How could I shoot a chemical in a fire extinguisher?

kinda interesting idea. I suggest you look into walkerboystudios.com They have 5 free labs that teach some basics about different game styles. Pointnclick, 2d, 3d, even a tool lab that can help with 2d sprites and gui functions. the point is its free and has no obligation. specifically look at the 2d mario lab. It has a part that shows how to instantiate the fireball with an input command. I think it would be better for you to go through this to figure out how to do what you want rather than someone tell you. the difference is instead of calling up the fireball sprite you need to make a partcile effect for the chemical. =) have fun!