Final answer:
The strength of a C-C triple bond is not three times that of a C-C single bond because while the sigma bond in the triple bond contributes significant strength due to greater orbital overlap, additional pi bonds are weaker and contribute less to the overall bond energy.
Step-by-step explanation:
The strength of a carbon-carbon (C-C) triple bond is not three times that of a C-C single bond due to the nature of bonding interactions and orbital overlap. A C-C single bond is a sigma (σ) bond, formed by the end-on overlap of orbitals, which allows for a greater degree of overlap and thus a stronger bond. When double and triple bonds form, they include one σ bond but also pi (π) bonds, which result from the side-on overlap of p orbitals and are generally weaker than σ bonds due to less effective orbital overlap. This is why the increase in bond energy is not proportional to the number of bonds; the average bond energy of a C-C double bond increases by 267 kJ/mol from a single bond, and a triple bond increases by only an additional 225 kJ/mol, rather than doubling or tripling the single bond energy.
Comparing bond energies, the bond energy for a C-C single bond is 347 kJ/mol, and the bond energy for a C-C triple bond is 839 kJ/mol. This demonstrates that although triple bonds are stronger and shorter than single bonds, the cumulative strength of a triple bond is not simply three times the strength of a single bond because each additional π bond contributes less to the overall bond energy than the initial σ bond.