# Why is air in atmospheric pressure and room temperature a gas?

This seems like a simple thermodynamics question but I would like clarification. So the absolute critical temperature is 132.5 K (-221.17 F) and the absolute critical pressure is 3.77Mpa (546.7 psi). I understand that for temperatures above the critical point, a pure substance undergoes an illusionary single phase process. The critical point is denoted as the change from a saturated liquid to a saturated vapor state at a single state under a high temperature and high pressure for a particular fluid. I understand this change is indiscernible since it a happens at a single state. Upon learning this, I brainstormed on whether air on normal conditions is treated as an ideal gas since the atm pressure is significantly lower than the critical pressure and the room temperature is significantly higher than the critical temperature. My confusions stems if this is the right intuition or not. Am I proceeding with the correct though process?

Chestermiller
Mentor
Are you asking why it is a gas or why it can be approximated at room conditions as an ideal gas?

Are you asking why it is a gas or why it can be approximated at room conditions as an ideal gas?

I am asking why it can be approximated this way. I did some research and I am wondering if the compressibility factor plays a role if you normalized the properties?

Chestermiller
Mentor
I am asking why it can be approximated this way. I did some research and I am wondering if the compressibility factor plays a role if you normalized the properties?
Sure. From a correspond states plot of the z compressibility factor, the compressibility factor for air at room conditions is very close to 1.0