Topic 7 of 7
Ammonia: choose useful industrial conditions
Reversible reactions require a balance between yield, speed and cost.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Pure onlyAmmonia: choose useful industrial conditions
Reversible reactions require a balance between yield, speed and cost.
In the Haber process, nitrogen from air reacts with hydrogen to form ammonia: N2(g) + 3H2(g) reversibly forms 2NH3(g). The syllabus connects hydrogen supply to cracking crude-oil hydrocarbons. The reverse reaction breaks ammonia down, so conversion is not necessarily complete.
Industrial plants use elevated pressure, a moderately high temperature and an iron catalyst. Ammonia is cooled and removed; unreacted nitrogen and hydrogen are recycled. A catalyst speeds attainment of the final composition without improving the equilibrium yield. This chapter uses supplied trends, not Le Chatelier's principle.
| Temperature | Ammonia yield | Time to approach final composition |
|---|---|---|
| Lower | Higher | Long |
| Intermediate | Intermediate | Practical |
| Higher | Lower | Short |
Worked example
Interpret a compromise
Given these trends, why might a manufacturer avoid the lowest temperature?
- A high eventual yield is not useful if formation is too slow.
- An intermediate temperature can give more ammonia per hour despite a lower final percentage.
- Higher pressure may improve yield in supplied data but adds compression costs and demands stronger equipment.
Use yield, production rate and cost together. Do not infer that the highest yield automatically gives the most economical operating conditions.