Ammonia
Ammonia (chemical formula: NH₃, systematic name: azane) is a colourless gas with a sharp, pungent odour. It is one of the most widely produced industrial chemicals in the world.
Physical Properties
| Property | Value |
|---|---|
| Molar mass | 17.031 g/mol |
| Boiling point | −33.34 °C |
| Melting point | −77.73 °C |
| Density (gas at STP) | 0.769 kg/m³ |
| Density (liquid, −33 °C) | 0.682 g/cm³ |
| Molecular shape | Trigonal pyramidal |
| Bond angle | 106.7° |
Ammonia is lighter than air and highly soluble in water. It is detectable by smell at concentrations as low as 5 ppm.
History
Ammonia was first isolated in 1756 by the Scottish physician Joseph Black. In 1785, the French chemist Claude Louis Berthollet determined its chemical composition.
The most significant development in ammonia chemistry came in 1909, when German chemist Fritz Haber and engineer Robert Le Rossignol demonstrated a process for synthesising ammonia from atmospheric nitrogen and hydrogen. This process, scaled for industrial production by Carl Bosch at BASF, became known as the Haber-Bosch process. Fritz Haber received the Nobel Prize in Chemistry in 1918 for this work.
Production
Global ammonia production reached approximately 235 million tonnes in 2021, making it one of the highest-volume industrial chemicals produced worldwide.
Haber-Bosch Process
The dominant industrial method combines nitrogen (N₂) from the air with hydrogen (H₂) derived mainly from natural gas, under high pressure and temperature in the presence of an iron catalyst:
N₂ + 3 H₂ → 2 NH₃
Biological Nitrogen Fixation
Certain bacteria and archaea fix atmospheric nitrogen into ammonia naturally. This biological process is a key part of the nitrogen cycle and underpins soil fertility.
Applications
Fertilisers
Approximately 88% of ammonia production is used in agriculture, primarily as a precursor to nitrogen fertilisers such as urea, ammonium nitrate, and ammonium sulfate. This makes the Haber-Bosch process directly responsible for feeding a large portion of the global population.
Refrigeration
Ammonia (designated R-717) is an efficient and widely used refrigerant in industrial refrigeration systems, including food storage and cold chains.
Fuel
Ammonia is being investigated and used as a carbon-free fuel for maritime shipping, aviation, and power generation, due to its high hydrogen content and established production infrastructure.
Other Uses
- Cleaning and household products
- Antimicrobial agent in food processing
- Precursor for explosives, plastics, textiles, and pharmaceuticals
Natural Occurrence
Ammonia occurs naturally throughout the solar system. On Earth, it is released into the atmosphere primarily through agricultural activity (~80%), biomass burning, and natural soil emissions. It has also been detected in interstellar space.
Safety
Ammonia is toxic by inhalation and corrosive to the eyes, skin, and respiratory tract.
| Threshold | Value |
|---|---|
| Odour detection | ~5 ppm |
| OSHA permissible limit (8h) | 25 ppm |
| NIOSH IDLH (immediately dangerous) | 300 ppm |
| Lethal concentration | >500 ppm |
Ammonia is highly toxic to aquatic organisms, particularly fish and amphibians. In mammals, metabolic pathways normally prevent it from accumulating in the bloodstream, but liver failure can cause dangerous ammonia build-up (hyperammonaemia).