# Equilibrium Constants for Diatomic Gases at High Temperatures

I'm new here and I haven't taken chemistry beyond high school, so please forgive the ignorance. I am reading a book about hypersonic aerodynamics, and I am trying to connect some chemistry knowledge into my reading. I have four reactions listed in my book:

\begin{align} \ce{O2 &-> 2 O} &\quad (\pu{2000K} < T < \pu{4000K})\\ \ce{N2 &-> 2 N} &\quad (\pu{4000K} < T < \pu{9000K})\\ \ce{N &-> N+ + e-} &\quad (T > \pu{9000K})\\ \ce{O &-> O+ + e-} &\quad (T > \pu{9000K}) \end{align}

Now, the book doesn't go into the chemistry here really at all. I know that some minor dissociation happens at cooler temperatures, and there will still be some diatomic oxygen/nitrogen at higher temperatures too. But I'm trying to answer for myself just how much is around at those temperatures, and how much they change in the ranges that they list. Assuming I remember correctly, I need the dissociation constants for this. However, I'm having trouble finding them.

NIST chemical reaction searching tool doesn't seem to have the information I'm looking for, and Wolfram|Alpha (which generally helps) is not understanding what I'm trying to tell it… so I'm at a loss. My chemical engineer family member mentioned I could find it in the CRC Handbook of Chemistry and Physics, but unfortunately we can't seem to find our copy. My chemistry-major friend in college knew that it was possible to get the numbers, but he couldn't quite remember where I should start.

Either way, I'm looking for the equilibrium coefficients of:

$$\begin{array}{clr} \hline \# &\text{Reaction} & T/\pu{K} \\ \hline 1 & \ce{O2 -> 2O} & 2000 \\ 2 & \ce{O2 -> 2O} & 4000 \\ 3 & \ce{N2 -> 2N} & 4000 \\ 4 & \ce{N2 -> 2N} & 9000 \\ 5 & \ce{N -> N+ + e-} & 9000 \\ 6 & \ce{N -> N+ + e-} & 11000 \\ 7 & \ce{O -> O+ + e-} & 9000 \\ 8 & \ce{O -> O+ + e-} & 11000 \\ \hline \end{array}$$

Can anyone either provide those values or help me find them somewhere? Even the reaction equilibrium constants that I can find are only listed at a single temperature (and never this high, because these temperatures are… uncommon).

• Jul 22 '20 at 1:21
• I would suggest that you post this in physics. Astrophysicists would be interested in this type of data. I do vaguely recall Saha equation in atomic spectroscopy related to ionization equilibrium in at very high temperatures. You will not find this data in ordinary chemistry or web. Not everything is out there on the web. Jul 22 '20 at 3:20
• @M.Farooq I will take a look in the Physics Stack Exchange -- thanks for the tip. I'll leave it here too, though, in case someone has more information (even on just to calculate it at a nonstandard temperature). I will look into the Saha Equation, I appreciate the suggestion. Glad that I wasn't just ignorant at not being able to find it! Jul 22 '20 at 15:01
• And thank you, @andselisk, for reformatting. I couldn't figure out how to use LaTeX commands after ten minutes of trying, so I just gave up. Jul 22 '20 at 15:02
• @andselisk Gotcha, I understand now I think. Thank you so much for the tip! Jul 22 '20 at 16:01