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Chemistry SE Question: Starting with a gas mixture of some combination of gases containing carbon and oxygen with a total carbon atomic fraction $f$, would it always reach the same equilibrium proportions of $\ce{CO2 + O2 + CO}$?

For example if I had an equal number of $\ce{CO2}$ and $\ce{O2}$ molecules then $f=0.2$, but so would two molecules of $\ce{CO2}$ for every three molecules of $\ce{O2}$. If I started with either mixture in this example, would I end up with the same equilibrium mixture of $\ce{CO2}$ and $\ce{CO}$ and $\ce{O2}$?

Simplifying assumptions: Assume $\pu{273K}$ and $\pu{610Pa}$ if necessary, the answer may be as simple as "yes it would" or "no it wouldn't, because...", a supply of ionizing radiation from space (hard UV and energetic cosmic ray particles) and a billion years, and ignore transmutation of elements by those particles.


Background and motivation is from my Space Exploration SE question Are Mars' atmospheric CO₂, O₂ and CO in equilibrium? Are sunlight or chemical reactions involved?, which begins:

According to the NASA JPL video linked below the top five gases comprising the martian atmosphere include $\ce{CO₂, O₂}$ and $\ce{CO}$. Do the proportions reflect some chemical equilibrium? Are sunlight or chemical reactions involved in maintaining these proportions?

Component     Fraction
   CO2          95.9%
   Ar            2.0%
   N2            1.9%
   O2            0.14%
   CO            0.06%

The NASA JPL video Crazy Engineering: Making Oxygen on Mars with MOXIE is linked in How many square meters of solar panel to power a MOXIE-like oxygen source per person?.

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  • $\begingroup$ I'm guessing that the answer is "yes it would" but I'm not a chemist. $\endgroup$ – uhoh Jan 28 '20 at 13:39
  • $\begingroup$ As soon as the mixture is allowed to reach equilibrium in the first place, yes. (I guess a billion years is quite enough.) Short of that, no. $\endgroup$ – Ivan Neretin Jan 28 '20 at 13:45
  • $\begingroup$ Obviously not, because mars rotates and has a climate, with seasons. ;) $\endgroup$ – Karl Jan 28 '20 at 18:24
  • $\begingroup$ @SurArthur7 thanks for the edit! I've never seen \pu{} used before but it looks great. I didn't find it in this tutorial so I'm wondering 1) what it's called, and 2) if it should be added there somewhere? $\endgroup$ – uhoh Jan 29 '20 at 0:14
  • $\begingroup$ @Karl this question is not about Mars. That was included as "Background and motivation" but for this question in Chemistry SE I've stipulated a constant temperature and pressure for this gas mixture. $\endgroup$ – uhoh Jan 29 '20 at 0:24

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