Energy changes
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Why is ammonium nitrate an explosive?
Rev writes
Explosives generally produce a large amount of gas and release energy in the ‘explosion’ reaction.
Ammonium nitrate NH4NO3 can decompose as follows on careful heating:
NH4NO3 (s) -> N2O(g) + 2H2O(g)
However when it explodes the dinitrogen oxide decomposes into its elements because it is unstable. The effect is that a small volume of solid produces a large volume of hot gas.
Notice that in the reaction the nitrate ion is an oxidiser. It oxidises the ammonium ion. One ion reacts with the other.
Ammonium nitrate normally needs a severe shock from a detonator to get it to explode. However stored ammonium nitrate has been to known to explode without warning.
If the explosive is contained in a fixed space the rapid production of gas creates a massive pressure which increases the effect of the explosion.
Ammonium nitrate has a relatively low detonating velocity so it is generally used in mining and quarrying where a slow push, or heave, is required rather than a shattering bang.
Never heat ammonium nitrate. It is unpredictable and can explode without warning.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 20 November 2003
