Question

Define bond enthalpy in a polyatomic molecule. How does bond enthalpy vary with the electronegativity of atoms?
Also explain the Born Haber cycle with examples.

Answer 1

The bond enthalpy is defined as the energy which is required in the endothermic process for breaking the chemical bond for the formation of the two molecules or the atomic structure with alone or the shared pair of electrons.

Complete answer:
- Bond dissociation enthalpy is also known as bond enthalpy, is the amount of energy required to break the bond between two atoms or two species.
- It is a certain amount of energy supplied to a given molecule, which is capable of countering the forces of attraction between the two atoms and thus breaking the bond.
- A large amount of the dissociation energy is required for breaking the stable chemical bond.
-Bond enthalpy tends to increase with increase in the difference of the electronegativities of the atoms which are bonded.
- In polyatomic molecules, since a particular type of bond is present in different molecules or even in the same molecule does not possess the same bond enthalpy, hence the bond enthalpies are usually average values.
- The Born Haber cycle is a classic approach to measure the reaction energies. The cycle is mostly concerned with the formation of an ionic solid from the metals when reacted with a halogen or a non-metallic element like oxygen.
- This cycle is a stepwise process to calculate lattice enthalpy and the procedure is based on Hess’s law.

Note:
The bond enthalpy helps in calculating the standard enthalpy change when the bond is been cleaved between that of reactant and the product of the reaction at 0 K.