Gases

1
Gases

• Kinetic-Molecular Theory of Gases
• Notes5

2

• All particles are in constant motion.
• As temperature increases kinetic energy ?

increases
increases

• As gas particles move apart the volume ?

3
Point Masses

• Gas particles are treated as a point with no
  volume and no mutual attraction
• -this is because theyre so small compared to
  the distances between them.

4
Ideal Gases

• A theoretical gas with no volume and no
  attraction.
• A series of theories will be studied about ideal
  gases
• -standard pressure of 101.32 kPa
• -standard temperature of 0C or 273K
• -standard conditions are abbreviated

• STP

5
Therefore

• Kinetic theory explains properties of gases based
  on a molecular view.
• The assumptions are
• The molecules are in continuous, random motion.
• A molecule has negligible volume.
• The forces between molecules are negligible.
• The average kinetic energy depends on the
  temperature.

6
Four Gas Law Variables Are

• V volume
• P pressure
• T temperature
• n number of particles
• (Case is important)

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Behavior of Gases

• Compression
• Expansion
• Diffusion movement of material from high to low
  concentration
• - lighter particles diffuse faster than heavier
  particles
• Effusion- gas escapes through a tiny opening

8
Gas Pressure

• Pressure force/area
• Snowshoes in the snow force is spread out over
  a larger area
• Gas particles exert pressure as they collide with
  the walls of their container
• More particles in a given space, greater pressure
• Barometer is tool used to measure atmospheric
  pressure mercury rises or falls

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Units of pressure

• SI unit is Pascal (Pa)
• 1Pa 1 N/m2 derived from force
• 1atm 760mm Hg 760 torr 101.3 kPa 14.7 psi
• 1torr 1 mm Hg

10
Daltons Law of Partial Pressure

• Total pressure of a mixture of gases is equal to
  the sum of all the pressures of the individual
  gases
• Pg. 392 practice problems

11
Boyles Law

• Relates volume and pressure
• -gas exerts pressure on its containers walls
• -pressure depends on
• number of molecules
• average kinetic energy of the molecules

.

• Pressure P

.
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Boyles Law

• Relates volume and pressure
• -gas exerts pressure on its containers walls
• -pressure depends on
• number of molecules
• average kinetic energy of the molecules

• Plunger applies pressure (now 2P).
• -As pressure doubles, volume
  becomes ½.
• -(note the same number of particles now
  occupying ½ the space)

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Boyles Law

• Boyles Law PVk
• Ppressure
• V volume
• kconstant

• Experiments happen at room temperature(about
  25ºC.) We need to convert the results to STP.

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Boyles Law

• Since and

• then (substituting for k)

15
Boyles Law

• Since and
• then (substituting for k)

• or

16
Boyles Law

• Since and
• then (substituting for k)
• or

• Units
• pressure - kPa
• volume - cm3

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Problem a gas is collected in a 242 cm3
container at 87.6 kPa. What is its volume at
STP?

• V1 P1 V2 P2

101.325 kPa

• Think pressure goes from 87.6 kPa to 101.325
  kPa so Volume should be________ than 242 cm3
• Math

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• so

• Note 209 lt 242cm3
• Now do CMC 358 1, 2, 3(a,c,e) and 4(a,c,e).