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 o

Question

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)

TestHub · Accepted Answer

Bond energies assume localized bonds. When resonance is present, the real molecule is more stable than the localized-bond structure, so the bond-energy value of Δ f H differs from the calorimetric one. Benzene (resonance between Kekule forms), O 3 (two equivalent resonance structures) and CO 2 (O=C=O with contributions from polar structures, with C=O bonds shorter and stronger than the standard C=O value) all show this difference. Propane has only single bonds and no delocalization, so both methods agree. Ans (a),(c),(d).

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