The Gas Laws

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The Gas Laws
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Gases have properties which we can observe with
our senses

• These properties include pressure (p),
  temperature, mass, and the volume (V) which
  contains the gas.

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Gas in a Balloon

• Gas molecules inside a volume (a balloon) are
  constantly moving around freely.
• During this molecular motion they frequently
  collide with each other and with the surface of
  any enclosure there may be (in a small balloon
  there are many billions of collisions each
  second).

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Factors that Affect Gas Pressure

• What changes might affect the pressure of a gas
  in a container?
• Temperature
• Volume
• Number of particles

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Section 2 Behavior of Gases
Chapter 3
Describing Gas Behavior

• Temperature Temperature is a measure of how
  fast the particles in an object are moving.The
  faster the particles are moving, the more energy
  they have.
• Volume Volume is the amount of space that an
  object takes up. Because gas particles spread
  out, the volume of any gas depends on the
  container that the gas is in.

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Section 2 Behavior of Gases
Chapter 3
Describing Gas Behavior, continued

• Pressure The amount of force exerted on a given
  area of surface is called pressure. You can think
  of pressure as the number of times the particles
  of a gas hit the inside of their container.

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Robert Boyle investigated the relationship
between the volume of a gas and its pressure
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Volume and Pressure Relationship

• Reducing the volume of a gas increases its
  pressure if the temperature of the gas and the
  number of particles are constant

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Volume vs Pressure

• When he changed the pressure the volume responded
  in the opposite direction.

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Boyles Law

• Boyles Law states that the volume of a gas is
  inversely proportional to its pressure if the
  temperature and the number of particles are
  constant.

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A practical application of Boyles Law is the
action of a syringe.

• When fluids are drawn into a syringe, the volume
  inside the syringe is increased.
• the pressure decreases on the inside
• the pressure on the outside of the syringe is
  greater
• Fluids are forced into the syringe.

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• pushing the plunger in decreases the volume on
  the inside
• increases the pressure inside and makes it
  greater than outside
• fluids are forced out.

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• The bubbles exhaled by a scuba diver grow as the
  approach the surface of the ocean.
• Deep sea fish die when brought to the surface.
• Pushing in the plunger of a plugged-up syringe
  decreases the volume of air trapped under the
  plunger.

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Charles Law

• Doubling the temperature of a gas doubles its
  volume, as long as the pressure of the gas and
  the amount of gas isn't changed.

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Temperature Pressure Relationship

• The pressure of a gas increases if the
  temperature increases.

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Why does gas pressure increase when the
temperature increases?

• The particles in a gas are moving. They bump
  into the walls creating a pressure.
• When a gas is heated, its particles speed up.

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There are two ways that this increases the
pressure

• the faster particles bump into the container
  walls more often
• each collision is harder because the particles
  are moving faster.

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• A football inflated inside and then taken
  outdoors on a winter day shrinks slightly.
• A slightly underinflated rubber life raft left in
  bright sunlight swells up
• The plunger on a turkey syringe thermometer pops
  out when the turkey is done

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Gas Behavior Laws

• Boyles Law Boyles law states that for a fixed
  amount of gas at a constant temperature, the
  volume of the gas is inversely related to
  pressure.
• P1V1 P2V2
• Charless Law Charless law states that for a
  fixed amount of gas at a constant pressure, the
  volume of the gas changes in the same way that
  the temperature of the gas changes.
• T1V2 T2V1

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Section 2 Behavior of Gases
Chapter 3
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• http//www.chem.iastate.edu/group/Greenbowe/sectio
  ns/projectfolder/flashfiles/gaslaw/boyles_law_grap
  h.html
• http//www.jersey.uoregon.edu/vlab/Piston
• http//www.grc.nasa.gov/WW/K-12/airplane/Animation
  /frglab2.html

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The Combined Gas Law

• Combination of Boyles and Charles laws
• The volume of gas is directly proportional to the
  temperature and inversely proportional to the
  pressure.
• P1V1 P2V2
• T1 T2

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  How You Breathe

• Your lungs are are made of spongy, elastic tissue
  that stretches and constricts as you breathe.
• The airways that bring air into the lungs are
  made of smooth muscle and cartilage, allowing the
  airways to constrict and expand.

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• What we need is a way to create air pressure to
  draw the air into our bodies.
• Atmospheric pressure is about 760 mm Hg. 
• Since the flow is always from an higher to lower,
  we have to be able to make our respiratory tract
  have a lower pressure than 760 mm Hg.

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• How can we decrease the pressure within our
  respiratory tract?

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This is the trick.

•   In order to decrease the pressure within our
  respiratory tract, we have to expand our
  container, our chest. If we can expand our chest,
  the air pressure within will fall, and air will
  rush into our respiratory tract.

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Inhaling

• When you inhale, the diaphragm and the muscles
  between your ribs contract and expand the chest
  cavity.

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• This expansion lowers the pressure in the chest
  cavity below the outside air pressure. Air then
  flows in through the airways (from high pressure
  to low pressure) and inflates the lungs.

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Inhalation and exhalation
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• When you exhale, the diaphragm and rib muscles
  relax and the chest cavity gets smaller.
• The decrease in volume of the cavity increases
  the pressure in the chest cavity above the
  outside air pressure.
• Air from the lungs (high pressure) then flows out
  of the airways to the outside air (low pressure).
  The cycle then repeats with each breath.

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• http//www.smm.org/heart/lungs/breathing.htm