Making and breaking of bonds are examples of chemical reaction. Chemical bonding is the process in which chemical bonds are formed and the process of breaking of bonds is called chemical dissociation.
It takes energy to break the chemical bond between the reactants and the making of new bonds gives the energy. Therefore breaking of bond is an endothermic process and making of bond is an exothermic process.
Bonds breaks when a particular amount of energy is given to it and this energy is called the bond energy.