The bond energy for a C-H bond is about 413 kJ / mol in CH4 but 380 kJ / mol in CHBr3. Althoug

step 1 So in this video, we're going to talk about question four from chapter 8, which says the bond en

The bond energy for a C-H bond is about 413 kJ / mol in CH4...

The bond energy for a $\mathrm{C}-\mathrm{H}$ bond is about $413 \mathrm{~kJ} / \mathrm{mol}$ in $\mathrm{CH}_{4}$ but $380 \mathrm{~kJ} / \mathrm{mol}$ in $\mathrm{CHBr}_{3}$. Although these values are relatively close in magnitude, they are different. Explain why they are different. Does the fact that the bond energy is lower in $\mathrm{CHBr}_{3}$ make any sense? Why?

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Key Concepts

Bond Dissociation Energy

This concept measures the energy required to break a bond in a molecule, forming separate atoms or fragments. It reflects the intrinsic strength of a bond but also depends on the molecular environment, meaning that the same type of bond can have different energies in different molecules.

Electronic Effects of Substituents

Substituents attached to the carbon can exert electron-donating or electron-withdrawing effects that influence bond strength. In a molecule where other atoms (such as bromine) are bonded to the same carbon, these atoms can withdraw electron density through inductive effects, altering the electron distribution around the carbon-hydrogen bond and, in some cases, weakening it.

Molecular Environment Impact on Bond Properties

The overall molecular environment—including factors such as hybridization, bond polarity, and the spatial arrangement of substituents—plays a crucial role in determining bond energies. The presence of heavier, electronegative atoms can disrupt the orbital overlap and modify the hybridization of the central atom, leading to variations in bond dissociation energies even among similar types of bonds.

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