# Why isn't Argon's heat capacity ratio constant with temperature?

The Wikipedia Heat Capacity Ratio page claims that Argon has a different ratio at -180°C, that would make it the only noble gas that doesn't always hold a ratio of ~1.660, why is that ?

• Why should it not be some function of temperature? Just because the others are not listed as having different heat capacities does not mean that they don't. In particular, compare the low temperature listed for Ar with its melting point. – Jon Custer Apr 25 at 14:50

For an ideal monatomic gas (the noble gasses being monatomic, but not strictly ideal), $$\gamma = \frac 5 3 = 1.6666...$$. For a real monatomic gas, these values will vary somewhat with temperature and pressure.