Question

The correct sequence of bond enthalpy of ‘C–X’ bond is

• A. CH₃−Cl > CH₃−F > CH₃−Br > CH₃−I
• B. CH₃−F < CH₃−Cl < CH₃−Br < CH₃−I
• C. CH₃−F > CH₃−Cl > CH₃−Br > CH₃−I
• D. CH₃−F < CH₃−Cl > CH₃−Br > CH₃−I

Answer 1

The Correct Option is C

To determine the correct sequence of bond enthalpy for the ‘C–X’ bond in methyl halides, we must understand the concept of bond enthalpy, which is the measure of bond strength in a chemical bond.

Bond Enthalpy Explanation: Bond enthalpy is the energy required to break one mole of bonds in gaseous molecules. A higher bond enthalpy indicates a stronger bond. The bond enthalpy of a C–X bond decreases as we move down the halogen group (F, Cl, Br, I) due to increased atomic size and decreased electronegativity.

Comparison of C–X Bonds:

• CH_3-F: The C–F bond is the strongest among methyl halides due to the high electronegativity and small size of fluorine.
• CH_3-Cl: The C–Cl bond is weaker than C–F but stronger than C–Br and C–I.
• CH_3-Br: The C–Br bond is weaker due to the larger size of bromine compared to chlorine.
• CH_3-I: The C–I bond is the weakest due to the largest size of iodine, leading to the longest bond length.

From this understanding, the correct sequence of bond enthalpies is:

CH_3-F > CH_3-Cl > CH_3-Br > CH_3-I

Conclusion: The correct answer is CH₃−F > CH₃−Cl > CH₃−Br > CH₃−I because bond strength decreases as the size of the halogen increases. This trend matches the provided option and confirms our understanding of bond enthalpies in methyl halides.