Final answer:
Gunpowder is a mixed substance composed of charcoal, sulfur, and saltpeter. When heated, it undergoes a rapid and violent oxidation reaction that produces a large explosion.
Step-by-step explanation:
The mixture you are referring to is gunpowder. Gunpowder was originally developed by the Chinese in the ninth century AD and is composed of charcoal, sulfur, and saltpeter (potassium nitrate). When gunpowder is heated, it undergoes a rapid and violent oxidation reaction that produces large amounts of hot gas and an explosion.