Bond enthalpies

[JulieAljamal1E]

On problem 4E.5 part a, it asks to calculate the reaction enthalpy using bond enthalpies for the reaction 3C2H2->C6H6
The table in the book gives what I’m assuming is a resonance bond enthalpy for benzene's Carbon single and double bonds. Before noticing that, I did 3(348)+3(612) which is for the single and double bonds of carbon, however this does not give me the same result as doing 6(518). Can someone please explain this?

[Elaine Pham 2E]

For this problem, I think you just have to know (by drawing its lewis structure) that benzene has resonance structures. That means all of its bonds are the same length, which is between the length of a single and double bond between carbons. So since benzene has 6 carbon-carbon bonds of the same length and not 3 carbon single bonds and 3 carbon double bonds, the bond enthalpy is different and you would use the bond enthalpy of 518 kJ/mol that's listed in the table.

[Eruchi Okpara 2E]

Are we expected to automatically know all the lewis structures/resonance structures in order to solve bond enthalpy problems?

[Sarah Bui 2L]

Are we expected to automatically know all the lewis structures/resonance structures in order to solve bond enthalpy problems?

I believe so since this was covered in Chem 14a and they wouldn't give the lewis structures to us on the test either.