TOPIC: Kinetic-Molecular Theory (KMT)

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TOPIC Kinetic-Molecular Theory (KMT)

• Do Now packet page __
• Relationship between Temp and Average Kinetic
  Energy

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Models

• Scientists use models because simpler than real
  life
• Kinetic-molecular theory can be extended to all
  phases of matter

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Kinetic-Molecular Theory (KMT) as it pertains to
ideal gases

• There are 4 assumptions to the KMT

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Real vs. ideal gas

• Ideal gas obeys assumptions of KMT all the time
• Its a model
• It doesnt exist
• Real gases follow KMT most of time, but not at
  high pressure low temperature
• KMT breaks down when molecules are close together

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• 1) Gases consist of spherical molecules moving
  in constant, random, straight-line motion
• Random, straight-line?
• - move in straight
• lines until hit
• something, then can
• bounce
• off at any angle

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• 2) Gas particles undergo elastic collisions
  with each other and with walls of container
• Elastic means total KE is conserved
• KE does not get converted to heat or sound or any
  other kind of energy
• KE can be transferred between particles

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• 3) Gas molecules separated by such great
  distances that the volume of molecule is
  negligible (not significant)
• Ideal gasses are considered not to have volume,
  but they still have a mass, so scientists call
  this a point mass

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• Gas molecules do not attract or repel each other

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• Real gases do interact with one anotherthats
  why water vapor condenses

Intermolecular forces
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Ideal vs Real

• Real ( at high pressure low temperature)
• Particles take up space (they have volume)
• All gas particles are subject to intermolecular
  interactions

• Ideal
• Particles themselves take up no space
• Particles have no intermolecular forces

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Example N2(g)

• At a low temperature, the kinetic energy is

low, which means their intermolecular forces are
strong enough to hold them together Nitrogen gas
become liquid Nitrogen
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Propane
If you increase the pressure, the volume
decreases, which forces particles closer
together. They will become a liquid
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VIDEO LINK

• http//ed.ted.com/lessons/describing-the-invisible
  -properties-of-gas-brian-bennett