For example when zinc combines with hydrochloric acid, the zinc replaces hydrogen. So, a part of one of the reactants trades places and is in a different place among the products. In a double replacement reaction parts of two compounds switch places to form two new compounds. 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.