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Hess's Law

  1. Feb 15, 2004 #1
    The enthalpy of combustion of solid carbon to form carbon dioxide is -393.7 kj/mol carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is -283.3 kj/mol CO. Use these data to calculate change of enthalpy for the reaction

    2C(s) + O2(g) -> 2CO(g)

    ----------------------

    I'm quite lost . . . after trying this problem for about 20 mins now . . . I still don't see how to use Hess's Law to formulate this answer

    What i tried to do was to "form" the equations by the words in the problems.

    He are my formulations below; however, I can't seem to get the equation mentioned above.

    2CO + O2 -> 2CO2
    C + O2 -> CO2

    when I rearrange these . . . I can't seem to get 2C(s) + O2(g) -> 2CO(g)

    the answer is -220 Kj/mol

    thanks
     
    Last edited: Feb 15, 2004
  2. jcsd
  3. Feb 15, 2004 #2
    RE: EUREKA!!!

    EUREKA!!! I GOT IT :) :)

    2 (C + O2 -> CO2) change in Enthalpy = 2(-394) kj/mol
    2CO2 -> O2 + 2CO change in Enthalpy = 2(239.3) kj/mol

    = 2C + O2 -> 2CO change in Enthalpy = 221 kj/mol + or - 1 kj/mol

    :D ;) :)
     
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