Bi_s bond is more stable than Bi_N bond. Give reason?
According to SHAB concept, hard acid combine with hard base and soft acid combine with soft base. Bi is hard acid and s is hard base and large size that is why Bi_s is more stable.

An Exothermic reaction releases energy into the surroundings and so the products have more potential energy then the reactants. The enthalpy change is a negative value. Whereas, an endothermic reaction involves the absorption of energy into the system and so the reactants have more potential energy than the products. The enthalpy change is a positive value. This is clearly represented in energy profile diagrams.