THE BEHAVIOR OF GASES

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THE BEHAVIOR OF GASES

• CHEMISTRY
• CHAPTER 12

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Learn The Gas Laws
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Kinetic Theory Revisited

• Assumptions
• 1. Gases consist of hard, spherical particles
• -Individual volumes of particles are
  insignificant
• -Considerable empty space between particles
  (gases are compressible)

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Kinetic Theory Revisited

• No attractive or repulsive forces exist between
  particles.
• -Gases are free to move around their containers
• -Gases take the size and shape of the container

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Kinetic Theory Revisited

• Gas particles move rapidly in constant random
  motion.
• -Particles travel in straight lines
• -Move independently of each other
• -When there is a collision, it is perfectly
  elastic.
• -No loss in kinetic energy, KE is passed from on
  particle to another
• -KE is directly proportional to the Kelvin
  temperature of the gas

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Variables to Describe a Gas

• Pressure (P) in kilopascals
• Volume (V) in liters
• Temperature (T) in kelvins
• Number of moles (n)
• These will be used in the gas laws learned in
  this chapter of study.

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Factors Affecting Gas Pressure

• Amount of Gas
• -temperature being constant double the number
  of particles and you double the pressure
• -tripling would triple the pressure
• -decreasing the number would cause a decrease in
  pressure (adiabatic change)
• Volume
• -reduce volume by half doubles pressure
• -increasing volume has the opposite effect
• Temperature
• -if average KE doubles, pressure doubles
• -as temperature decreases, particles move more
  slowly and have less KE

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The Gas Laws

• Boyles Law
• Charless Law
• Gay-Lussacs Law
• Combined Gas Law
• Ideal Gas Law

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BOYLES LAW

• For a given mass of gas at a constant
  temperature, the volume of the gas varies
  inversely with pressure.
• Mathematically speaking
• P1V1 P2V2
• Pressure is always constant at a constant
  temperature.

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Charless Law

• The volume of a fixed mass of gas is directly
  proportional to its Kelvin temperature if the
  pressure is kept constant.
• Mathematically speaking
• V1/T1 V2/T2
• Temperature must be in Kelvin.

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Charless Law
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Gay-Lussacs Law

• The pressure of a gas is directly proportional to
  the Kelvin temperature if the volume remains
  constant.
• Mathematically speaking
• P1/T1 P2/T2

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Combined Gas Law

• Cant keep all the laws straight in the ol
  noggin?
• Use the Combined Gas Law
• P1V1/T1 P2V2/T2
• The previous gas laws can be derived from this
  equation.

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Ideal Gas Law

• Along with the prior three variables (pressure,
  temperature, and volume) a fourth needs to be
  considered. The number of moles (n) of a gas in
  a fixed volume at a known temperature and
  pressure.
• Ideal gas Law
• P V n R T
• R Ideal gas constant 8.31 LPa/Kmol

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Ideal Gas Law and Kinetic Theory

• The advantage of using the Ideal Gas Law vs the
  Combined Gas Law is that you will be able to
  calculate the number of moles of a gas present if
  you know the other conditions.
• An important behavior of real gases that differs
  from ideal gases is that a real gas cooled might
  condense to a liquid or solid and thus have a
  volume. Ideal gases would not have a volume at
  this condition.

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Avogadros Hypothesis

• Common sense would tell us that large gas
  molecules, like Cl2, would occupy a larger volume
  than a small one, H2.
• Avogadro proved otherwise!!
• His hypothesis Equal volumes of gases at the
  same temperature and pressure contain equal
  numbers of particles.
• At STP One mole (6.02 x 1023) has a volume of
  22.4 liters.

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Making Sense of Avogadros Constant

• Particles of gas are far apart with a great deal
  of empty space between them.
• Equal numbers of particles of different gases in
  equal volumes at the same temperature should
  exert the same pressure due to the particles
  having the same average kinetic energy and the
  same volume to move about so thus, the same
  number of collisions.

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Daltons Law of Partial Pressures

• At constant volume and temperature, the total
  pressure exerted by a mixture of gases is equal
  to the sum of the partial pressures of the
  component gases.
• The contribution each gas makes to the total is
  the partial pressure of that gas.
• Mathematically speaking
• Ptotal P1 P2 P3 ..

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Grahams Law of Diffusion

• The rate of effusion (diffusion) of a gas is
  inversely proportional to the square root of the
  gass molar mass.
• Diffusion tendency of molecules to move toward
  areas of lower concentration until the
  concentration is uniform.
• Effusion the process in which a gas escapes
  through a tiny hole in its container.

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Grahams Law of Effusion

• Mathematically speaking
• RateA/RateB vmolar massB/vmolar massA
• A helium/air filled balloon is a good example of
  this phenomena. Because helium has a much lower
  mass than nitrogen, it effuses much faster
  through the pores of the balloon.

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• This was a gas!!!!