black powder is an explosive mixture, it exist as a chemical mixture,
molecular compounds & elements. To use black powder in a gun requirers ignition (additional heat) to produce the spontaneous combustion.
The delta (^H) or change in heat content is positive or exothermal reaction, yet it doesn't happen spontaneously.
Energy added to start chemical process is generally form related & transitional phase in breaking former bonds and forming new bonds.
Absolute Zero Kelvin
The environment generally supplies the energy of activiation.
As photographic (negatives) images form when salts of silver chloride & bromide react to light & then are treated with solutions (chemical procees) reduced to form metallic silver.