Atomic & Nuclear Energy Units

The electron volt
(eV) an energy unit for atoms

But there are lots of atoms in a substance

Nuclear energy unit: 

Fission energy

A single electron, accelerated through a potential difference of one volt, gains a kinetic energy of 1 electron-volt (1 eV), which is a very tiny 0.000 000 000 000 000 000 016 joules.  But electrons are numerous. 

If 1 eV of energy is gained by one electron in each molecule of a mole of substance (such as 12 grams of carbon), the total energy is 96500 joules.  One eV for every atom in a kilogram of carbon results in a total energy of 8  million joules.  Burning one kilogram of coal yields about 30 MJ.  This shows that shows that the chemical energy of coal-burning yields about 4 eV per atom burned.

Nuclear energies are much higher.  Gamma-ray energies from nuclei range from a low of about 12,000 eV from tritium to over 1,000000 eV (1 MeV) for Cs-137.  Alpha particles from naturally decaying radium, thorium, uranium, and similar species, typically have 4 MeV of energy.

The energy released when an atom of uranium-235 of plutonium-239 fissions (either naturally or by having been induced) is about 200 MeV (200,000,000 eV), or about 50 million times the energy released in burning an atom of carbon.

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