Chapter 12 – Gas Laws

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Chapter 12 – Gas Laws Powered By Docstoc
					Chapter 13 –

  Gas Laws
Properties of Gases
  Kinetic Molecular Theory
• Explains behavior of gases at
  molecular level
• Developed in the Mid-1800’s
• Assumes an ideal gas
  – NO interactions between gas particles
  – Especially in collisions.
                 Collisions
• Assume collisions are elastic in ideal gas

  – Elastic – no energy transferred
  – Inelastic – energy transferred from one
    particle to the other, usually in the form of
    heat


• no net attractive or repulsive forces in gas
  particles collisions
            Real Gases
• Must consider transfer of energy in
  collisions due to attractions and
  repulsions of molecules.
• Must consider the volume of gases
         Gases are Fluids
• WHAT!?!?!
• Yes; a fluid is “a substance that
  flows”.
  – Liquid examples include syrup, Hg, Br2
• Gases flow like liquids
  – Dry Ice
• Imagine opening your refrigerator
  door. What happens?
                  Density
• Solids have the highest densities
  – atoms are tightly packed together.
• Liquids have high densities
  – free to move past one another
  – still very close to each other.
• Gases have very low densities.
  – Atoms are far apart
  – Gas volumes are mostly empty space
  – Ignore volume of gas particles and use volume
    of container as volume of gas.
   Gases are compressible
• Gases can be compressed up to 100x
  the original volume.
• For example, 30 mL of air can
  compress to 0.30 mL.
• Why can’t I do it in the syringe?
    Average Temperature
• Temperature is AVERAGE kinetic
  energy where KE=1/2 mv2
• Molecules may possess any value of
  kinetic energy, from zero to infinity
Average Kinetic Energy
              Pressure
• P = Force/Area = N/m2 = Pascal (Pa)

• Gas pressure is exerted on all walls
  and in all directions of a container.

• Pressure is what keeps walls up and
  is responsible for aerosol cans.
  – Examples include pump sprays, oil
    pumps, and vacuum cleaners
     Atmospheric Pressure
• The pressure exerted by the particles in the
  atmosphere that surrounds Earth is called
  atmospheric pressure, or air pressure.
• Air pressure varies at different locations on
  Earth.
    Atmospheric Pressure
• The atmosphere always exerts a
  pressure on Earth.
• Due to the mass of air above us and
  the gravitational pull of the earth.
• Standard atmospheric pressure at
  sea level is 14.7 psi (pounds per
  square inch) or 1 atmosphere (atm)
             Air Pressure
• Air pressure is
  measured using a
  barometer.

• A barometer consists
  of a thin tube closed
  on one end and filled
  with mercury.
             Gas Pressure

• The tube is placed
  so that the level of
  the mercury is
  determined by air
  pressure.
• The mercury rises
  when the air
  pressure increases
  and falls when the
  air pressure
  decreases.
Gas Pressure – Mercury
      barometer
 THERE IS NO SUCH THING
     AS SUCTION!!!
• Gases move from areas of high pressure to areas
  of low pressure.
• That is why we have wind outside.
• Dyson’s vacuum cleaner claim to “Never Lose
  Suction!”
• Vacuum cleaner works
  – A motor removes air from inside the sweeper
  – This creates a vacuum (hence “vacuum” cleaner).
  – Air particles move to low pressure area to even things
    out.
  – As the air travels into the sweeper, it picks up particles
    from the carpet and carries them with it.
• JUST THE SAME WAY THAT WIND CARRIES DIRT
  AND OTHER THINGS WITH IT!!!
      Pressure conversions
• 1.0 atm = 14.7 psi (pounds per square inch)
• 1.0 atm = 101,325 Pascals (Pa)
• 1.0 atm = 101.325 KiloPascals (kPa)
• 1.0 atm = 760 mmHg
• 1 mmHg = 1 torr

• YOU must know these conversions,
  they will NOT be given to you!
            Boyle’s Law
• Relates Volume and Pressure
• You will investigate this relationship
  tomorrow.
• P1V1 = P2V2
           Thank you!!!
• Your attention today is greatly
  appreciated!

				
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