When evaluating a chemical's potential for explosion, which intrinsic property, beyond simple flammability, signifies an unstable molecular structure prone to rapid decomposition and energy release?

The intrinsic property that signifies an unstable molecular structure prone to rapid decomposition and energy release, beyond simple flammability, is its heat of decomposition.

Flammability refers to a substance's ability to burn or ignite easily, requiring an external ignition source and oxygen. Explosives, however, possess an inherent instability that allows them to decompose very rapidly, releasing a large amount of energy and gas without needing external oxygen. This rapid decomposition is the core of an explosion.

Heat of decomposition is the amount of energy (heat) released when a substance breaks down into simpler components. For explosive materials, this decomposition is extremely fast and exothermic, meaning it releases a significant amount of heat. This released heat then rapidly heats the decomposition products (gases), causing them to expand violently, creating the explosive pressure wave. A high positive heat of decomposition indicates that the chemical bonds within the molecule store a lot of potential energy. When these bonds break during decomposition, this stored energy is released rapidly. Molecules that are unstable often have weak bonds or a strained arrangement of atoms, making them prone to breaking apart easily and releasing energy.

For instance, nitroglycerin has a very high positive heat of decomposition. When detonated, its molecules break down extremely quickly, releasing a vast amount of energy and gaseous products. This rapid energy release causes the characteristic explosion. Simple flammable materials like wood, while they release heat when they burn, do so at a much slower rate and rely on external oxygen. Their heat of decomposition is not the primary factor dictating explosive potential; rather, it's their flammability and combustion rate.

Therefore, while flammability is about reaction with oxygen, the heat of decomposition directly measures the inherent energy stored within the molecule that can be released explosively through self-sustaining, rapid internal breakdown.