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Homework Help: Nuclear Fission of 1g of Uranium 235

  1. Nov 7, 2011 #1
    1. The problem statement, all variables and given/known data

    What is the amount of energy released when 1g of uranium 235 undergoes fission? Fission of uranium is: uranium + n -> Ba + Kr +12n.

    2. Relevant equations


    3. The attempt at a solution

    I found the mass of the reactants to be 236.05256u and the products to be 235.92392u.
    Thus Δm=-0.12864u

    There are 2.56207x10^21 nuclei in 1g.

    Therefore the energy needed is -165.122 J/g using E=Δmc^2. Is this the correct answer?
  2. jcsd
  3. Nov 8, 2011 #2
    You need to convert the Δm into kg using the information that 1u = 1.66 x 10^-27kg
    Then use E = mc^2 with this mass in kg (c = speed of light 3 x 10^8m/s)
    This is the energy released by each fission of U235.
    Multiply by the number of nuclei undergoing fission.
  4. Nov 8, 2011 #3
    Sorry clicked submit. Look below
    Last edited: Nov 8, 2011
  5. Nov 8, 2011 #4
    I did convert u to kg. I got -165.122 J/g, which I think is really low for Uranium. Can you check my answer? Is my change in mass right?
  6. Nov 8, 2011 #5
    Your Δm =0.12864u when converted to kg becomes 0.12864 x 1.66 x 10^-27 kg
    =2.14 x 10^-28kg. This is the mass to use in E = mc^2
    This is the energy released in 1 fission.
    For 1g of material multiply by the number of atoms in 1g (I agree with the number you got)
    When I did the calculation I got 49.2J
    Last edited: Nov 8, 2011
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