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Heat generated

  1. Nov 9, 2016 #1
    1. The problem statement, all variables and given/known data
    The heat of combustion of graphite and that of CO is 394kJ/mol and 283 kJ/mol, respectively. When 12g of graphite is combusted incompletely, the same volume of CO and CO2 are generated. Calculate the heat of generated by this combustion. Choose the closet value.(kJ)
    A.197 B.253 C.308 D.339 E.505 F.677

    2. Relevant equations
    The answer is B.253kJ
    3. The attempt at a solution
    My idea is:
    ##C+O2→CO\\
    1 \qquad \qquad 1## and ##ΔH_1=-394kJ/mol##
    ##CO+O2→CO2\\
    0,5 \qquad \qquad 0,5## and ##ΔH_2=-0,5.283 kJ/mol##
    So ##ΔH=ΔH_1+ΔH_2=-535,5kJ/mol##
    Where is my wrong?
    Thanks for helping
     
  2. jcsd
  3. Nov 9, 2016 #2

    Bystander

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    Wrong.
    Ask yourself, "How many moles of carbon have been burned? How many moles of gaseous products have been formed? What is the minimum heat?"
     
  4. Nov 9, 2016 #3
    I think 0,5 mol CO and 0,5 mol CO2 are generated and 1 mol C is combusted
     
  5. Nov 9, 2016 #4

    Bystander

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    Correct. And the minimum heat released is what?
     
  6. Nov 9, 2016 #5
    I don't know.
    ##C+O2→CO\\
    1 \qquad \qquad 1## and ##ΔH_1=-394kJ/mol##
    ##CO+O2→CO2\\
    0,5 \qquad \qquad 0,5## and ##ΔH_2=-0,5.283 kJ/mol##
    So ##ΔH=ΔH_1+ΔH_2=-535,5kJ/mol##
    1 mol of C is combusted and 0,5 mol of CO and CO2 are generated . So the heat is -535,5kJ/mol?
     
  7. Nov 9, 2016 #6

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    What's half a mol x 394 kJ/mol?
     
  8. Nov 10, 2016 #7
    197kJ/mol
    but 1 mol C is burned, not 0,5 mol. And 1mol CO is generated but 0,5 mol CO is burned and 0,5 mol CO2 is generated.
     
  9. Nov 10, 2016 #8

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    Yes, and ....
     
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