42 says consider the decomposition of liquid benze...

42 says consider the decomposition of liquid benzene togaseous acetylene. (My problem is actually #46 in the 10th editionbut cramster only has edition 9)

a) What is the enthalpy change for the reverse reaction
b) what is the deltha H for the formation of 1 mole ofacetylene?

In trying to find the enthalpy change of the reverse reaction Ikeep getting different answers than what was posted.
1. Since it is just a reverse reaction shouldn't it justbe a sign change from +630kJ to -630jK?
2. If the total delta H for 3 moles of acetelyne is630kJ if I needed the delta H for one mole of acetelyne wouldn't Ijust divide by 3 to get -210jK?
We reviewed this in class and the answer is different thanwhat was posted on cramster as being the answer for 42E.
Thanks for your help

Answers ( 1 )

  1. mason patel
    mason patel
    In ch 5 - 42E it is given
             1/3 C6H6 (l)= C2H2(g)   delta H = +210KJ
    a) for the reverse reaction its just the opposite-210KJ
    b) but for 1mol C2H2 formation, calculate delta H
                                = +210KJ / (1/3)mol * 1mol
                                = +630KJ
    since in the given reaction value is gven for 1/3mol
    I think the 46E is slightly different from 42E if deltaH is given for 3mol C2H2 & u have to find for 1mol then divide+630 by 3 and ans for reverse reaction will be
    =630KJ.
    If U still have problem, please post thequestion 10th edition.

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