Question

Which of the following bonds has highest bond enthalpy?

• A. N-N in $\text{NH}_3$
• B. O=O in $\text{O}_2$
• C. C-H in $\text{CH}_4$
• D. $\text{N}\equiv\text{N}$ in $\text{N}_2$

Hint:

Bond strength follows a clear hierarchy: Triple Bonds $>$ Double Bonds $>$ Single Bonds. Since $\text{N}_2$ is the only option featuring a triple bond, it inherently possesses the highest bond enthalpy.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The problem requires identifying which specific chemical bond among the provided molecules demands the largest amount of thermal energy to break apart.

Step 2: Detailed Explanation:
Bond enthalpy values depend directly on the structural bond order, atomic sizing, and the extent of valence orbital overlap between the sharing atoms:

Bond Order Relationship: As the bond order increases between any two specific atoms (moving from a single bond to a double bond, and up to a triple bond), the atomic nuclei are pulled closer together. This significantly increases electron density in the bonding region, making the connection much stronger.

Evaluating Option D: Molecular nitrogen ($\text{N}_2$) features a exceptionally strong triple bond ($\text{N}\equiv\text{N}$), giving it a high bond order of 3. Breaking this triple bond requires an immense input of energy ($\approx 945\ \text{kJ/mol}$). By comparison, the single covalent bonds or the double bond in $\text{O}_2$ (bond order 2) have significantly lower bond enthalpies. Therefore, the triple bond in $\text{N}_2$ is the strongest.

Step 3: Final Answer: The highest bond enthalpy is held by the triple bond of $\text{N}_2$, matching option (D).