ELI5. Why does nuclear fission cause so much energy for such a little mass.


(This may sound dumb and i think im just missing a basic piece of energy production) I know how nuclear fission works, neutrons are fired as a nucleus which produces a unstable nucleus that then splits into 2 product nuclei and a select number of neutrons and releases an amount of energy (ie. U 235 -> u 236 -> Ba141 + kr92 + 3 neutrons + Q) but why is Q (energy) produced.
Mass is maintained so I don’t see why it needs to release energy especially one so disproportionate to its mass. Is it the break of the strong nuclear force that causes such a large energy output ?

In: 1

Simply put, there’s a TON of energy in mass. I’m face, that’s what E = mc^2 comes from.
And when c is the speed of light, energy gets huge for even tiny amounts of energy.

Also remember that there’s not just one atom undergoing this process. There are millions if not hundreds of billions of this process going on at the same time.

I never liked the E=mc^2 explanation because while it’s technically true it’s misleading because no protons nor neutrons are destroyed in fission.

The better reason is that in the nuclear core you have two forces, the strong nuclear force and the electromagnetic force. The strong force is super strong over a very very small distance, if this distance is exceeded, the electric forces are far stronger and cause the protons/atoms to push apart from each other.

Basically all we have to do is add a little bit of energy to the nucleus to destabilize it.


Mass is converted directly into energy.

Depending on the mass of matter that is converted, that can be quite a bit.

For reference, the Hiroshima and Nagasaki bombs converted about 1 gram (one US dime) of mass for about 1kg of U235 that went critical out of about 65kg of nuclear fuel.

Mass is in fact not maintained:

U236 has a mass of about 236.045568 u, Ba141 has 140.991411 u, Kr91 has 91.926156 u and a neutron has 1.008665 u.

If you subtract the masses of the barium, the krypton and the three neutrons from the mass of the uranium you got a leftover mass of 0.179006 u. Thats Q.