Calculating Gas Volume with Pressure: Non-Ideal Gas Equation for Mixed Gases

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SUMMARY

The discussion focuses on calculating the volume change of mixed gases, specifically air, under varying pressure using non-ideal gas equations. The Ideal Gas Equation is deemed insufficient for this purpose, prompting suggestions for the van der Waals gas law and the Virial expansion as more suitable alternatives. The importance of considering temperature and pressure ranges is emphasized, particularly near phase change points. Additionally, the need for specific coefficients for air in the van der Waals equation is noted as a potential challenge.

PREREQUISITES
  • Understanding of the Ideal Gas Equation
  • Familiarity with the van der Waals gas law
  • Knowledge of Virial expansion concepts
  • Basic principles of gas behavior under varying pressure and temperature
NEXT STEPS
  • Research the van der Waals gas law coefficients specific to air
  • Study the Virial expansion and its applications in gas calculations
  • Explore the effects of temperature and pressure on gas phase changes
  • Investigate the CRC Handbook for gas properties and equations of state
USEFUL FOR

Researchers, chemists, and engineers involved in gas dynamics, particularly those working with mixed gases and non-ideal gas behavior in various pressure and temperature conditions.

FishBlackpool
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Hi

I am trying to find a formula which can calculate the volume that gas X will decrease by when pressure Y is added to it. Now I have already been pointed to the Ideal Gas Equation, however I read that this is best suited when looking at a single volume of a monatomic gas eg. Argon.

However I wish to experiment (play about) after doing my calculations and instead of messing about with a monatomic gas I would much rather use air so my question is...

Does anyone know a formula I can use to calculate the change in volume of a mixed gas (air) with varying pressure.

PS. I guess a list of pressure volume ratios for air which I could extrapolate from would also be usefull if anyone has them?...but I'd rather do the calculations myself.

Thanks
 
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Well, the next-simplest after the ideal gas law is the van der Waals gas law (which has a pair of parameters). There are some other theoretical models, but I'd suggest a Virial expansion. (I believe that's the mostly used in practice.) It depends really on what temperature/pressure range you're interested in as well.

Note that most equations of state (including the vdw) can get pretty bad results at or near a phase change point.

Hmm, annoyingly the CRC handbook I've got only lists vdW coefficients, and not for air. Shouldn't be hard to find though.

See also:
http://en.wikipedia.org/wiki/Equation_of_state
 

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