REACTIONS |Chemical reactions occur by breaking or making bonds. There are oficn 2 or3 key parts ofa reactioni ed - Subsianccs cxisting before th reaction o =。。 = Subsanccs existing after the reacHon o 。。 -Subsances which specd up the rate of a reaction |Chemical equatioms are a shorthand way ofshowing chemical rcactions. Most rcactions naturally when they release cnergy. Reactions that rclease cnergy are called lowever, ienersy is added, (hat can cause reactions to happen that nonnally wouldn't 語了sa actions (har abaob'cnengy are called >