answered on 26 Jun 2015:
Grenades explode through the potential energy of the chemicals inside the grenade.
Once the pin is pulled in a grenade it sets off a fuse which ignites the chemical fuel inside. Because it’s in such a tiny space the pressure increases rapidly and it’s a big pressure which is why the explode as all that force needs to escape. https://thuliumj15.imascientist.org.uk/2015/06/26/how-do-grenades-explode/