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Homework Help: Heat of Atomization?

  1. Dec 1, 2017 #1
    1. The problem statement, all variables and given/known data
    So, my textbook doesn't go over these type of problems for heat of atomization , so im confused on how to write the chemical equations for them.

    Question: The heat of atomization is the heat needed to separated gaseous atoms from a substance in its standard state. The equation for the atomization of graphite is C(graphite) --> C(gas)
    2. Relevant equations
    Given,
    1) Heat of formation for CH4 = -74.9 Kj/mol
    2)Heat of atomization for CH4 = 1660 kj/mol
    3) heat of atomization for H2 = 423 kj/mol

    3. The attempt at a solution
    For the equation number 1, i got C(graphite) + 2H2 -> CH4(s)
    for number 2, i got C(graphite) + 4H -> C(g) + H(g)
    For 3, i got 1/2H2(g) --> H(g)

    I'm not sure if the second one is write. I was thinking that if i was able to write the equations correctly, then i can do some cancellation so i get C(graphite) --> C(gas).
     
  2. jcsd
  3. Dec 2, 2017 #2

    Borek

    User Avatar

    Staff: Mentor

    CH4 is not solid (check your first equation). In the second you should have just CH4(g) on the left, not some combination of separated elements.
     
  4. Dec 2, 2017 #3
    So it should look like this?

    C(graphite) + 2H2(g) -> CH4(g)
    CH4(g) -> C(g) + H(g)
    1/2H2(g) --> H(g)

    How would the kj/mol change for each equation? Would they remain the same?
     
  5. Dec 2, 2017 #4

    Borek

    User Avatar

    Staff: Mentor

    First two equations look OK, I think the last one should be doubled - it is about atomizing a molecule, not half of the molecule. But in general you should check what definition you were given, as these things are often ambiguous.
     
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