system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly happens when something explodes?

Like when someone blows up C4. I get that there's a charging blast that sets it off, but why does that cause an explosion?
gpt
There is a ton of stored up chemical energy in the C4; when it is detonated, nearly all of it is instantly converted into another form of energy: heat. When something heats up, it expands, and when you have enough thermal energy to vaporize a solid block of substance, the expansion will be massive; this causes the explosion.