Question

Explosion of crackers is a fast change.what is the reason

Answer 1

This is normally a chemical reaction.

It bursts to produce harmful gas like CO,etc.

Answer 2

here is answer

Because after bursting of crackers one cannot make it again (the burst crackers)as the chemical properties are changed. Hence bursting of crackers is a chemical change. But one can freeze melted chocolate and eat it as it is a physical change.