1.

Explain the concept of bond energy and bond dissociation energy in diatomic molecules.

Answer»

For a diatomic molecules, the bond energy is equal to the bond dissociation energy. The bond dissociation energy of a diatomic molecule is equal to the heat energy (ΔH) needed to break the bonds in one mole of molecules so that free gaseous atoms are produced.

For example

(a) The bond energy of H-H. is equal to the enthalpy change for breaking one mole of H-H bonds is H2 molecules and to produce free gaseous H atoms.

H-H (g) → 2H (g)

ΔH°d (H2, g) = ΔH° (H-H) = 436 kJ mol-1

(b) The bond energy of O = O bond is equal to the enthalpy change for breaking one mole O = O bonds in O2 molecules and to produce free gaseous O atoms.

O = O (g) → 2O (g) ΔH°d (O2, g) = ΔH° (O - O) = 498 kJ mol-1

(c) The bond energy of H-Cl bond is equal to the enthalpy change in breaking one mole H-Cl bonds in HCl molecules so that 1 mole H atoms and 1 mole Cl atoms are produced.

H-Cl (g) → H (g) + Cl (g)

ΔH°d (HCl) = Δ° (H-Cl) = 432 kJ mol-1


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