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drafterman t1_iy9f82p wrote

Two hydrogen atoms have less mass than one helium atom because helium atoms have neutrons in addition to protons while hydrogen atoms just have protons.

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geekpeeps t1_iy9gdbf wrote

And the two hydrogens (now a molecule) have more energy because of the intermolecular forces - as the hydrogens oscillate (kind of) their movement towards and away from one another is more energetic than the helium atom just on its own.

Edit: there is a quantum chemistry exercise in calculating the variations in energy between a hydrogen 2+ molecule (two protons sharing an electron) and 3D mapping the changes. It was much more difficult without the internet and digital graphing available nowdays.

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Any-Growth8158 t1_iy9h94s wrote

I'd assume that diatomic hydrogen having more energy than a helium atom is discounting the mass energy of the neutrons...

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geekpeeps t1_iy9jsss wrote

It’s about the interactions between the two as they move away and toward each other. Helium will have complete a electron shell and the nucleus is basically at rest. Hydrogen as (H - H) is stable but reactive. Helium is inert.

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Lewri t1_iy9nybs wrote

This answer is wrong. Deuterium and tritium are just as much hydrogen as protium is, and similarly helium includes helium-3 as well as helium-4. Further, deuterium has a mass of 2,014,101.777844 µu, while helium-4 has a mass of 4,002,603.254130 µu, so we can see that even when the number of protons and neutrons line up, the mass is not the same.

As you can see from the numbers I just posted, you and OP (u/TheLapisBee) are actually also backwards in that 2 ^(2)H atoms have more mass than 1 ^(4)He atom.

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TheLapisBee OP t1_iy9phip wrote

Oh wow! I was very much wrong... So where does this mass come from in the fusion process?

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Lewri t1_iy9qo7c wrote

>So where does this mass come from in the fusion process?

The product has less mass than the ingredients. Mass is being lost, not gained, so the question is where does the mass go.

The answer to where the mass goes is that it goes to the energy of the radiation being emitted.

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TheLapisBee OP t1_iy9r2n3 wrote

Ohhhh right, got a bit confused, thanks! Also how do u highlight what part of my comment you reply to?

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Lewri t1_iy9rv39 wrote

Depends if you're using markdown or the "Fancy Pants Editor". In Markdown you simply put a > at the start of the paragraph, like this:

>This is a quote

In the "Fancy Pants Editor" you have to select the quote block option through the GUI.

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drafterman t1_iy9pr6l wrote

Sans clarification/qualification, it is not unreasonable to treat hydrogen as hydrogen-1 and helium as helium-4.

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