Page "Explosive material" Paragraph 27

* Chemical constitution.

In the strictest technical sense, the word " stability " is a thermodynamic term referring to the energy of a substance relative to a reference state or to some other substance.

However, in the context of explosives, stability commonly refers to ease of detonation, which is concerned with kinetics ( i. e., rate of decomposition ).

It is perhaps best, then, to differentiate between the terms thermodynamically stable and kinetically stable by referring to the latter as " inert.

" Contrarily, a kinetically unstable substance is said to be " labile.

" It is generally recognized that certain groups like nitro (– NO < sub > 2 </ sub >), nitrate (– ONO < sub > 2 </ sub >), and azide (– N < sub > 3 </ sub >), are intrinsically labile.

Kinetically, there exists a low activation barrier to the decomposition reaction.

Consequently, these compounds exhibit high sensitivity to flame or mechanical shock.

The chemical bonding in these compounds is characterized as predominantly covalent and thus they are not thermodynamically stabilized by a high ionic-lattice energy.

Furthermore, they generally have positive enthalpies of formation and there is little mechanistic hindrance to internal molecular rearrangement to yield the more thermodynamically stable ( more strongly bonded ) decomposition products.

For example, in lead azide, Pb ( N < sub > 3 </ sub >)< sub > 2 </ sub >, the nitrogen atoms are already bonded to one another, so decomposition into Pb and N < sub > 2 </ sub >.< sup ></ sup > is relatively easy.