# Does high pressure reverse reaction between zinc and sulfuric acid?

When zinc is added to sulfuric acid, it undergoes a chemical reaction that generates hydrogen gas and zinc sulfate. Can this reaction be reversed by applying pressure to the products converting them back into zinc and sulfuric acid?

$$\ce{Zn(s) + H2SO4(aq) <=> ZnSO4(aq) + H2(g)}$$

Are there any sources claiming this reaction can be controlled by pressure at all?

• It should even be possible to get a very crude estimate for what kind of pressure would be needed by assuming that the pressure dependence of the Gibbs free energy of reaction is solely due to the hydrogen gas (while also assuming it's an ideal gas), and then figuring out at what pressure the reaction free energy reaches zero. As Poutnik mentions, it'll be very high, probably tens of thousands of atmospheres at least. Mar 4 at 6:39
• A classical example for this is Fe. For zinc the enthalpy is too big. Mar 4 at 18:12
• And there's another, more immediate, issue: why would it reduce Zn and not sulfur? Mar 4 at 18:20
• I am new to chemistry and found out this suggestion using chatgpt. We could say it was his idea. Mar 5 at 13:41
• It's a chatbot so it has no ideas. Just rips off of stuff it found and pretends to be someone. Mar 6 at 0:54

As a very rough estimation of pressure when the hydrogen redox potential equals zinc standard redox potential, we can use the extrapolation of the Nernst equation:

\begin{align} E^\circ_\ce{Zn/Zn^2+} &= E^\circ_\ce{H2/H+} + \frac{\pu{0.059 V}}{2} \log\left(\frac{[\ce{H+}]^2}{p_{\ce{H2}}}\right) \tag{1}\\ \log(p_\ce{H2}) &= \left(E^\circ_\ce{H2/H+} - E^\circ_\ce{Zn/Zn^2+}\right) \frac{2}{\pu{0.059 V}} \tag{2}\\ p_\ce{H2} &= 10^{\left(E^\circ_\ce{H2/H+} - E^\circ_\ce{Zn/Zn^2+}\right) \frac{2}{\pu{0.059 V}}} \tag{3}\\ &= \pu{10^{\frac{2\times\pu{0.76 V}}{\pu{0.059 V}}} atm} \\ &\approx \pu{5.8E25 atm} \end{align}

This extrapolating estimation is not realistic, being far out of validity scope of the Nernst equation. Even pressure many orders lower would make the system very different, everything solid, including hydrogen. $$\pu{E25 bar}$$ would cause an universal nuclear fusion. As Loong has noted, the Solar core pressure is $$\pu{2.5E11 bar}$$. If protons had been fusable directly like deuterium is…

But it gives the clear message the pressure cannot help in reaction reversal.

Any equilibrium calculation involving ordinary compounds that gives a pressure of $$10^5$$ bar or more is probably not realistic.

Chemical bonds can deform and rearrange under such pressures and thus create different compounds we would consider exotic. One example we have seen on this site involves "sodium chloride" in which the bonding rearrangement leads to stoichiometries other than the normally "obvious" $$\ce{NaCl}$$ .

Reference

1. Zhang, W.; Oganov, A. R.; Goncharov, A. F.; Zhu, Q.; Boulfelfel, S. E.; Lyakhov, A. O.; Stavrou, E.; Somayazulu, M.; Prakapenka, V. B.; Konôpková, Z. (2013). "Unexpected Stable Stoichiometries of Sodium Chlorides". Science. 342 (6165): 1502–1505. arXiv:1310.7674. Bibcode:2013Sci...342.1502Z. doi:10.1126/science.1244989. PMID 24357316. S2CID 15298372.