Formaldehyde, CH₂O is a pungent, colorless gas famous for its use to preserve tissues or cells. Using the bond dissociation energies and the ΔH°_f = 716.7 kJ/mol for C(g), estimate the value of ΔH°_f for CH₂O at 25.0°C. Explain why the value obtained is only an estimate. The literature value of ΔH°_f of CH₂O is –108.6 kJ/mol.
Average Bond Dissociation Energies: O=O: 498 kJ/mol, H–H: 436 kJ/mol, C–H: 410 kJ/mol, C=O: 732 kJ/mol

• A. ΔH°_f = –99 kJ/mol; The value obtained from the bond energies is an estimate because the bond energies are average values derived from several different compounds.
• B. ΔH°_f = +99 kJ/mol; The value obtained from the bond energies is an estimate because the bond energies are average values derived from several different compounds.
• C. ΔH°_f = –150 kJ/mol; The value obtained from the bond energies is an estimate because the bond energies are average values derived from several different compounds.
• D. ΔH°_f = +150 kJ/mol; The value obtained from the bond energies is an estimate because the bond energies are average values derived from several different compounds.

Answer: (C)