Question

The correct order of bond dissociation enthalpy of halogens is :

• A. $Cl _{2}> F _{2}> Br _{2}> I _{2}$
• B. $I _{2}> Br _{2}> Cl _{2}> F _{2}$
• C. $Cl _{2}> Br _{2}> F _{2}> I _{2}$
• D. $F _{2}> Cl _{2}> Br _{2}> I _{2}$

Answer 1

The Correct Option is C

 To determine the correct order of bond dissociation enthalpy of the halogens, it's important to understand the factors that influence bond dissociation enthalpy and how they apply to the halogens: fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂).

Bond dissociation enthalpy is the energy required to break a bond in a molecule. Several factors affect this, including bond strength and atomic sizes:

1. Bond Strength: Generally, the larger the atoms involved in the bond, the weaker and longer the bond tends to be, leading to lower bond dissociation enthalpy.
2. Atomic Size and Electronegativity: Smaller atoms with higher electronegativity tend to form stronger bonds.

For the diatomic halogens, the order of bond dissociation enthalpy from strongest to weakest can be explained as follows:

• Cl₂ has the highest bond dissociation enthalpy among halogens because chlorine atoms have an optimal balance between atomic size and bond strength.
• Br₂ follows because the atomic size of bromine is larger than chlorine, making the bond longer and slightly weaker.
• F₂ is next, although fluorine is small and highly electronegative, the F-F bond is weakened due to electron-electron repulsions in the small space between the two fluorine atoms.
• I₂ has the lowest bond dissociation enthalpy due to its large atomic size, leading to a long and weak bond.

Therefore, the correct order of bond dissociation enthalpy for halogens is:

\(Cl_{2} > Br_{2} > F_{2} > I_{2}\)

Justifying the options:

• Option 1: \(Cl _{2}> F _{2}> Br _{2}> I _{2}\) is incorrect because F₂ should have a lower bond dissociation enthalpy than Br₂.
• Option 2: \(I _{2}> Br _{2}> Cl _{2}> F _{2}\) is incorrect because it reverses the actual order, predicting I₂ to have the highest enthalpy.
• Option 3: \(Cl _{2}> Br _{2}> F _{2}> I _{2}\) is correct.
• Option 4: \(F _{2}> Cl _{2}> Br _{2}> I _{2}\) is incorrect as it places F₂ with a higher dissociation enthalpy than Cl₂.