Bond enthalpy and enthalpy of reaction | Chemistry

Bond enthalpy is the energy required to break one mole of a specific type of bond in a gaseous molecule. It is usually represented as ΔH or ΔHrxn.

Enthalpy of reaction, also known as heat of reaction, is the change in enthalpy that occurs during a chemical reaction when the reactants are converted into products. It is also represented as ΔH or ΔHrxn.

The relationship between bond enthalpy and enthalpy of reaction can be explained using the concept of bond breaking and bond forming.

In a chemical reaction, bonds in the reactant molecules are broken, and new bonds are formed in the product molecules. The energy required to break the bonds (bond enthalpy) is an endothermic process, as energy needs to be supplied to weaken the bonds.

On the other hand, the energy released when new bonds are formed (bond formation) is an exothermic process, as energy is released during the formation of stronger bonds.

The enthalpy of reaction is the net energy change in the reaction, taking into account the energy required to break the bonds and the energy released when new bonds are formed.

Mathematically, the enthalpy of reaction (ΔHrxn) can be calculated using the bond enthalpies of the bonds broken (ΣΔHbroken) and the bond enthalpies of the bonds formed (ΣΔHformed):

ΔHrxn = ΣΔHformed - ΣΔHbroken

If the sum of the bond energies for the bonds broken is greater than the sum of the bond energies for the bonds formed, then the ΔHrxn will be positive, indicating an endothermic reaction. Conversely, if the sum of the energies for the bonds formed is greater than the sum of the energies for the bonds broken, then the ΔHrxn will be negative, indicating an exothermic reaction.