| Endothermic Reaction | An Endothermic Reaction is a chemical reaction that requires energy to move forward. The net energy change is negative because more energy is required to maintain the products than the reactants. |
| Exothermic Reaction | An Exothermic Reaction is a chemical reaction that produces energy. The net energy change is positive, because the products are more stable than the reactants, resulting energy being produced. |
| Activation Energy | Activation Energy is the energy needed to start a reaction. Regardless of whether or not a reaction is endothermic (results in energy being consumed) or exothermic (results in energy being produced), a reaction must first overcome its activation energy to proceed. |
| Catalyst | A catalyst is a reagent that changes the rate of a reaction by binding with the reactants to change the reaction pathway. Note that catalysts don't actually lower the activation energy! Instead, catalysts create a brand new pathway for the reaction to use. |