Feynboy
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The answer is C. How would you work it out from this?
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Kian Stevens
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The answer is C. How would you work it out from this?
You could compare the formation enthalpies of both ethane and ethene. You could also compare the energy needed to break the bond between the two carbon atoms (atomise/sublimate, in other terms) compared to ethane. The reason why we're comparing this to ethane is because there's the option to use mean bond enthalpies.

Both of the above factors would change for both ethane and ethene, based on the double bond.
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username3718068
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The answer is C. How would you work it out from this?
(1)
2C(s) + 2H2(g) => CH2CH2(g)----:
: :
: : (3)
: (2)
: :
: : :
2C(g) + 2H2(g)-------------------------:

(1) = enthalpy of formation of ethene
(2) = enthalpy of sublimation of carbon
(3) = mean bond enthalpy of C-H, C-C

Its a hesses law cycle.
You can work out the bond enthalpy of C=C as
(1) = (2) + (3) + bond enthalpy of C=C
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