Haber process (häˈbər) [key], 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.