Bond Enthalpy and Resonance

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Bond Enthalpy and Resonance

Postby skyeblee2F » Tue Feb 12, 2019 4:13 pm

For part (d) of #8.67 (6th edition) the problem is the same as part (c) except we take into account resonance. I would've assumed that we use the average of the bond enthalpies for a C--C bond (348 kJ/mol) and C==C bond (612 kJ/mol) and multiply that by 6 moles rather than add up 3 of each. However, the solutions manual used (518 kJ/mol) and multiplied that by 6 moles, which is not the average of 348 and 612.

Where does the 518 come from? I may have just forgotten how resonance works in relation to bond enthalpies.

Also, is this likely to be important for the midterm?

josie 1C
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Joined: Fri Sep 28, 2018 12:19 am

Re: Bond Enthalpy and Resonance

Postby josie 1C » Tue Feb 12, 2019 4:22 pm

the carbon-carbon bonds are kind of in-between double and single bonds because of resonance, but there a specific bond enthalpy (518 kJ/mol) for carbon with a single bond and a dashed line on top, that represents the resonance of 3 C-C and 3 C=C bonds.

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