HL only: Subtopic 2.3: Biogeochemical cycles
The Haber process is an industrial process that reacts atmospheric nitrogen with hydrogen to produce ammonia. It is important because ammonia is used to manufacture synthetic fertilizers, increasing crop productivity and supporting global food production.
The Reasoning and Mechanism
Atmospheric nitrogen exists mainly as nitrogen gas, . Although nitrogen is essential for producing amino acids and proteins, plants cannot use atmospheric directly; it must first be converted into biologically available nitrogen compounds.
The Haber process carries out this conversion industrially:
The resulting ammonia, , is used to produce nitrogen-containing fertilizers. Plants absorb nitrogen compounds from soil and use them to produce biomass, so fertilizer application can raise crop yields and help improve food security. Haber-based fertilizers were particularly important to the increased agricultural productivity associated with the Green Revolution.
However, the process and its products can reduce environmental sustainability.
| Agricultural importance | Environmental or social limitation |
|---|---|
| Replaces nitrogen removed when crops are harvested | Fertilizer production requires substantial energy, often supplied by fossil fuels |
| Increases productivity in intensive farming systems | Excess fertilizer can enter water through runoff or leaching |
| Supports food production for large populations | Nitrate and phosphate inputs can cause eutrophication |
| Reduces immediate dependence on natural nitrogen fixation | Unequal access to fertilizer can reinforce economic inequalities between farmers |
A common misconception is that the Haber process fixes nitrogen naturally. It is industrial nitrogen fixation; natural nitrogen fixation is carried out by certain bacteria.
Exam Technique
For an IB ESS question, link the Haber process to human disruption of the nitrogen cycle: identify the conversion of atmospheric nitrogen into ammonia, explain increased agricultural productivity, and then connect excess fertilizer use to nitrate pollution and eutrophication. This content is HL only, so SL students are not required to learn syllabus understanding 2.3.23.