Justin bleeber is conducting a calorimetry experiment in chemistry class. he fills an empty soda can with water and hangs it from an iron ring. the can hangs above a cracker that is resting on a stand. justin uses his striker to light a bunsen burner. he uses the flame from the bunsen burner to light a wooden splint. the wooden splint is used to ignite the cracker. as the cracker burns it heats up the water in the soda can. waves of gas are seen coming out of the top of the can. how many chemical changes did justin observe?