Question

Define exothermic and endothermic reactions on the basis of chemical bonding between reactants and products.

Answer 1

There is a heat change associated with the chemical reaction.This heat occur because the energy of the product is different from energy of reactants.

If energy of the product formed is lower than reactants , then extra energy is released in form of heat. Such reactions are called exothermic reactions. Now, this can be explained on basis of chemical bonding as follows:
If the amount of energy required to break the bonding in reactant molecules is lesser than amount of energy released in formation of newer bonds in products then reaction will be exothermic.

Similarly when the energy of the product formed is higher than reactants , then extra energy is absorbed by the system in form of heat. Such reactions are called endothermic reactions. Or
If the amount of energy required to break the bonding in reactant molecules is more than amount of energy released in formation of newer bonds in products then reaction will be endothermic.