Warm-Up

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Warm-Up
Label your new warm-up/cool-down log The
Properties of Gases
At 20oC, molecules in the air move over 1000 mph.
At this speed, the smell of pizza made in LA
should reach our school in about 30 minutes.
Why dont we smell all of these fast moving
molecules?
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Chapter 13.1 The Nature of Gases
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Chapter 13.1 The Nature of Gases
After this section 13.1, we will move
onto Chapter 14, The Behavior of Gases
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Todays Learning Objectives
--What KMT theory is and its five main
assumptions --Know difference between ideal and
real gases --Know how scientists define
pressure --Be able to convert between various
pressure units --How a barometer works --What STP
is
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Kinetic Molecular Theory (KMT) of Gases

• KMT is a model to explain the behavior of gaseous
  particles
• A gas is ideal (ideal gas) if we make the
  following 5 assumptions of KMT

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KMT Assumptions

• Particles are in constant, random, straight line
  motion. They possess energy in motion, kinetic
  energy.
• The actual volume of gas particles is negligible.
  Particles are far apart.

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KMT Assumptions

• Particles are in constant, random, straight line
  motion. They possess energy in motion, kinetic
  energy.
• The actual volume of gas particles is negligible.
  Particles are far apart.

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KMT Assumptions

• 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.

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KMT Assumptions

• 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.

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KMT Assumptions

• Collisions between gas particles and between
  particles and container are elastic collisions
• An elastic collision means no loss of kinetic
  energy (KE)

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KMT Assumptions

• Collisions between gas particles and between
  particles and container are elastic collisions
• An elastic collision means no loss of kinetic
  energy (KE)

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Real Gas vs Ideal Gas

• KMT breaks down at low temperatures and very high
  pressures
• KMT breaks down the more polar the gas is ----
  Helium gas is more ideal than water vapor

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Pressure

• Pressure is defined as the force per unit area on
  a surface ..
• Pressure force/area (N/cm2 or N/m2)
• Earths atmosphere pushes down on us with
  pressure of 10.1 N/cm2 (1.03 Kg per cm2)

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Measuring Pressure - Barometer
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Units of Pressure

• 1 mm Hg millimeters of Mercury
• 1 torr 1 mm Hg
• 1 atm 760 mm Hg 760 torr
• (average atmospheric pressure at 0oC at sea
  level)
• SI Unit is the Pascal (Pa) Pressure of one
  Newton acting on 1 m2
• 1 atm 101.325 kPa 101,325 Pa

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Standard Temperature and Pressure

• 1 atm
• 0oC
• Called STP

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Homework
-Read Chapter 13.1 -Page 407 26-34
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Cool Down?
If you read a pressure gauge at 670 kPa, how many
atmospheres of pressure is there?