A useful compromise.
The Haber process makes ammonia by N₂ + 3H₂ ⇌ 2NH₃. Higher pressure favours ammonia because fewer gas moles occur on the product side. Lower temperature favours equilibrium yield because the forward reaction is exothermic, but also slows reaction. A practical process balances rate, yield, cost and safety.
A catalyst increases rate without changing K. Cooling removes ammonia, and unreacted gases can be recycled. The operating choices must be justified together rather than described as a single perfect condition.
In the contact process, sulfur is burned to SO₂; 2SO₂ + O₂ ⇌ 2SO₃ is catalysed by V₂O₅. SO₃ is absorbed in sulfuric acid to form oleum and then carefully diluted. Directly adding SO₃ to water creates a troublesome acid mist.
A balance that keeps moving
Illustrative A ⇌ B model in a closed system; total concentration 1.00 mol L⁻¹. Ratio K = [B]/[A]. Not a model of any particular industrial reaction.
Explore: Shift the synthesis balance and weigh equilibrium yield against reaction rate.
Why does an ammonia plant use a moderate temperature rather than the lowest possible temperature?
- Exothermic synthesis favours lower temperature at equilibrium.
- A higher operating temperature gives a useful rate.
Answer: Low temperature favours equilibrium yield but makes the rate too slow; a moderate temperature balances yield and rate.
Assumed knowledge
Le Châtelier’s principle and activation energy.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Connect industrial conditions with yield and rate.
- Write the key synthesis equations.
- Interpret the role of catalysts and recycling.