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Kinetic Molecular Theory (KMT) of Gases

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... 0.02370 Hydrogen H2 0.2444 0.02661 Nitrogen N2 1.390 0.03913 Oxygen O2 1.360 0.03183 Carbon dioxide CO2 3.592 0.04267 Acetylene C2H2 4.390 0.05136 Chlorine ... – PowerPoint PPT presentation

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Title: Kinetic Molecular Theory (KMT) of Gases


1
Kinetic Molecular Theory (KMT) of Gases
  • KMT is a model to explain the behavior of gaseous
    particles and is based on extensive observations
    of the behavior of gases.
  • If a gas follows all the postulates of the KMT it
    is said to be an ideal gas.

2
Postulates of the KMT
  • Particles are in constant, random, straight line
    motion. Collisions with walls of their container
    generate pressure.
  • The actual volume of gas particles is negligible.
    Particles are far apart. The volume of a gas is
    effectively the volume the particles occupy, not
    their particle volume.

3
Postulates of the KMT
  • Gas particles do not attract or repel.
  • The average kinetic energy of a collection of gas
    particles is directly proportional to the Kelvin
    temperature of the gas.

4
Ideal vs Real Gases
  • How do gas volumes respond under a range of
    conditions (such as changing pressures and
    temperatures)?
  • If a gas is ideal, the graph of PV/RT vs P for
    one mole of gas will have a slope of 1.
  • http//intro.chem.okstate.edu/1314F97/Chapter10/Re
    alGas.html

5
Deviations from Ideality
  • For an ideal gas
  • PV nRT or V nRT/P
  • When you actually measure gas volume at high
    pressures and low temperatures, the Vexperimental
    often does not match Vtheoretical

6
Deviations from Ideality
  • Why doesnt Vexp Vtheor ?
  • If Vexp gt Vtheor
  • ?Some gas particles do repel each other so volume
    is greater than predicted.
  • ?Gas particles do have a volume so volume cannot
    be reduced beyond a certain point.

7
Deviations from Ideality
  • Why doesnt Vexp Vtheor ?
  • If Vexp lt Vtheor
  • ?Some gas particles do attract each other so
    volume is reduced more than expected.

8
Corrections for Deviations from Ideality
  • Johannes van der Waals modified the ideal gas law
    to account for deviations.
  • P x V nRT
  • Pexp a(n/V)2 x (V-nb) nRT
  • ?Pexp a(n/V)2 corrects for attractive or
    repulsive forces (a depends on the particle)
  • ?V-nb corrects for particle volume (b is a
    measure of particle volume)

9
Selected Values for a and b for the van der Waals
Equation
Gas Formula a (L2 atm)/mole2 b L/mole
Helium He 0.03412 0.02370
Hydrogen H2 0.2444 0.02661
Nitrogen N2 1.390 0.03913
Oxygen O2 1.360 0.03183
Carbon dioxide CO2 3.592 0.04267
Acetylene C2H2 4.390 0.05136
Chlorine Cl2 6.493 0.05622
n - Butane C4H10 14.47 0.1226
n - Octane C8H18 37.32 0.2368
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