What type of explosion occurs when the reaction front travels slower than the speed of sound in the unreacted medium?

Deflagration is characterized by a reaction front that moves at a speed slower than the speed of sound in the unreacted medium. This type of explosion typically involves a rapid but subsonic combustion process, where the combustion waves propagate through the material at velocities less than the sound speed in that material.

In deflagration, the heat generated by the reaction heats the adjacent portions of the explosive material, causing them to react, but this propagation of the reaction occurs at a slower pace than the sound waves traveling through the material. This can lead to a relatively controlled release of energy, which is often typical in lower-energy explosives and pyrotechnics.

In contrast, a detonation involves a reaction that surpasses the speed of sound, resulting in a shock wave that causes a much more violent explosion. Combustion refers to any rapid oxidation reaction, which may not involve a wave front, and thermal explosions refer to reactions initiated by heat but do not specifically dictate the speed of the reaction front. Thus, deflagration accurately describes the scenario posed in the question.