Chemistry - Thermochemistry Question with Solution | TestHub
Which of the following molecules will have different values of standard molar enthalpy of formation, one calculated using bond energy concept and other calculated calorimetrically? (one or more than one correct)
Options:(select one or more)
Answer:
Solution:
The bond-energy method assumes localized bonds with fixed average energies. This method disagrees with the calorimetric value when a molecule exhibits resonance or conjugation, as the extra stabilization energy is not accounted for. For example, 1,3-butadiene has conjugated double bonds (resonance), and N₂O is a resonance hybrid.
In contrast, C₂H₆ and 1,4-cyclohexadiene (which has isolated double bonds) do not exhibit delocalization. Therefore, for these molecules, both the bond-energy method and calorimetric values are in agreement. The correct answers are (b) and (d).
