Chemistry-explosive chemistry of nitrogen

The explosive chemistry of nitrogen.

Nitrogen is a very stable molecule and has a very low energy state. For this reason the formation of nitrogen gas from a compound whose nitrogen atoms are bonded in a high energy state releases a great deal of energy. Consider the explosive decomposition of nitroglycerin according to the equation below.

4C₃H₅N₃O_9(l) => O_2(g) + 6N_2(g) + 12CO_2(g) + 10H₂O_(g)

The energy profile for this reaction is shown on the right. Notice how the reactant, nitroglycerin, is at a higher energy state than the products. The difference in the energy of the reactants and products is given off as heat.

It is important for all explosive reactions to:

- be extremely exothermic (release heat);
- produce gas. The gas produced expands violently with the heat produced by the reaction.
- occur rapidly. The rapid nature of an explosive reaction is exemplified by the comparison of the burning of 1 kg of petrol and 1 kg of T.N.T. (trinitrotoluene). 1kg of petrol, if allowed to burn completely, produces just over 30,000 kj, whereas the same mass of T.N.T. produces just over 4,000 kJ of energy. The explosive nature of T.N.T is due to the fact that the energy is released in microseconds rather than seconds, as in the case with petrol.

The explosive chemistry of nitrogen.
When we think of explosives, one element comes to mind time and time again. Nitrogen gas is a product of many explosive reactions. The compound nitroglycerin is pictured on the right. It is clear to see the importance of nitrogen in this compound.
Nitrogen is a very stable molecule and has a very low energy state. For this reason the formation of nitrogen gas from a compound whose nitrogen atoms are bonded in a high energy state releases a great deal of energy. Consider the explosive decomposition of nitroglycerin according to the equation below. 4C₃H₅N₃O_9(l) => O_2(g) + 6N_2(g) + 12CO_2(g) + 10H₂O_(g) The energy profile for this reaction is shown on the right. Notice how the reactant, nitroglycerin, is at a higher energy state than the products. The difference in the energy of the reactants and products is given off as heat.
It is important for all explosive reactions to: - be extremely exothermic (release heat); - produce gas. The gas produced expands violently with the heat produced by the reaction. - occur rapidly. The rapid nature of an explosive reaction is exemplified by the comparison of the burning of 1 kg of petrol and 1 kg of T.N.T. (trinitrotoluene). 1kg of petrol, if allowed to burn completely, produces just over 30,000 kj, whereas the same mass of T.N.T. produces just over 4,000 kJ of energy. The explosive nature of T.N.T is due to the fact that the energy is released in microseconds rather than seconds, as in the case with petrol.
Petrol can be made to burn in an explosive manner. Mixing the reactants, such as oxygen, together significantly accelerates the reaction. The building on the left in Oklahoma was destroyed by a mixture of petrol and ammonium nitrate which acted as the oxidant. Ammonium nitrate is commonly used as a fertiliser providing plants with a source of essential nitrogen.
A similar tragedy to the Oklahoma incident occurred on April 16th 1947 where the French cargo ship S.S. Grandcamp anchored off Texas City had taken on-board over 2,300 tons of the fertiliser ammonium nitrate (NH₄NO₃). At about 8.00 am a small fire started which could not be extinguished with the small fire extinguisher on-board. The hull soon filled with smoke and at 9.00 am fire erupted. Twelve minutes later the Grancamp disintegrated in a devastating explosion.
The 7,200 ton ship was lifted several metres out of the water and the resulting 5 metre tidal wave caused more havoc to the ruined commercial area. Texas City was in ruins and the eventual death toll mounted to 576. The chemistry behind this tragedy is very simple. The fertiliser was packaged in paper bags. Paper is made from an organic plant material called cellulose. The cellulose acted as a fuel while the ammonium nitrate acted as the oxidant and eventual reaction was devastating. Click to see how organic matter can act as a fuel in the presence of an oxidant. The image on the right shows the power of the blast as all the cars in nearby car parks were destroyed.
In 2020 a large storage of ammonium nitrate accidentally caught fire at the port of Beirut. What resulted was a devastating explosion creating an immense pressure wave which destroyed hundreds of buildings. The video on the right shows the incredible power of the blast and the chemistry behind this explosion.
1. Ammonium nitrate is commonly used as 2. What are the common features of an explosion? 2. Why do so many explosives contain the element nitrogen? 4. One kilogram of petrol releases more than seven times the energy as an equivalent mass of T.N.T. Yet T.N.T. is more explosive than petrol. Explain. 5. How can petrol be made into an explosive mixture? 6. Describe the chemistry behind the Grandcamp incident.