In today’s session we started our investigation into thermodynamic principles. We defined a chemical reaction and classified two types – exothermic and endothermic. The students demonstrated both types of reactions: acetic acid + baking soda (exothermic) and yeast + hydrogen peroxide (endothermic). While carrying out the reactions, students thought about how the first law of thermodynamics (conservation of energy) applied to a reaction that seems to create energy. The takeaway was that energy stored in the bonds of the reactants is the source of the heat released in an exothermic reaction.