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4E.9

Posted: Tue Feb 04, 2020 5:33 pm
by Gabriella Bates 2L
Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene.

When we calculate the molar energy without resonance, we get 2880 kJ, and when we calculate the molar energy with resonance, we get 3108 kJ. This is higher energy, so why is it more stable? Thanks in advance

Re: 4E.9

Posted: Tue Feb 04, 2020 7:55 pm
by Emily Chirila 2E
I was stuck on this question too. Can someone explain the difference/relationship between molar energy and stability of a molecule? Is it referring to the energy required to break the bonds so having a higher molar energy means it is less likely to be broken?

Re: 4E.9

Posted: Tue Feb 04, 2020 9:18 pm
by Kaitlyn Ang 1J
Gabriella Bates 2L wrote:Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene.

When we calculate the molar energy without resonance, we get 2880 kJ, and when we calculate the molar energy with resonance, we get 3108 kJ. This is higher energy, so why is it more stable? Thanks in advance


How did you get that the molar energy without resonance is 2880kJ?

Re: 4E.9

Posted: Wed Feb 05, 2020 12:56 am
by 705121606
Kaitlyn Ang 1J wrote:
Gabriella Bates 2L wrote:Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene.

When we calculate the molar energy without resonance, we get 2880 kJ, and when we calculate the molar energy with resonance, we get 3108 kJ. This is higher energy, so why is it more stable? Thanks in advance


How did you get that the molar energy without resonance is 2880kJ?


You have 3 double carbon bonds + 3 single carbon bonds:
3(348KJ) + 3(612KJ) = 2880 KJ

Re: 4E.9

Posted: Wed Feb 05, 2020 12:57 am
by 705121606
I am also confused on this because I thought because resonance had a higher enthalpy, more heat was absorbed making it a higher energy state and therefore less stable? Someone please explain

Re: 4E.9

Posted: Wed Feb 05, 2020 1:01 am
by 705121606
I found this endorsed answer on chemistry community:
"The kekule structure of benzene suggests alternating single and double bonds, whereas the resonance structure contains six bonds that are between a single and double bond. The resonance structure is more stable, as all six bonds between the carbon molecules are the same"

Re: 4E.9

Posted: Wed Feb 12, 2020 7:31 am
by Elizabeth Bowen 1J
I found this answer from chem community to be helpful: "In order to do this problem, you would first calculate the energies to break the bonds of 3 double bonded carbons and 3 single bonded carbons. You would then compare this value to 6 resonance carbon bonds, and see that the resonance structure requires more energy to break the bonds, and it is therefore more stable." If a molecule has a higher H value from its bond enthalpies, it's more stable, bc it requires more energy to break the bond, so the molecule is more likely to stay in the formation it is already in and not react.