Ammonium Nitrate (NH₄NO₃) — Properties, Uses & Safety

Overview

Ammonium nitrate (NH4NO3) is a white crystalline solid with a molar mass of 80.05 g/mol, composed of ammonium cations (NH4+) and nitrate anions (NO3-). It is one of the most widely used nitrogen fertilizers in the world, providing both ammonium and nitrate forms of nitrogen that plants can readily absorb. Ammonium nitrate is highly soluble in water, and its dissolution is strongly endothermic — a property exploited in instant cold packs used for treating sports injuries, where breaking an inner water pouch triggers the dissolution and produces a rapid temperature drop. However, ammonium nitrate is also a powerful oxidizer that can decompose explosively under certain conditions. When mixed with fuel oil, it forms ANFO (ammonium nitrate/fuel oil), one of the most commonly used industrial explosives for mining and quarrying. Tragic accidents involving ammonium nitrate — including the Texas City disaster of 1947 and the Beirut explosion of 2020 — underscore the importance of proper storage and handling. GHS hazard codes include H271 (may cause fire or explosion as a strong oxidizer) and H302 (harmful if swallowed). The thermal decomposition of ammonium nitrate follows different pathways depending on temperature: gentle heating produces nitrous oxide and water (NH4NO3 -> N2O + 2 H2O), while rapid decomposition at high temperatures can produce nitrogen, oxygen, and water in a violent exothermic reaction. For chemistry students, ammonium nitrate is a compelling compound that connects multiple topics. Its ionic nature and high solubility illustrate electrolyte behavior. The endothermic dissolution demonstrates enthalpy of solution and is a hands-on example of thermochemistry. Its dual role as fertilizer and explosive raises important discussions about chemical safety, regulation, and the responsibility that comes with chemical knowledge. The decomposition reactions provide examples of both endothermic and exothermic processes depending on conditions.

IUPAC Name

ammonium nitrate

CAS Number

6484-52-2

PubChem CID

22985

Molecular Formula

NH₄NO₃

Molar Mass

80.052 g/mol

State at STP

solid

Appearance

White crystalline solid