Kinetic Theory of Gasesand Non-Ideal Gases
Kinetic Theory of GasesAn Attempt to Explain Why the Gas Laws Work
Origin of the postulates of the Kinetic Theory of Gases
Origin of postulates part 2
Molecular Motion of Gases
• Far apart
• Free from one another
• Randomly moving
mean free path: average distance traveled between collisions
typically ~ 10-5 cm molecular size ~ 10-8 cm
diffusion: irregular motion of molecules
Velocity of gas molecules and Mean free path
Rotating disk method of measuring velocity distribution
Maxwell-Boltzmann distribution of molecular speeds
same gas (N2) at different temperatures
Maxwell-Boltzmann distribution of molecular speeds different gases at same temperature
Graham’s Law of EffusionEffusion is the leaking of a gas through a small hole.
A Hydrogen fountainillustrating the highdiffusion rate of H2 gas.
Diffusion is related but not identical to effusion.
The collection of a gas over water using a pneumatic trough. This method should not be used for gases that dissolve in water (then use Hg like Priestley).
Dalton’s Law of Partial Pressures
Representative partial pressures (in torr)in inhaled and exhaled air.
In the respiration process, we use O2 and emit CO2as well as humidifying the air that passes through our lungs.
A corollary of Dalton’s Lawis Ptotal = XA P
= mole fraction of gas A times the partial pressure of gas
A
Gay-Lussac’s Law of Combining Volumes
Avogadro’s Hypothesis
Non-Ideal GasesReal gases condense to a liquid.
An ideal gas cannot.
A British term for what we callUHF, Ultra High Frequency
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Modernview
Air Liquefier
Dewar flask (or thermos bottle)
The Compressibility Factor, PV/nRT
Real Gases• Deviation from “Ideal” Gas Law
PV = nRT for an ideal gas at STP, 1 mole = 22.414 L
Experimental Data 1.0000 mole of gas
Gas Volume (L) Deviation from Ideality
H2 22.433 +0.085 %He 22.434 +0.089 %
N2 22.404 - 0.045 %
O2 22.397 - 0.076 %
CO2 22.260 - 0.687 %
NH3 22.079 - 1.495 %
Properties of Real Gases
Properties of Real Gases
Decrease due toIntermolecularAttractive Forces
Increase due toMolecular Volumesignificant
The destructive effectof higher temperatures
Van der Waals’ equationwhich corrects for the non-ideal properties of gases
Correcting for Deviations from Ideal Gases
• for ideal gas: PV = nRT (Ideal gas law)
• for “real” gas:
(Preal + a n2 )(Vreal – nb) = n RT
V2
attractive forcecorrection
molecularvolume
correction
Van der Waals’Equation
The a and b factors in Van der Waals’ equation
Table continued
Two calculations
Solution of the Van der Waals equation to find the Critical Temperature and Critical Pressure
Liquid NitrogenAir that is so cold that it becomes a liquid (probably the coolest stuff you will ever see)
Liquid NitrogenIce Cream