Chemical reactions can be classified as exothermic or endothermic. After studying these images and descriptions be sure to watch the Energy and Chemical Reactions animation.  

Exothermic reactions release more energy than they absorb. The reactants in exothermic reactions have higher bond energy than the products. When the bonds are broken energy is released. 

Endothermic reactions absorb more energy than they release. The reactants have lower bond energy than the products. Energy is absorbed by the reaction.