An ordinary ziplock bag becomes a safe and spectacular laboratory, as students mix chemicals that bubble, change color, get hot, and produce gas, heat, and an odor. They experiment to determine what causes the heat in this chemical reaction. This exciting activity explores chemical change, endothermic and exothermic reactions, and is a great introduction to chemistry. Has often been adapted for lower grade levels. This “GEMS Classic” continues to be one of the most popular GEMS activities.