Exothermic & Endothermic Reactions
Every chemical reaction comes with an energy change. Reactions that release heat to the surroundings, like a hand warmer, are exothermic; those that absorb heat, like a cold pack, are endothermic. In an exothermic case reactants sit higher in energy than products; endothermic is the reverse, and the surroundings warm or cool accordingly. Put both kinds on energy diagrams and the two cases sit side by side.