structural:scholar_edition
Chemistry

A simple, commonly cited, chemical equation for the combustion of gunpowder is:

A balanced, but still simplified, equation is:

The exact percentages of ingredients varied greatly through the medieval period as the recipes were developed by trial and error, and needed to be updated for changing military technology.

Gunpowder does not burn as a single reaction, so the byproducts are not easily predicted. One study showed that it produced (in order of descending quantities) 55.91% solid products: potassium carbonate, potassium sulfate, potassium sulfide, sulfur, potassium nitrate, potassium thiocyanate, carbon, ammonium carbonate and 42.98% gaseous products: carbon dioxide, nitrogen, carbon monoxide, hydrogen sulfide, hydrogen, methane, 1.11% water.

Gunpowder made with less-expensive and more plentiful sodium nitrate instead of potassium nitrate (in appropriate proportions) works just as well. However, it is more hygroscopic than powders made from potassium nitrate. Muzzleloaders have been known to fire after hanging on a wall for decades in a loaded state, provided they remained dry. By contrast, gunpowder made with sodium nitrate must be kept sealed to remain stable. Gunpowder releases 3 megajoules per kilogram and contains its own oxidant. This is less than TNT (4.7 megajoules per kilogram), or gasoline (47.2 megajoules per kilogram in combustion, but gasoline requires an oxidant; for instance, an optimized gasoline and O mixture releases 10.4 megajoules per kilogram, taking into account the mass of the oxygen).

Gunpowder also has a low energy density compared to modern "smokeless" powders, and thus to achieve high energy loadings, large amounts are needed with heavy projectiles.