How do chemical explosives differ from mechanical explosives?

Chemical explosives and mechanical explosives differ fundamentally in the nature of the reaction they employ to produce rapidly expanding gas.1

• Chemical Explosives: These rely on a chemical reaction, such as rapid decomposition or burning, to release energy. They are the standard for virtually all engineering applications. They are categorized as either detonating (high) explosives, which involve extremely rapid decomposition and high pressure, or deflagrating (low) explosives, which involve fast burning and lower pressures.21
• Mechanical Explosives: These depend on a physical reaction rather than a chemical one. A common example is the overloading of a container with compressed air. Because they do not involve the chemical release of gas, they are sometimes used in mining environments where chemical explosives might be considered undesirable, though they see very little use otherwise.1

In summary, while both devices function by creating a volume of rapidly expanding gas in a brief period, chemical explosives utilize molecular transformation, whereas mechanical explosives rely on physical pressure release.1