Cp/ Cv Ratios

D'oh..... I need reminding of what Cp and Cv are!!

Cp/Cv is the ratio of fluid's specific heat at a constant pressure to its specific heat at a constant volume.... Hope this reminds!!!

First and foremost, air is a composite of gases, so it can not be used as a standard in this case, given that the Cp and Cv are dependent on the molecular composition and structure.

I would therefore opine that there is and should exist no corrollation of the form you are seeking information on.

No. What you suggest is not the case. For example helium has γ = 1.7, with a relative density (w.r.t. air) of 0.14, while argon has γ = 1.7 and a relative density of 1.4.

At the other end of the scale, there is ammonia with Υ = 1.3 and a relative density of 0.59, while carbon dioxide has γ = 1.3 with a relative density of 1.5.

Air is a mixture, but it is primarily a mixture of two diatomic gases (oxygen and nitrogen) and thus has the same γ as if it were a pure gas.

Source for values is Marks' Handbook, 3rd ed.

Cp/Cv is basically dependent on how many molecules are in the gas. Water is 1.3, while the diatomic gases of air are 1.4 and monatomic gases like He and A are higher (I think 1.7).

Beyond triatomic, the ratio doesn't seem to vary drastically from 1.3.