The Haber process and the use of NPK fertilisers

• The Haber process is used to manufacture ammonia, which is used to produce nitrogen-based fertilisers.
• The raw materials for the Haber process are nitrogen and hydrogen.
• Nitrogen is obtained from the air and hydrogen may be obtained from natural gas or other sources.
• The purified gases are passed over a catalyst of iron at a high temperature (about 450 °C) and a high pressure (about 200 atmospheres) in the Haber process.
• Some of the hydrogen and nitrogen reacts to form ammonia in the Haber process.
• The reaction in the Haber process is reversible so ammonia breaks down again into nitrogen and hydrogen.
• On cooling, the ammonia liquefies and is removed in the Haber process.
• The remaining nitrogen and hydrogen are recycled in the Haber process.
• The Haber Process is in dynamic equilibrium, meaning the forward and backward reactions keep going once equilibrium is reached.
• The chemical equation for the Haber process is N2 + 3H2 ⇋ 2NH3, indicating there are fewer moles of gas on the product side (2 compared to 4), which means more pressure is needed to move equilibrium to the right and produce more ammonia.
• The forwards reaction in the Haber process is exothermic, meaning a low temperature would favour the forwards reaction and produce more ammonia.
• Industrial production of NPK fertilisers can be achieved using a variety of raw materials in several integrated processes.
• NPK fertilisers contain compounds of all three elements.
• Ammonia can be used to manufacture ammonium salts and nitric acid.
• Potassium chloride, potassium sulfate and phosphate rock are obtained by mining, but phosphate rock cannot be used directly as a fertiliser.
• Phosphate rock is treated with nitric acid or sulfuric acid to produce soluble salts that can be used as NPK fertilisers.