During a chemical reaction energy must be supplied to break bonds in the reactants and energy is released when bonds in the products are formed.
Energy needed to break bonds and the energy released when bonds are formed can be calculated from bond energies.
State how the energy needed to break bonds and the energy released when bonds are formed differ in endothermic and exothermic reactions.
In endothermic reactions, the energy needed to break existing bonds is greater than the energy released when new bonds are formed. In an exothermic reaction, the energy released when new bonds are formed is greater than the energy taken in breaking the existing bonds.
