
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Compare equilibrium and rate.
Include engineering or energy costs.
Use the stated exothermic gas synthesis.
Example answer
Lower temperature favours ammonia at equilibrium but can make production too slow. Higher pressure favours the side with fewer gas molecules but demands stronger equipment and energy input. A workable process balances yield, time, energy and cost.
An answer to improve
The best conditions are whatever gives the highest equilibrium percentage.
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Name the system, direction and controlled conditions. Replace the unsupported claim with the causal link or evidence that is missing.
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