Calculating Energy Released in a Fission Reaction: Where Did I Go Wrong?

AI Thread Summary
The discussion revolves around calculating the energy released in a fission reaction, specifically involving U-235. The initial calculation mistakenly resulted in 1.15 x 10^12 J instead of the correct 1.15 x 10^9 J, indicating an error by a factor of 1000. Participants clarify that the mass should be in kilograms, not grams, and emphasize the importance of using Avogadro's number to determine the number of U-235 atoms per kilogram. The correct steps involve calculating the number of atoms in 2 kg of uranium fuel and converting the energy from MeV to Joules accurately. The final consensus suggests that the initial quoted answer may be incorrect, prompting further verification.
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Homework Statement
Calculate the amount of energy, in joules, generated from 2 kg of uranium fuel, if the U-235 represents 0.7% of the metal and every fission reaction produces 200 MeV.
Relevant Equations
E = mc^2
Energy = ##\frac{2000}{235}## x 6.02 x 1023 x 0.7% x 200 x 1 x 106 x 1.6 x 10-19 = 1.15 x 1012 J

But the answer is 1.15 x 109 J

I am off by a factor of 1000. Where is my mistake?

Thanks
 
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SI units for mass is kg not g
 
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malawi_glenn said:
SI units for mass is kg not g
Sorry I don't understand the hint.

Wouldn't it be the same if I write: ##\frac{2}{0.235}## instead of ##\frac{2000}{235}##?
 
And I don't understand your solution, it is just a bunch of numbers.

Anyway, do it in steps. First, how many U-235 atoms are there per kg?
 
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malawi_glenn said:
And I don't understand your solution, it is just a bunch of numbers.

Anyway, do it in steps. First, how many U-235 atoms are there per kg?
Let me redo

1) No. of atoms of U-235 in 2 kg of uranium fuel = ##\frac{2000}{235}## x 6.02 x 1023 x 0.7% = 3.586 x 1022 atoms

2) Amount of energy released = 200 MeV x No. of atoms = 7.127 x 1024 MeV

3) Convert MeV to Joule = 7.127 x 1024 x 1 x 106 x 1.6 x 10-19 = 1.15 x 1012 J

Thanks
 
And 6.02 x 1023 is avogadros number, the number of entities in one mol.
U-235 is approx 235g / mol.

Anyway, the answer you quoted is most likely wrong.
 
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Thank you very much malawi_glenn
 
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