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What causes rusting? Some sources say ferrous metals don't rust without being exposed to humidity or water, whole others say they do rust as long as there is oxygen present, just more slowly. Which is correct? For example, if a vehicle were left in a bunker for a very long time, such as 100k years, with it dry the entire time, would it rust? And if so, would the rusting completely destroy it?

Adam
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    Cite your sources. – Poutnik May 16 '23 at 07:08
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    You have been supposed to find the provided link before asking. // Review the guides Asking and How to ask. Not following the guidance may lead to lack of satisfying answers, misunderstanding, objections, question down-voting or even question closure. – Poutnik May 16 '23 at 18:16

1 Answers1

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$\Delta_\mathrm{f} G^\circ$ (free energies of formation) at $\pu{298.15 k}$ of $\ce{FeO}$ and $\ce{Fe2O3}$ are$^1$ $\pu{-101 5.227 kJ mol-1}$ and $\pu{-742.294 kJ mol-1}$, both negative, implying both these reactions are spontaneous at ambient conditions.

However, we wouldn't call it rusting, because rust is $\ce{Fe2O3.xH2O}$, the hydrated form of $\ce{Fe2O3}$. Thus, an $\ce{Fe}$ sample would corrode in an $\ce{O2}$ chamber but not rust. You may observe black/red powder which will be easily distinguishable from rust by examination of color.

References

  1. Thermodynamic Data of Pure Substances. Ihsan Barin, Gregor Platzki. Third edition. VCH Verlagsgesellschaft mbH, Weinheim (Federal Republic of Germany), VCH Publishers, Inc., New York, NY (USA)
ananta
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