Behavior of Gases

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Behavior of Gases

• Ch 12 Prentice Hall

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Kinetic Theory

• ? Gases are composed of SMALL, SEPARATE particles
  called MOLECULES.
• ? Gas molecules are in CONSTANT MOTION
• ? All COLLISIONS between particles are PERFECTLY
  ELEASTIC
• ? The MOLECULES of a gas display no ATTRACTION or
  REPULSION for one another.

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Kinetic Theory

• ? The AVERAGE KINETIC ENERGY of the molecules is
  DIRECTLY PROPORTIONAL to the KELVIN temperature
  of the gas.

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Ideal Gas

• ? Gas whose BEHAVIOR conforms to the KINETIC
  THEORY -it is THEORETICAL.

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• Gas Pressure
• Pressure FORCE AREA ____ atm
• Atmospheric Pressure - the PRESSURE the earths
  ATMOSPHERE exerts due to its WEIGHT.
• Barometer
• ? Instrument used to measure ATMOSPHERIC
  PRESSURE
• ? Invented by TORRICALLI

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The Combined Gas LawCombines the following laws
and equations together
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Charles law
Variation of gas volume with temperature while
pressure is kept constant
V1/T1 V2/T2
T (K) t (0C) 273.15
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Boyles Law
P1V1 P2V2
Pressure and volume units can be any variant of
pressure and volume HOWEVER the units MUST agree
for both pressures and both volumes!
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Combined Gas Law

• ? Expresses the relationship between the
  PRESSURE, VOLUME and TEMPERATURE of a FIXED
  amount of GAS.
• Equation P1V1 P2V2
• T1 T2

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STANDARD TEMPERATURE AND PRESSURE

• STP CONDITIONS
• 273 K
• 1 atm 760 mmHg

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Combined Gas Law

• Ex A sample of gas has a volume of 201 L when
  its temperature is 293 K and its pressure is 224
  mmHg. What volume will the gas occupy at STP?
• V1 201 L V2 ?
• T1 293 K T2 273 K
• P1 224 mmHg P2 760 mmHg
• (224) (201) (760) x
• (293) (273)
• (224) (201) (273) (293) (760) x
• X 55 L

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Diffusion

• ? The RAPID spreading of a GAS
• Grahams Law of Diffusion
• ? Under the same conditions of TEMPERATURE and
  PRESSURE, gases DIFFUSE at a rate INVERSLEY
  proportional to the SQUARE ROOT of their
  DENSITIES (or MOLAR MASS)
• Equation

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Ideal Gas Equation

• Equation PV nRT
• ? New variables
• n AMOUNT of gas in MOLES
• R UNIVERSAL GAS CONSTANT
• PROPORTIONALLY constant
• value depends on UNITS used for PRESSURE and
  VOLUME
• value of R when using kPa and L
• R 8.314 L . kPa / Mol . K

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• Ex The average lung capacity for a female
  student is 3.9 L. At normal body temperature,
  37oC, and 110 kPa, how many moles of air could
  her lungs hold?
• P 110 kPa V 3.9 L T 310 K (273
  37)
• n X R 8.314 L . kPa / Mol . K
• (110)(3.9) x (310)(8.314)
• (110)(3.9) 0.17 mol
• (310)(8.314)

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Avogadros Law

• ? Equal VOLUMES of different GASES under the SAME
  conditions have the SAME number of PARTICLES.
• ? Conversely, if samples of DIFFERENT GASES at
  the same TEMPERATURE and PRESSURE contain the
  SAME number of PARTICLES, then the VOLUMES of all
  the SAMPLES must be EQUAL.
• ? At STP, one MOLE of any gas occupies a VOLUME
  of 22.4 L.
• ? 22.4 L is the MOLAR VOLUME of a gas.

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Daltons Law of Partial Pressures
Equation PT P1 P2 P3

• ? The PRESSURE of a gas MIXTURE is the SUM of the
  INDIVIDUAL PRESSURES of each gas ALONE.

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• ? Ex Oxygen gas has been collected over water at
  a total pressure of 95.0 kPa and a temperature of
  25oC. What is the pressure of the dry oxygen gas?

PT 95 kPa P vapor 3.17 kPa P oxygen
X 95 3.17 x 91.83 kPa x
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Backdrops - These are full sized backdrops, just
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