The Haber and Contact processes
The Haber and Contact processes
- These industrial processes balance yield, rate and cost.
- They use Le Chatelier's principle to choose conditions.
- Both reactions are exothermic.
The Haber process
- Makes ammonia: $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ (exothermic).
- Conditions: about $450\,°\text{C}$, $200\ \text{atm}$, iron catalyst.
- A low temperature would give more ammonia, but too slowly — so a moderate temperature is a compromise.
Practice
The Haber process makes:
The Haber process makes ammonia: N₂ + 3H₂ ⇌ 2NH₃ (exothermic).
Practice
Why is a moderate temperature (~450 °C) used in the Haber process?
The reaction is exothermic, so low temperature favours yield but is too slow; ~450 °C balances yield and rate.
Practice
High pressure increases the yield of ammonia in the Haber process because:
4 gas molecules become 2, so higher pressure shifts the equilibrium towards ammonia.
The Contact process
- Makes sulfur trioxide: $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$ (exothermic).
- Conditions: about $450\,°\text{C}$, near $1$–$2\ \text{atm}$, vanadium(V) oxide catalyst.
Practice
The Contact process uses which catalyst?
The Contact process (2SO₂ + O₂ ⇌ 2SO₃) uses a vanadium(V) oxide catalyst.
You've got it
Key idea
- both processes balance yield + rate + cost (Le Chatelier), and both are exothermic
- Haber: $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$; ~450 °C, 200 atm, iron catalyst (moderate temp = compromise)
- Contact: $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$; ~450 °C, 1–2 atm, V₂O₅ catalyst