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Ammonium Nitrate

Author: Hans Lohninger

Ammonium nitrate, NH4NO3, is a white crystalline solid which is commonly used as a nitrogen fertilizer. Ammonium nitrate exhibits a positive enthalpy of solution (+25.7 kJ/mol) resulting in a significant temperature decrease when dissolving it in water; it is therefore used in instant cold packs. Ammonium nitrate can also be used as an oxidizing agent(1) (i.e. in ANFO, a mixture of alkanes and ammonium nitrate which is used as explosive in coal mining or in quarrels).

Ammonium nitrate is produced by the neutralisation of concentrated nitric acid (which must be free of chlorides(2)) with ammonia:

HNO3(aq) + NH3(g) ---> NH4NO3(aq)

This reaction is exothermic and generates enough heat to evaporate the water of the resulting ammonium nitrate solution. The remaining molten NH4NO3 is processed in a spray tower to form small beads, which may further processed, i.e. dried and coated to prevent caking.

When adding hydrochloric acid ammonium nitrate reacts to give ammonium chloride and nitric acid:

NH4NO3 + HCl ---> NH4Cl + HNO3

Ammonium nitrate reacts with sodium hydroxide, forming sodium nitrate and ammonia which is released as a gas:

NH4NO3 + NaOH ---> NH3 + H2O + NaNO3


(1) Ammonium nitrate may decompose explosively. A large number of accidents with a high death toll occurred in the last decades. One of the most spectacular event was the desaster at Ryongchon, North Korea, which killed 160 people and destroyed approximately 8000 homes.
(2) Chlorides act as a catalyst for the decomposition of NH4NO3 into water, oxygen and nitrogen.

Last Update: 2011-05-26