# Would the same equilibrium concentration of carbon dioxide, carbon monoxide and oxygen always result for a given initial atomic carbon fraction?

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%

• I'm guessing that the answer is "yes it would" but I'm not a chemist. – uhoh Jan 28 '20 at 13:39
• 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. – Ivan Neretin Jan 28 '20 at 13:45
• Obviously not, because mars rotates and has a climate, with seasons. ;) – Karl Jan 28 '20 at 18:24
• @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? – uhoh Jan 29 '20 at 0:14
• @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. – uhoh Jan 29 '20 at 0:24