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How do you calculate activation energy per vacancy?

  1. Apr 1, 2010 #1
    the question is like this:
    Calculate the activation energy needed to create a single vacancy in aluminium, given:
    T= 500 Celsius
    Density (500 Celsius) = 2.62 gr/cm3
    n = 7.57e23 m-3
    Mw (Al) = 26.98 gr/mol

    I know these Formulas:
    n = N*exp (Q/kT) (k = boltzmann's constant)
    N = Na*Density/Mw (Na = avogardo's number)
  2. jcsd
  3. Apr 1, 2010 #2


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    Hey ENgez, welcome to PF :smile:

    It seems like a direct question with a direct answer, just find Q [the activation energy required to create one vacancy].
  4. Apr 2, 2010 #3
    I did Find Q and it turned out to be 1.053 ev/mole or 16.85e-20 Joule/mole, but according to the answer sheet its supposed to be 72.33 kJoule/mole. Is it possible for the answer to be so big or is there a mistake in the sheet? And if there isn't, what am i doing wrong?

    Btw, thanks drizzle :)
  5. Apr 2, 2010 #4


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    An energy value like 1.053 ev, should be on the basis of an atom.
  6. Apr 2, 2010 #5


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    Gold Member

    Did you convert Celsius to kelvin?
  7. Apr 2, 2010 #6
    I solved it :). Thank you Astronuc and drizzle. Astronuc, your post made me see that i had actually found the energy per atom, so all i had to do was to multiply it by avagardo's number to get it per mole.
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