Bonding Enthalpies

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Kelsey Jug 1J
Posts: 38
Joined: Wed Sep 21, 2016 2:59 pm

Bonding Enthalpies

Postby Kelsey Jug 1J » Wed Jan 11, 2017 3:38 pm

For some clarification of the example in the course reader about enthalpies of bonds breaking (involving C-C, C-H, and C-Br bonds), is it correct that we have to account for the formation of the C-C single bond because the C=C breaks completely before it forms a single bond, rather than just jumping from a double to a single bond?

Sarah_Heesacker_3B
Posts: 21
Joined: Wed Sep 21, 2016 2:57 pm

Re: Bonding Enthalpies

Postby Sarah_Heesacker_3B » Wed Jan 11, 2017 4:35 pm

I believe so! You can check by comparing the values of the bond enthalpies used in the example in the course reader to the values in Table 8.7 in the textbook. Based on these values used, the C=C double bond does break completely (612 kJ/mol) and then a C-C single bond forms (-348 kJ/mol).
Hope this helps!

Julia Nakamura 2D
Posts: 33
Joined: Wed Sep 21, 2016 2:57 pm

Re: Bonding Enthalpies

Postby Julia Nakamura 2D » Wed Jan 11, 2017 4:36 pm

Yes, the carbon-carbon double bond is broken completely, and we do not measure the double bond break as a single bond break. This also means that the single bond formed between the carbons is considered a brand new bond.

So, the enthalpy of the double bond that was broken (between the two carbons) would be added to the equation since it requires energy to break the bonds. The enthalpy of the new bond formed (carbon-carbon single bond) will subtracted from the total enthalpy since it is a release of energy when the new bond is formed.

Hope this helps!


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