I wonder....what would be the historical implications of the total abscence of gunpowder? No Matchlocks. No Cannons. No Dynamite. No Missiles and so forth. How would the nature of warfare and history be? I can imagine it would mostly be the same up to a point but then the differences would begin to butterfly out of context.
Ummm... How?
If you want the laws of physics to be changed so explosives are impossible, then it's ASB. (Life would never have evolved, likely, certainly not humans)
If you want explosives never to be discovered, that's REALLY tough.
Absolute minimum, by the time that chemistry gets going, SOMEONE will find an explosive mixture. You do know how guncotton/nitrocellulose was discovered, right? Some guy mopped up a spill of mixed acids with a cloth and put it in front of a fire to dry. Pouf!
It's a bit surprising it took as long as it did for both guncotton and gunpowder. (Why did Europe not discover gunpowder on its own, for instance.)