Two reactants yield two products. Energy is neither created or destroyed. Energy is absorbed or released in chemical reactions. Chemical reactions can be described as endothermic or exothermic reactions. Endothermic Reactions Chemical reactions in which energy is absorbed are endothermic.
Energy is required for the reaction to occur.
The energy absorbed is often heat energy or electrical energy. Adding electrical energy to metal oxides can separate them into the pure metal and oxygen. Adding electrical energy to sodium chloride can cause the table salt to break into its original sodium and chlorine parts. Exothermic Reactions Chemical reactions in which energy is released are exothermic. The energy that is released was originally stored in the chemical bonds of the reactants.