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2014-12-05T08:25:50+05:30

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It looks like the heat of formation values given are probably not right.

    2 C +  O2  =>  2 CO        Let us say  a fraction = 2x moles formed CO.
    C + O2    => CO2          Then    a fraction 1 - 2x  moles formed CO2.



We are initially given 1 mole (12 gms) of Carbon.  So 2x moles of C and x moles of O2 combine to get 2x moles of  CO.

   (1-2x) moles of C combines with 1-2x moles of O2 to give  (1-2x) moles of CO2.

    Total enthalpy change from both reactions
              = 2x * Hf(CO) + (1-2x) * Hf(CO2) - (x+1-2x) * Hf(O2) - (2x+1-2x) * Hf(C)
               = - 75 Kcal = - 75 * 4.18 KJ
     2x * (-110.5) kJ +  (1-2x) * (-393.5)  KJ - (1-x) * (0 )  KJ - (+1.88 ) KJ  = - 75 * 4.18 KJ
           x = 0.138

   Total moles of oxygen reacted =  1 -x  = 0.862
     Mass of oxygen reacted = 0.862 * 32 = 27.584 gm

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