Haber process, commercial process for the synthesis of ammonia, NH₃. Pure hydrogen and nitrogen gases are mixed in the appropriate proportion, heated to between 450°C; and 600°C;, compressed to about 1,000 atmospheres pressure, and passed over a catalyst. The reaction is 3H₂+N₂⇌ 2NH₃+heat. The ammonia gas is liquefied by rapid cooling; unreacted nitrogen and hydrogen are returned to the reaction chamber. This process, developed by Fritz Haber in 1909, was the first commercially important high-pressure chemical process.