The Haber Process
Nitrogen and hydrogen combine to make ammonia under pressure.
About this topic
The Haber process makes ammonia from nitrogen and hydrogen: N2(g) + 3H2(g) ⇌ 2NH3(g), ΔH = −92 kJ/mol. Nitrogen comes from air, hydrogen from natural gas (methane) and steam. Conditions are about 450 degrees Celsius, 200 atmospheres, with an iron catalyst. Unreacted gases are recycled, and ammonia is removed by cooling and liquefying.
The reaction is exothermic and reduces the number of gas moles from four to two. By Le Chatelier's principle, high pressure and low temperature would favour ammonia, but a low temperature makes the reaction too slow. So a compromise gives a yield of about 15 to 20 percent per pass, with recycling achieving over 95 percent overall. Very high pressure is expensive in equipment and energy. The iron catalyst speeds up the rate without changing the equilibrium.
Fritz Haber developed the method around 1909 and Carl Bosch scaled it up. It made possible artificial fertilisers, feeding roughly half the world's population today; about 80 percent of ammonia goes to fertilisers, and the rest to explosives, plastics and cleaning products. It also uses about one to two percent of world energy and releases carbon dioxide, so greener hydrogen sources are being developed.
A misconception is that the process only makes fertiliser; ammonia is also used for nitric acid and explosives. Another is that high temperature always increases yield, but here it lowers it.
Key ideas
- N₂ + 3H₂ ⇌ 2NH₃
- Iron catalyst, moderate temperature, high pressure
- Feeds half the world
Quick check
Use cases: where The Haber Process helps
- Homework: review the key idea behind The Haber Process before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Haber Process without notes.
- Visual learning: play with the interactive lab to see how The Haber Process changes when you adjust its inputs.
- Teaching a friend: explain The Haber Process in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is The Haber Process?
Nitrogen and hydrogen combine to make ammonia under pressure.
What will I learn in The Haber Process?
N₂ + 3H₂ ⇌ 2NH₃. Iron catalyst, moderate temperature, high pressure. Feeds half the world.
Is The Haber Process part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Haber Process lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Haber Process?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.