1
$\begingroup$

We all know that $$\ce{2Na +2H2O(g)->2NaOH +H2}$$

The question is:
What is the mechanism (not the reason that sodium is more 'electropositive' or more reactive than hydrogen, as in this question; and not in liquid phase involving $\ce{H+}$, which is mentioned also in that question) of this reaction?

The question of why sodium reacts with water is a thermodynamics question, but the question of how is a kinetics / mechanistic question. It is known that solvated electrons are very stable in liquid ammonia, but in water they are more shortived. From experiments such as pulse radiolysis it is known that solvated electrons in water react with solavted protons to form hydrogen atoms which then can combine to form hydrogen gas. If at the surface of a lump of sodium in water we have electrons being cast off into the water then we will have a source of solvated electrons and also sodium cations.

But if a sodium surface is exposed to water vapour then the reaction will be different as we can have water moelcules on the surface rather than bulk water. What will the mechanism be under these conditions.

See A Non-Exploding Alkali Metal Drop on Water: From Blue Solvated Electrons to Bursting Molten Hydroxide, Dr. Philip E. Mason,Tillmann Buttersack,Prof. Sigurd Bauerecker,Prof. Pavel Jungwirth, 2016 https://doi.org/10.1002/anie.201605986

Is it the same as the following two reactions? If not, what's the difference? $$\ce{3Fe + 4H2O(g) ->[\Delta]Fe3O4 + 4H2}$$ $$\ce{Zr + 2 H2O(g) ->[\Delta]ZrO2 + 2 H2}$$

$\endgroup$
5
  • 1
    $\begingroup$ Note that element symbols in ch. reactions should be upright, using mhchem package ( \ce{} )// Useful links for text and formula formatting: Notation basics , Formatting of math/chem expressions and upright vs italic $\endgroup$
    – Poutnik
    May 9, 2022 at 6:37
  • 3
    $\begingroup$ Try something like this: $$\ce{2 Fe + 3 H2O(g) ->[\Delta]Fe2O3 + 3 H2}$$ $$\ce{2 Fe + 3 H2O(g) ->[\Delta]Fe2O3 + 3 H2}$$ $\endgroup$
    – Poutnik
    May 9, 2022 at 8:26
  • $\begingroup$ Related: chemistry.stackexchange.com/questions/132500/… $\endgroup$ May 9, 2022 at 12:20
  • $\begingroup$ Fe reacts with water to give Fe++ not Fe+++; Steam gives Fe3O4. It seems to get to Fe2O3 O2 is needed. $\endgroup$
    – jimchmst
    May 27, 2022 at 22:21
  • $\begingroup$ @jimchmst thanks for the correcting. $\endgroup$ Jun 18, 2022 at 13:13

1 Answer 1

2
$\begingroup$

Solvated electrons do not exist in gas phase. In the water vapor, the reaction is simply an electron transfer from the sodium atom $\ce{Na}$ to one of the $\ce{OH}$ bonds of the $\ce{H2O}$ molecule. Then it is then broken into an $\ce{H}$ atom and an $\ce{OH-}$ ion. Later on, two $\ce{H}$ atoms are joined to yield a $\ce{H2}$ molecule.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.