When an explosive is initiated either to burning or detonation, its energy is released in the form of heat. The liberation of heat under adiabatic conditions is called the heat of explosion, denoted by the letter Q. The heat of explosion provides information about the work capacity of the explosive, where the effective propellants and secondary explosives generally have high values of Q. For propellants burning in the chamber of a gun, and secondary explosives in detonating devices, the heat of explosion is conventionally expressed in terms of constant volume conditions Q _v. For rocket propellants burning in the combustion chamber of a rocket motor under conditions of free expansion to the atmosphere, it is conventional to employ constant pressure conditions. In this case, the heat of explosion is expressed as Q _p.

Consider an explosive which is initiated by a stimulus of negligible thermal proportions. The explosion can be represented by the irreversible process as shown in Figure 5.2, where Q is the value of the heat ultimately lost to the surroundings.

Figure 5.2: Schematic diagram of the irreversible explosion process

Under constant volume conditions Q _v can be calculated from the standard internal energies of formation for the products ? U ^? _{f (products)} and the standard internal energies of formation for the explosive components ? U ^? _{f (explosive components)} as shown in Equation 5.4.

A similar expression is given for the heat of explosion under...