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At the surface of Venus, at a pressure of 93 bar and a temperature of 737 K, both carbon dioxide and nitrogen are supercritical fluids.

Now, supercritical $\ce{CO2}$ is used as a solvent in processes such as decaffeination of coffee beans. But is it possible that the supercritical $\ce{CO2}$ on the surface of Venus could support more complex chemical reactions by dissolving substances, mixing them, and promoting reactions between them? Is it possible for supercritical $\ce{CO2}$ to play a similar role to what water does on Earth?

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    $\begingroup$ What you are missing is that supercritical fluid can be "gas-like" or "liquid-like". Liquid-like CO2 is used for extraction, but in such high temperature it would be gaslike, similar to the one you're breathing. You'd need way more pressure to make CO2 that hot, to be liquid-like. $\endgroup$
    – Mithoron
    Nov 24, 2021 at 0:04
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    $\begingroup$ ... and acidic fumes of sulphuric acid. $\endgroup$
    – Poutnik
    Nov 24, 2021 at 8:39
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    $\begingroup$ @Greg Most of "permanent gases " are at room temperature supercritical fluids. At low pressure, their properties converge to properties of ideal gas. At high pressure, their (at least some) properties converge to properties of liquids. All without any sudden phase change. Imagine if you had a vapor, being progressively pressurized and progressively becoming a liquid, without any condensation. $\endgroup$
    – Poutnik
    Nov 25, 2021 at 8:44
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    $\begingroup$ Sure those lines have no physical meaning just nomenclature one. Supercritical CO2 used for some extractions does not principally differ from supercritical nitrogen, if pressurized to comparable densities. The truth is, if T is much higher than Tc, we can practically forget it is still in supercritical region and consider is as permenent, near ideal gas. $\endgroup$
    – Poutnik
    Nov 25, 2021 at 12:56
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    $\begingroup$ It is better to denote the respective regions as liquid phase, gaseous phase and supercritical phase, with the latter being neither of the former two and having continuous convergence to both. $\endgroup$
    – Poutnik
    Nov 25, 2021 at 13:02

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If your key question is just the solvation ability of supercritical carbon dioxide and nitrogen for biogenic reactions, keep in mind that pure supercritical carbon dioxide is a very poor solvent. It is close to a solvent like pentane. I am sure supercritical nitrogen would be even worse solvent for polar compounds. The beauty of supercritical fluids is that their solvation ability depends on the density as well. Higher the pressure, better is their solvation ability in general.

Those who do supercritical fluid chromatography with carbon dioxide know that most bio-molecules / amino acids/ nucleic acids/sugars etc. are not soluble in such a system. Secondly, supercritical carbon dioxide is not miscible with water, you have to add small amount of alcohols to allow some water with pressurized carbon dioxide, in that case it is no longer a supercritical fluid.

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    $\begingroup$ Thank you. I think you understood the question perfectly, and it looks like the answer is not what I hoped it would be, and also more complicated than I thought it was. And, whoever edited the title, it does look a little classier now. $\endgroup$
    – Greg
    Nov 24, 2021 at 18:24

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