fission/mass defect (1 Viewer)

[johnnydepp]

fission/mass defect - please help!

call me stupid, but how does fission produce energy? i thought binding energy was the result of mass defect, as in the mass of the constituents of an atom is always larger than the mass of the atom. so if you split an atom in two, you have to add energy rather get energy. so how on earth do we get energy from a fission reaction? i know there must be a fallacy in my argument, but for the life of me, i can't find it.

 

[johnnydepp]

bump

 

[helper]

Fission reactors do not end up with the fundamental particles, rather they end up with smaller atoms. If you calculate the mass of the reactants and products, there is a deficit between the two. This defecit is then released as energy.

 

[johnnydepp]

Fission reactors do not end up with the fundamental particles, rather they end up with smaller atoms. If you calculate the mass of the reactants and products, there is a deficit between the two. This defecit is then released as energy.

so what you're saying is that it's totally different from an atom undergoing beta decay right? if that's so then, i kinda get it...

thx btw

 

[helper]

With Beta decay, you are obtaining the energy from within the nucleon (neutron) that is breaking down.

With fusion, you are obtaining the energy from the rearrangement of the neucleus and the difference in binding energy due to this.

 

[johnnydepp]

With Beta decay, you are obtaining the energy from within the nucleon (neutron) that is breaking down.

With fusion, you are obtaining the energy from the rearrangement of the neucleus and the difference in binding energy due to this.

i totally get it now! it's just like chem with the bond breaking and bond making. you're a champ

 

[ashbashness]

Sure, both the initial atom and the product atoms have binding energy, but the critical thing is binding energy PER NUCLEON. In a fission reaction, atoms larger than iron (such as uranium) split into two or more product atoms, each with more binding energy per nucleon. Therefore more binding energy is present in the surrounding environment.

Pulling figures from my ass:
say 1 atom of uranium has 10 J of binding energy (ie a mass deficit of 10 Joules/c2 ie it weighs 10 J/c2 less than it should ie it takes 10 J to seperate the atom into its constituent nucleons.) It then splits into 2 atoms each with 6 J of binding energy.
So now the total system weighs 12 J/c2 less than it should - this mass is present in the form of energy. So this process generated 12J-10J=2 J of energy which goes to heat the water and turn the turbine etc.