SLIDE 1
Real Gases
Real gases deviate from ideal gas law
Quantify deviations using compressibility factor, Z.
Z = PVbar/RT
Z = 1 for ideal gas
Need corrections to account for non- ideal behavior.
CEM 484 Gas Laws 2
Gas Laws: Real Gases Real Gases Real gases deviate from ideal gas - - PowerPoint PPT Presentation
Gas Laws: Real Gases Real Gases Real gases deviate from ideal gas - - PowerPoint PPT Presentation
Gas Laws: Real Gases Real Gases Real gases deviate from ideal gas law Quantify deviations using compressibility factor, Z. Z = PVbar/RT Z = 1 for ideal gas Need corrections to account for non- ideal behavior. Gas
SLIDE 2
SLIDE 3
van der Waals
van der Waals adds two corrections to account for non-ideal behavior
Probability to stick together during collision
Volume of gas atoms
attractive correction
Probability for a molecule to stick after collision a[c]2
volume correction
Account for volume taken up by molecules.
Insert corrections into ideal gas law
CEM 484 Gas Laws 3
SLIDE 4
van der Waals
Compressibility of van der Waals
van der Waals constants are unique to each gas.
CEM 484 Gas Laws 4
a (L2bar2/mol2) b (L/mol) He 0.034 0.024 N2 1.35 0.039 CH4 2.27 0.043
SLIDE 5
Intermolecular forces
Two main forces contribute to non-ideal behavior in neutral molecules.
Dipole-dipole forces: interaction between permanent electric dipole moments.
Dispersion forces: no permanent electric dipole but interaction is through polarized valence electrons
Iclicker: What is the correct ordering for the three gases CH4, N2, and He?
A – aN2 > aCH4 > aHe B – aCH4 > aN2 > aHe
A – aHe > aN2 > aCH4 B – aCH4 > aHe > aN2
CEM 484 Gas Laws 5
SLIDE 6
Gas Density
Performance of gas laws can be monitored using P vs. gas density curves
CEM 484 Gas Laws 6
SLIDE 7
Other gas laws
Two other gas equations
Redlich-Kwong
Pen-Robinson
Tabulated constants
CEM 484 Gas Laws 7
SLIDE 8
Critical Behavior
Critical behavior explored on a P-V diagram.
Critical point – temperature and pressure at which there is no distinction between gas and liquid – a fluid.
Critical point on P-V ̅ isotherms
Critical point defined by inflection point.
CEM 484 Gas Laws 8
SLIDE 9
Iclicker
Assume someone told you that the following was an equation of state for a certain gas. Using the definition of a critical point what is the critical molar volume in terms of the constants B and C?
CEM 484 Gas Laws 9
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