Nuclear Fission Basics: Calculating Energy Released U-235

[rojasharma]

calculate the amount of energy released in the fission of a U-235 nucleus.
http://www.dummies.com/WileyCDA/DummiesArticle/Nuclear-Fission-Basics.id-1669.html
Given:
Masses of the particles:
U-235 = 234.9993u
n=1.008
Ba=140.883u
Kr=91.905u

what i did was i used delta E=mc^2, where m is the mass of n...which is 1.008.. and i get 1.5x10^-10... why is this wrong?/

 

[mgb_phys]

The energy given off is the mass difference between the original U and the total of the decay products.

U235 = 234.9993
Ba+Kr+n=140.883+91.905+1.008 = 233.796
difference = 1.203 then just E=mc^2

 

[rojasharma]

thanks:)

 

[rojasharma]

delta E=1.795x10^-10J...is this answer correct?

 

[rojasharma]

i got it:)...the answer is 2.82x10^-11J.

 

[mgb_phys]

If you did the arithmetic correctly!
Typical U235 fission is around 200Mev or 3E-11J but depends on the exact breakup products
with U235->Ba + Kr you would normally get 2 'extra' neutrons so your free energy is only about 0.2u