Question

Arrange the following bonds according to their average bond energies in descending order: C-Cl, C-Br, C-F, C-I.
A) C-Cl > C-Br > C-I > C-F
B) C-Br > C-I > C-Cl > C-F
C) C-I > C-Br > C-Cl > C-I

Answer 1

Hint: In this question, we need to check the bond length of the molecules that have been mentioned. Since bond length is inversely proportional to the bond energy, the molecules with greater bond length will have lesser bond energy.

Complete Step by Step Solution:
Bond energy is also known as bond strength or bond enthalpy. It is defined as the amount of energy which is required to break apart one mole of molecules into its components. Bond energy helps in the determination of how strong the bond is and therefore helps to predict the stability of the chemical compound.

In the question mentioned above, there is the presence of 2p-2p overlapping in the C-F bond, 2p-3p overlapping in the bond of C-Cl, 2p-4p overlapping in the C-Br molecule and 2p-5p overlapping is present in the bond of C-I. The bond length for the different types of overlapping that are mentioned above can be given as:
2p-2p < 2p-3p < 2p-4p < 2p-5p

Since we know that the bond energy is inversely proportional to bond length, therefore when the bond length will increase the bond energy of the molecule will decrease.
Hence, option D is the correct answer

Note: Bond energy should not be confused with bond dissociation energy. Bond dissociation energy is defined as the standard change in the enthalpy when a covalent bond is broken by homolysis. The major difference between these two is that the bond energy is a type of average value whereas bond dissociation energy is the particular value of a particular bond that occurs in a molecule.