| 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. |
