Imagine a stretched rubber band, what happens when you cut the middle? The stress contained within is released. All reactions that release energy do varying amounts of this.
Chemical ones utilize forces between electrons, they are rather weak (compared to nucleus forces).
An atom’s nucleus however has very strong forces holding it together, if you manage to split it, you release all that, causing a much bigger release than would happen with chemical reactions.
In actuality, it is a bit more complicated, heavier atoms, you would use fission to release energy. Lighter atoms you use fusion to gain energy, but this is ELI5 anyway.
Latest Answers