Question

Question: The bond energy for the C H bond is about 413 kJ/mol in CH₄ but 380 kJ/mol in CHBr₃. Although these values are relatively close in magnitude, they are different. Explain why they are different. Does the fact that the C H

bond energy in CHBr₃ is lower make any sense? Why?

Short answer

Answer

The C H bond in bromoform is unstable due to the electronegativity of Br. The sigma bond electron density is minimized. So, the C H bond breaks

Step-by-step solution

Describing the C H bond energy in the methane molecule

The energy needed in a bond formation varies irregularly. The process of bond formation takes place in a clear way.

Process Energy required

$$\begin{gathered} {\text{CH}}_{\text{4}}\left(\text{g}\right)\to {\text{CH}}_{\text{3}}\left(\text{g}\right)\text{+ H}\left(\text{g}\right) 435 \\ {\text{CH}}_{\text{3}}\left(\text{g}\right)\to {\text{CH}}_{\text{2}}\left(\text{g}\right)\text{+ H}\left(\text{g}\right) 453 \\ {\text{CH}}_{\text{2}}\left(\text{g}\right)\to \text{CH}\left(\text{g}\right)\text{+ H}\left(\text{g}\right) 425 \\ \text{CH}\left(\text{g}\right)\to \text{C}\left(\text{g}\right)\text{+ H}\left(\text{g}\right) 339 \end{gathered}$$

Total = 1652 KJ/mol

Average = role="math" localid="1663761543465" $\frac{1652}{4}=413\text{KJ/mol}$

The average has taken to calculate the C-H bond energy.

Describing the C H bond energy

The average of bond energy is used as a better method even though we assume the approximation of the energy correlation with the C H bond.

Energy needed to break C-H bond in =413 kJ/mol

Energy needed to break C-H bond in =380 kJ/mol

Thedegree of sensitivity of the bondcan be calculated by the experimental value of the energy required for the CH bond.

The stronger bond requires a larger amount of energy. Thus, methane has a stronger bond while bromoform does not.