Astronomy Answers
From the Astronomical Dictionary

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the electronvolt

An electronvolt is a very small amount of energy, namely the energy that is involved when an electron experience a electric potential difference of 1 volt. This energy corresponds to about 1.6 × 10⁻¹⁹ J. The symbol for electronvolt is eV. The amount of energy that is involved in a typical chemical reaction is of the order of a few eV. Because an eV is so small, the following multiples are also often used: keV (kiloelectronvolt = 1000 eV), MeV (megaelectronvolt = 1000 keV), and GeV (gigaelectronvolt = 1000 MeV). The mass of an electron corresponds to about 0.5 MeV of energy, and the mass of a proton with about 1 GeV of energy, so MeV and GeV are good units of energy for nuclear reactions.