An explosive chemical reaction is defined by its extreme speed and the dramatic release of energy. This process involves the rapid decomposition of a compound, resulting in the near-instantaneous production of a large volume of hot, expanding gases. The expansive force of these superheated gases generates the destructive power of an explosion. Determining the “most explosive” substance requires measuring the speed and intensity of this decomposition, moving beyond simple combustion.
Chemists are driven to synthesize novel materials, pushing the boundaries of molecular stability and energy storage. To evaluate a chemical’s power, scientists must quantify the rate at which its bonds break and the subsequent pressure its reaction generates. This search for ultimate power often involves creating molecules that are inherently unstable yet structurally dense, designed to store and violently release maximum energy.
Defining Chemical Explosivity
The difference between simple burning and a chemical explosion lies in the speed of the reaction front. Simple combustion, or deflagration, is a slow, subsonic burning that propagates by heat transfer. The reaction front moves slower than the speed of sound within the material, allowing the resulting gases to escape and expand gradually.
A true high explosive, in contrast, undergoes a process called detonation, where the reaction propagates at supersonic speeds. This rapid decomposition creates a powerful, self-sustaining pressure wave, known as a shockwave, that travels through the material. This shockwave compresses and heats the unreacted explosive ahead of it, ensuring the reaction continues at an extreme velocity.
High explosives are typically single compounds containing both a fuel (like carbon or hydrogen) and an oxidizing agent (often a nitro group, \(\text{NO}_2\)) within the same molecule. This internal arrangement eliminates the need for an external source of oxygen, allowing the molecule to decompose completely upon initiation. The explosive power comes from the swift rearrangement of the molecule’s atoms into highly stable, low-energy gas molecules, such as nitrogen gas (\(\text{N}_2\)), carbon dioxide (\(\text{CO}_2\)), and water vapor.
Metrics for Measuring Explosive Power
Quantifying explosive power requires measuring several distinct physical effects, not just the total energy released. The primary metric for comparison among high explosives is the Detonation Velocity (\(\text{DVoD}\)), which measures the speed of the shockwave traveling through the material, typically in meters per second (\(\text{m/s}\)). A higher \(\text{DVoD}\) indicates a faster, more instantaneous energy release, which is directly linked to greater destructive power.
Another measure is brisance, which describes the shattering capability or crushing effect of the explosive. Brisance is fundamentally related to the maximum pressure generated at the detonation front, known as the detonation pressure. An explosive with high brisance produces a powerful shockwave capable of fracturing hard targets, while a lower brisance explosive might produce more of a pushing or heaving effect.
The final consideration is the energy density, or heat of explosion, which measures the total chemical energy released per unit mass. A molecule with a high energy density releases a greater quantity of thermal energy and gas products. Therefore, the most powerful explosives must combine high density and structural stability to achieve the highest possible \(\text{DVoD}\) and brisance.
Candidates for the Most Explosive Title
Among high explosives, the compound HMX (Octogen) serves as a common benchmark for performance. HMX has a \(\text{DVoD}\) of approximately \(9,100 \text{ m/s}\) and a density of \(1.91 \text{ g/cm}^3\), making it a powerful component in military and civilian applications. Scientists consistently seek to surpass this performance by designing molecules with more tightly packed structures and a greater proportion of high-energy bonds.
One of the most powerful explosives ever synthesized on a practical scale is CL-20 (Hexanitrohexaazaisowurtzitane). Its complex, cage-like structure allows for an exceptionally high crystal density of \(2.04 \text{ g/cm}^3\), which directly contributes to its superior performance. CL-20 exhibits a \(\text{DVoD}\) in the range of \(9,400 \text{ to } 9,800 \text{ m/s}\), making it significantly more powerful than HMX and the current standard for high-energy-density materials.
Octanitrocubane (\(\text{ONC}\)) is theoretically even more powerful, with a predicted \(\text{DVoD}\) of around \(10,100 \text{ m/s}\). \(\text{ONC}\) is derived from the cubane structure, an eight-carbon cube whose \(90^\circ\) bond angles create immense strain energy. When \(\text{ONC}\) detonates, the release of this strain energy, combined with its high density, is predicted to yield a performance up to \(30\%\) greater than HMX. Although \(\text{ONC}\) has been successfully synthesized, the difficulty and cost of production limit its use to small, experimental quantities.
The Realm of Theoretical Explosives
The search for the ultimate chemical explosive leads to High-Energy-Density Materials (\(\text{HEDMs}\)) that are either too unstable or too complex to manufacture readily. The most promising candidates in this theoretical category are all-nitrogen compounds, such as the hypothetical \(\text{N}_8\) molecule. These substances are composed solely of nitrogen atoms held together by weak single or double bonds.
The principle behind their extreme power is the vast energy difference between these weak \(\text{N-N}\) bonds and the incredibly stable triple bond of dinitrogen gas (\(\text{N}_2\)). When an all-nitrogen compound decomposes, the transformation from multiple weak bonds into a massive volume of stable \(\text{N}_2\) gas releases energy. Calculations suggest that certain isomers of \(\text{N}_8\) could achieve a \(\text{DVoD}\) as high as \(11,620 \text{ m/s}\), surpassing all known conventional explosives.
While some simpler polynitrogen ions have been stabilized, the complex, cage-like structures required for the highest energy release remain mostly theoretical. These compounds represent the upper limit of chemical energy storage, but their extreme instability means they are confined to computational models and high-pressure laboratory environments. The most explosive chemical may be a substance that is yet to be safely brought out of the laboratory.