The Haber process: ammonia and a practical compromise
Connect the equation, feed sources and typical conditions with reaction rate, equilibrium and plant demands.
Extended only (Supplement) · Chemistry 0620, 2026–2028. The conditions are the typical syllabus values, not operating instructions for a plant.
Before you begin
- Predict equilibrium responses for exothermic reactions and unequal gas counts.
- Explain pressure, temperature and catalyst effects on reaction rate.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many gaseous coefficient parts occur on each side of N₂+3H₂⇌2NH₃?
What you will learn
- State the Haber equation, nitrogen and hydrogen sources, and typical syllabus conditions.
- Explain the temperature, pressure and catalyst choices through rate, equilibrium, safety and economics.
Identify the reaction and its feeds
The Haber process forms ammonia by N₂(g)+3H₂(g)⇌2NH₃(g). The forward reaction is exothermic. Nitrogen is obtained from air, while methane is the stated source used to obtain hydrogen in the syllabus industrial route. Methane is a feedstock for making hydrogen; it is not substituted for H₂ in the ammonia equilibrium equation.
The typical syllabus conditions are about 450 °C, 20 000 kPa (about 200 atm), with an iron catalyst. Keep the units and catalyst separate: the temperature is not 450 K, and 200 atm is much higher pressure than the Contact process's stated 2 atm. These are typical examination values; real plant designs can use operating ranges rather than one universal exact setting.
Explain the compromise, rather than just reciting it
A lower temperature favours the exothermic ammonia-producing direction and improves equilibrium yield, but makes the reaction too slow for a useful production rate. About 450 °C is the syllabus compromise between speed and equilibrium proportion. Higher pressure favours the two gas-particle coefficient parts of ammonia over four on the reactant side, and can also increase collision frequency, but demanding ever higher pressure increases compression costs and the need for stronger equipment and safe containment.
An iron catalyst provides a faster route so equilibrium can be approached at a useful rate; it does not change the equilibrium yield at the same temperature. Product removal and recycling unreacted nitrogen and hydrogen help use the feeds effectively across repeated passes. Distinguish single-pass equilibrium conversion from total plant production, and compare the economic benefit of more product with the energy, equipment and safety demands of the conditions.
Pause and explain
Why does an iron catalyst help the Haber process?
Worked example
A proposal lowers Haber temperature far below 450 °C and raises pressure far above 200 atm to maximise equilibrium ammonia. Evaluate why an industrial choice also needs a rate and cost argument.
Show the worked solution
- Lower temperature favours equilibrium ammonia because the forward reaction is exothermic, but it also slows reaction.
- Higher pressure favours ammonia's smaller gas-particle total, but requires more demanding compression and pressure-resistant equipment.
- The stated typical temperature and pressure balance useful production rate and yield with energy, equipment and safety demands; an iron catalyst speeds the approach without shifting equilibrium.
Answer Equilibrium yield alone is insufficient; the conditions must also support useful rate and manageable plant demands.
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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the Haber equation, feed sources and typical conditions, then connect one condition to its purpose.
Give me a hint
Keep raw-material sources separate from the reactants in the equilibrium equation.
Compare my reasoning
- N₂(g)+3H₂(g)⇌2NH₃(g); nitrogen comes from air and hydrogen is obtained using methane in the stated route.
- Use about 450 °C, 20 000 kPa/about 200 atm, and an iron catalyst.
- Pressure favours the fewer-gas-particle ammonia side; temperature balances rate with exothermic equilibrium yield.
N₂+3H₂⇌2NH₃; air/methane sources; 450 °C, about 200 atm, iron.
Look for these in your work
- Equation and feed sources are not confused.
- A condition has an explained role.
Explain the separate consequences of lowering temperature, increasing pressure and adding a catalyst for Haber equilibrium and production rate.
Give me a hint
Give an equilibrium conclusion and a rate conclusion where each applies.
Compare my reasoning
- Lower temperature increases the equilibrium ammonia proportion but slows reaction.
- Higher pressure favours ammonia and can increase collision frequency, while increasing compression and equipment demands.
- A catalyst speeds both directions and approach to equilibrium without changing the position at fixed temperature.
Temperature trades rate against yield; pressure favours ammonia with plant demands; catalyst changes speed, not equilibrium position.
Look for these in your work
- Rate and yield are kept distinct.
- Practical consequences accompany the favourable equilibrium change.
A hypothetical pass starts with 1.0 mol N₂ and 3.0 mol H₂ and forms 0.40 mol NH₃ before separation. Find amounts of unreacted gases and explain the purpose of recycling them. Assume no losses or side reactions.
Give me a hint
For every two moles NH₃, one N₂ and three H₂ are consumed.
Compare my reasoning
- Producing 0.40 mol NH₃ uses 0.20 mol N₂ and 0.60 mol H₂.
- Unreacted amounts are 1.0−0.20=0.80 mol N₂ and 3.0−0.60=2.40 mol H₂.
- Recycling uses these remaining feeds in later passes, rather than discarding them; it does not mean the single pass converted all reactants.
0.80 mol N₂ and 2.40 mol H₂ remain for possible recycling.
Look for these in your work
- The 1:3:2 equation fixes consumption.
- Recycling is distinguished from complete single-pass conversion.
Common mistakes
- Writing methane instead of hydrogen in the ammonia equilibrium equation.
- Calling 450 °C the condition that gives the maximum equilibrium yield.
- Claiming the iron catalyst increases equilibrium ammonia proportion.
- Confusing Haber pressure 200 atm with Contact pressure 2 atm.
What can you explain now?
State the typical Haber temperature, pressure and catalyst used by this syllabus.
Compare with the explanation
450 °C; 20 000 kPa (about 200 atm); iron catalyst.
These values describe the typical rate–equilibrium compromise; lower temperature favours yield but slows reaction, and higher pressure has equipment and cost demands.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Write the Haber facts without notes, then explain each typical condition in a rate–yield–plant-demand comparison. Include why a catalyst and recycling do different jobs.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.