Hi,

What are the physical and chemical changes that occur infireworks?
http://www.fireworkfactory.com/

They use gunpowder to create the explosion. Gunpowder contains sulphur and potassium nitrate.

O, i see. So the firework is just like a mini rocket i guess. Thx

A firework will popularly use black powder as suggested (or otherwise known as Gun Powder). This is a mix between Potassium Nitrate, Sulphur and Activated Charcoal (KNO3, S and C)
The Caesium and water made me laugh, Caesium is highly dangerous, can you imagine what would happen if the firework was left in a damp enviornment? eg. a shed?
The sparkles and stuff can be made using different metals, eg for a green flame, they would use copper, iron filings in a fire would produce golden sparkles, magnesium would provide a bright, almost blinding white light, titanium has also been used before.

Where I said a firework uses black powder this isnt always strictly true, chinese fireworks have used M80 before and other similar mixtures