Supercritical Helium: Does PV=nRT Apply?

[xnk]

How closely, if at all, does helium in the supercritical phase obey PV=nRT?

 

[gravenewworld]

I think you have to use the VanDer Waal Equation for real gasses here which is

(P+(n^2a/V))(V-nb)=nRT

Here the terms a and b are dependent on the critical pressure and temperatures of the gas in question.

a=27R^2Tc^2/64Pc and b=RTc/8Pc

where Tc is the critical temperature and Pc is the critical pressure.

To determine how ideal helium will be have you can also find the compressibility factor z. For an ideal gas z always equals 1.

for a real gas

z=PV/nRT=(V/V-nb)-(an/RTV)

From that you can see how much helium will deviate from an indeal gas behavior.

 

[ravenprp]

Supercritical helium is a unique state of matter that occurs when helium is subjected to both high pressure and high temperature. In this state, the helium exists as a single phase, with properties that are in between those of a gas and a liquid. This raises the question of whether the ideal gas law, PV=nRT, still applies to supercritical helium.

The ideal gas law, PV=nRT, is a fundamental equation in thermodynamics that describes the relationship between the pressure, volume, temperature, and number of moles of an ideal gas. It is based on the assumptions that the gas molecules have no volume and do not interact with each other. However, in the supercritical phase, these assumptions do not hold true.

Firstly, in the supercritical phase, the helium molecules do have a finite volume due to the high pressure. This means that the volume of the gas cannot be neglected and must be accounted for in the ideal gas law. Secondly, at high pressures and temperatures, the helium molecules begin to interact with each other, deviating from the behavior of an ideal gas. This results in a decrease in the compressibility of the gas, meaning that the volume does not decrease as much as expected with an increase in pressure.

Therefore, while the ideal gas law can still be used as an approximation for supercritical helium, it does not fully describe its behavior. In order to accurately predict the properties of supercritical helium, more complex equations of state must be used, such as the van der Waals equation or the Peng-Robinson equation.

In conclusion, while the ideal gas law can provide a rough estimate of the behavior of supercritical helium, it does not fully apply in this state. The unique properties of supercritical helium require more complex equations to accurately describe its behavior.