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# Mean Bond Enthalpy watch

1. How do you work it out.
Here is a question:
Mean bond enhalpy values/KJMol-1:
H-H=436
C=C=612
C-C=348
Use the following equation and data above to calculate the value for the C-H bond enthalpy in ethane?

Thanks for any help in Advance
2. (Original post by liquid394)
How do you work it out.
Here is a question:
Mean bond enhalpy values/KJMol-1:
H-H=436
C=C=612
C-C=348
Use the following equation and data above to calculate the value for the C-H bond enthalpy in ethane?

Thanks for any help in Advance
There appears not to be a following equation.
3. (Original post by joostan)
There appears not to be a following equation.
Ofcourse:

CHCH + H2 ---> CH3CH3 DeltaH=-136KJmol-1
4. (Original post by liquid394)
Ofcourse:

CHCH + H2 ---> CH3CH3 DeltaH=-136KJmol-1
This equation is not true. . .
5. (Original post by joostan)
This equation is not true. . .
Its what they gave in the book, I just want to work out what the Average enthalpy is for the C-H bond
6. (Original post by joostan)
This equation is not true. . .
In what way isn't the equation true?
Unless I'm missing something painfully obvious, they're just reducing ethene

Edit: On closer inspection, you might be right. Either we're missing some hydrogens, or there's a triple bond between the carbons
7. (Original post by Artymess)
In what way isn't the equation true?
Unless I'm missing something painfully obvious, they're just reducing ethene

Edit: On closer inspection, you might be right. Either we're missing some hydrogens, or there's a triple bond between the carbons
precisely
8. (Original post by Artymess)
In what way isn't the equation true?
Unless I'm missing something painfully obvious, they're just reducing ethene

Edit: On closer inspection, you might be right. Either we're missing some hydrogens, or there's a triple bond between the carbons

(Original post by joostan)
precisely
If I drew the displayed formulas for CHCH + H2 ---> CH3CH3

It would be:

H-C---C-H (triple bond) + H-H (single) -----> H3-C-C-H3 (single)
9. (Original post by liquid394)
If I drew the displayed formulas for CHCH + H2 ---> CH3CH3

It would be:

H-C---C-H (triple bond) + H-H (single) -----> H3-C-C-H3 (single)
There aren't enough Hydrogens on the left
10. you would need Delta H of a reaction involving the hydrogenation of ethene i believe to solve this not thought about it for long. you could then work out the bond breaking enthalpies reverse sign of foramation and the bonds formed and equate this to the overall delta H and do the maths, though i need pen and paper to show this and by the looks of it you dont have enough information.

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11. I think I've done this question!!!

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12. c2h4 + h2 = c2h6

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13. (Original post by joostan)
There aren't enough Hydrogens on the left

(Original post by alexandraa)
I think I've done this question!!!

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c2h4 + h2 = c2h6

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The overall equation is :

H-C=C-H + H-H ------------> H3C-CH3
Ethene + Hydrogen ---------> Ethane

DeltaH=-136Kjmol-1

Use the equation above and the bond enthalpies bonded above on 1st post to calculate a value for C-H bond enthalpy in ethane.
14. (Original post by liquid394)

The overall equation is :

H-C=C-H + H-H ------------> H3C-CH3
Ethene + Hydrogen ---------> Ethane

DeltaH=-136Kjmol-1

Use the equation above and the bond enthalpies bonded above on 1st post to calculate a value for C-H bond enthalpy in ethane.
I'd suggest writing it like this:
C=C + 2C-H + H-H ==> C-C + 6C-H
As DeltaH=-136Kjmol-1
You know that the difference between the bond enthalpies = delta H
15. (Original post by liquid394)

The overall equation is :

H-C=C-H + H-H ------------> H3C-CH3
Ethene + Hydrogen ---------> Ethane

DeltaH=-136Kjmol-1

Use the equation above and the bond enthalpies bonded above on 1st post to calculate a value for C-H bond enthalpy in ethane.
id hope so only got ch5 wjec left and on A.

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