What do we mean by the 'enthalpy' of a chemical bond? How does it help us to know whether a reaction will be endothermic (take in heat energy from the environment) or exothermic (release heat energy to the environment)?

Question

Caleb Adams · Accepted Answer

The enthalpy of a chemical reaction relates to the energy used to break all bonds that are made, and the energy released from all the bonds made. We can think of it as "a bond is a debt": we take energy out of the system when we form a bond, and to break a bond must pay back the energy, like paying off a debt.

The reaction is endothermic if more energy is needed to break every bond in the reactants than is released when new bonds are formed in the products, and vice versa.

Cameron Andrews · Answer

undefined The enthalpy of a chemical bond refers to the energy required to break the bond and separate the atoms completely. Knowing the enthalpy of bonds involved in a chemical reaction helps us determine whether the reaction will be endothermic or exothermic. If the total energy required to break the bonds in the reactants is greater than the energy released when new bonds form in the products, the reaction is endothermic. Conversely, if the energy released during bond formation in the products is greater than the energy needed to break the bonds in the reactants, the reaction is exothermic.