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I'm trying to get a grasp of the power within a single hydrogen atom (e.g. the power released when whatever process happens in a hydrogen bomb)... If we could enlarge a hydrogen atom up to the size of your fist, how much energy would it give off?

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Perhaps you'd be better off talking about a mass of hydrogen the size of your fist, the energy output of that hydrogen bomb, and then dividing that by the number of atoms you started with. To first approximation, this would be something like: $\frac{1}{4}\left(4\,m_{H} - m_{He}\right)c^{2}=\left(1.00794 u - 0.25*4.002602 u \right)*931.46 \frac{MeV}{u}=6.790 MeV$ – Jerry Schirmer Mar 11 '11 at 15:15
This comes less than a day after How much energy can be extracted from hydrogen? which seems to share some of the same confusion. – dmckee Mar 11 '11 at 16:31

One can not build a hydrogen bomb with a single hydrogen atom since it requires fusion of more than one nuclei. Neither one can "enlarge" a hydrogen atom. An atom of hydrogen is made of one electron and one proton. There are certain specific orbitals around the nucleus whose sizes are fixed. One just can not rescale it. The size of any atom is fixed by fundamental physical constants. The energy of the hydrogen bomb comes from fusion of hydrogen atoms to form helium atoms. The final mass of the system is less than the initial mass and the lost mass is converted to energy by the equation $E = mc^2$ where $m$ is the mass difference.

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