What does an energy level diagram tell me?

An energy level diagram plots the energy over the course of a reaction. By comparing the relative energies of the reactants and products, you can see whether the reaction is endothermic or exothermic.An exothermic reaction is one that gives out energy (usually in the form of heat) so feels hot. To give out energy, the products must be lower energy than the reactants. This shows as a lower line for the products than the reactants on the diagram.An endothermic reaction is the opposite. It takes in energy, and so feels cold. To need to take in energy, the products must have a higher energy than the reactants. This shows on the diagram as a higher line for the products than the reactants.