(We must include electrons
in this calculation because 4.0026 amu is the mass of the
helium-4 atom, not the nucleus.) This missing mass corresponds
to 0.0305 x 931.4 MeV = 28.4 MeV of energy. If we could put
together a helium atom directly from two neutrons, two protons,
and two electrons, then 28.4 MeV of energy would be given
off for every atom formed:
      
   

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Compared to common chemical
reactions, this is an enormous quantity of energy. Since 1
electron volt per atom is equivalent to 23.06 kcal per mole,
   =
655,000,000 kcal mole-1
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