Sublimation of Carbon with Resonance

[Mika Sonnleitner 1A]

Question 8.67 asks to find the enthalpy of formation for benzene with and without resonance; how would you differentiate between the two? The problem only gives the chemical compound, so how would we know which chemical equation to use? For example, part (b) of this question asks to estimate the enthalpy of formation of methanol, and the next step in the solutions manual is to write the balanced chemical equation. How is this equation determined? Thanks.

[Curtis Tam 1J]

For benzene without resonance, you would use a bond enthalpy for C single bonded to C and a bond enthalpy for C double bonded to C. However, with resonance, you have a blend of both single and double bond character which means realistically you wouldn't use two distinct enthalpy values for C C bonds. The table should give an enthalpy value for C C bonds in benzene with resonance.

Enthalpy of formation is basically the amount of energy needed to create a mole of a specific substance from the most stable elements. Benzene is made of carbon and hydrogen so carbon as its most stable form would be C(graphite) and hydrogen in its most stable form would be H2(gas). For methanol, its the same in addition to O2(gas).

Hope that helps! :)