Ammonium Nitrate
Properties
| State | Solid (white crystalline or granular) |
| Color | White |
| Solubility | Highly soluble in water (1900 g/L at 20°C; dissolution is endothermic) |
| Melting Point | 170°C |
| Boiling Point | Decomposes at ~210°C |
About Ammonium Nitrate
Ammonium nitrate is unique among common salts in carrying nitrogen in two oxidation states simultaneously — minus three in the ammonium cation and plus five in the nitrate anion — and most of the chemistry that makes it interesting comes from the energetic difference between those two states. The compound contains 34.5% nitrogen by mass, the highest of any solid fertilizer, and that density is what makes it the dominant top-dress fertilizer for grain crops worldwide. The same energetic arrangement is what makes ammonium nitrate a primary explosive component: the internal redox between NH4⁺ and NO3⁻ provides both fuel and oxidizer in the same molecule, and a triggering shock can propagate through bulk material if it's confined or contaminated with carbon. The catastrophic accidental detonations at Texas City (1947), West Fertilizer Plant (2013), and Beirut (2020) all involved bulk ammonium nitrate that ignited under the wrong combination of confinement, heat, and contamination. Practical handling for agricultural use mitigates this by keeping bulk material cool, dry, and free of organic matter, but the regulatory environment around storage and transport has grown progressively stricter. The dissolution of ammonium nitrate in water is sharply endothermic — about 25.7 kJ/mol absorbed — which is the chemistry behind instant cold packs: snap the inner pouch of water inside the granule-filled outer pouch and the temperature drops to roughly 0 °C in seconds.
Where you'll encounter it
If you've ever used an instant cold pack at a sports event, the white granules inside were ammonium nitrate (or sometimes urea, which works by the same mechanism), and the cold you felt was direct dissolution-driven enthalpy uptake. In agriculture, ammonium nitrate is the standard top-dress fertilizer for cool-season grain crops in most of Europe, applied at 50–200 kg N/hectare in split applications timed to plant uptake. In industrial mining and quarrying, ANFO (94% ammonium nitrate prills mixed with 6% diesel fuel) is the workhorse blasting explosive — cheaper than dynamite, safer to handle, and accounting for over 80% of the explosive volume used in surface mining and tunneling worldwide.
Common Uses
- Top-dress nitrogen fertilizer for grain and forage crops
- ANFO industrial explosive for mining and quarrying
- Endothermic-dissolution cold packs for medical and athletic use
- Controlled-decomposition source of nitrous oxide (N2O)
- Component of certain solid rocket-propellant formulations
Safety Information
Strong oxidizer that detonates under the right combination of confinement, heat, and fuel contamination. Bulk storage requires cool, dry conditions with no organic matter nearby; multiple regulatory regimes (Seveso II in the EU, Department of Homeland Security CFATS in the US) mandate inventory limits and security measures for facilities holding more than a few tonnes. Acute oral toxicity is low; the major hazard is the explosive risk, not chemical exposure. GHS H272, H319.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.