Where does the mass to energy conversion take place?

Question

As I understand, the nuclear bomb "little boy" detonated over Hiroshima converted about the mass of a paper clip into energy during the explosion. Now, as far as I understand what was going on, uranium 235 atoms were exposed to californium, an element whose radiation takes the form of neutrons. The neutrons smashed into the uranium 235 atoms, causing fission, and a chain reaction because after one atom was split it would make all the atoms around it split, et cetera. However, in all the explanations I have seen for this, there was never anything about where mass --> energy conversion happened. There is no account for particular neutrons turning into energy, and I would like to know where and when that happened. I know little about the topic, but I thought maybe it happened when a neutron got a "head on collision" with another neutron, but of course that would lead you to assume a lot more than the mass of a paper clip turning into energy, as the bomb was a couple tons in weight. On a broader note, I would just like to know where this mass --> energy conversion happens in everyday (or every other day) reactions such as sodium and water, baking soda and vinegar, mentos and coke, Thermite, Nuclear Fusion (like in our sun) etc. Once again, I would like to know where and when mass is converted into energy in the above. Thank you.

 

-- George 

Answer 1

In nuclear fission, a neutron is fired into a U-235 atom creating a U-236 atom. U236 is unstable and immediately decays into atoms of Ba-141 (barium), Kr-92 (krypton), three neutrons, and energy.  U236 has an atomic mass of 236.05. The combined mass of the decay products total 233.85. The mass difference (2.20) is converted to energy per E = mc².

Einstein's equation E=mc2 tells us that mass and energy are the same thing - it's all really just energy.  The "mass" of U236 includes the nuclear binding energy - that is, when you "weigh" a nucleus, the binding energy contributes to the weight.  When you break the U236 apart, some of that binding energy is released.  Why?  Because the smaller atoms each have fewer protons in the nucleus, so less energy is needed to hold the nucleus together.  Hence the "mass" of the decay products is less than the mass of the U236.

 

Everyday reactions like vinegar and baking soda or mentos and coke are chemical reactions, not nuclear ones.  They involve interactions of the electrons of atoms.  The nucleii are unaffected by chemical reactions.  In truth, some "mass" is converted into energy in chemical reactions as well, but the amount is infinitesmally small and is not readily detectable.