Bond energy is defined by the sum of all of the bonds broken minus the sum of all of the bonds formed: ΔH = ∑H_{(bonds broken)} - ∑H_{(bonds formed)}. ΔH is the change in bond energy, also referred to as the bond enthalpy and ∑H is the sum of the bond energies for each side of the equation.

The C-C vs C-H Bond Strength The relative size of the s orbital explains also why the C-C σ bond is weaker than the C-H σ bond. And that is because the hydrogen uses a “pure” s orbital (100% s character) which is closer to the nucleus than is the sp³ orbital of carbon.

Answer and Explanation: Due to hyperconjugation, the tertiary carbon atom is more stablized when the C-Hd bond is broken. Primary and Secondary Carbons are less stabilized. Thus, the C-Hd is the weakest bond.

The stronger bond is in the molecule with the more electronegative atom involved. For instance, the bonds in CCl4 are stronger than those of the CBr4 because Cl has a higher electronegativity than Br due to Cl's smaller size. Electronegative atoms hold electrons more tightly, thus increasing the strength of the bond.