Question

What is actual difference between atomic hydrogen and nascent hydrogen?

Answer 1

Nascent hydrogen is an old term, outdated even, postulated to describe a "species" of atomic hydrogen gas that was produced in situ (on site), to claim that it is a "highly reactive" version of `"H"_2(g)` stored over a longer period of time.

(Really, it is just an overly-simplified explanation of why such "species" [which are not new to us] tend to be more reactive than bottled ones stored over time.)

`"Zn"(s) + "H"_2"SO"_4(aq) -> "ZnSO"_4(aq) + overbrace(2"H"(g))^"'Nascent Hydrogen'"`

This tends to be in the context of dissolving-metal reactions. Although I usually see this reaction forming `"H"_2(g)`, this process shown above is at around `4000 - 4500^@ "C"`, which promotes homolytic cleavage of `"H"_2` into `2"H"`.

(These days, we know that of course it's more reactive than `"H"_2(g)`... `"H"cdot` is a radical!)

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Atomic hydrogen is more generalized, and is simply the `"H"` atom, one proton plus one electron.

`"H"_2(g) + "436 kJ" -> 2"H"(g)`

This is just in general, and out of context of dissolving-metal reactions. I don't think we use the term "nascent hydrogen" anymore...