Chapters 10 and 12: Gases

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Chapters 10 and 12 Gases

• A. Kinetic Theory (Ch. 10)
• Kinetic energy (K.E.) the energy due to motion
• Kinetic theory particles in all states of
  matter are in constant motion
• - gas particles are spread out, move
  in straight paths, and fill up the shape of
  its container
• - gas particles collide randomly with
  each other and are perfectly elastic
  (energy is completely transferred)

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• B. Gas Pressure (Ch. 10)
• Gas pressure the pressure or force exerted by
  the collisions gas particles
• Atmospheric pressure the pressure that results
  from collisions of air
  molecules with objects
• - the higher the elevation
  (mountain vs. sea level), the lower
  the atmospheric pressure (thinner air)
• Barometer measures atmospheric pressure

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• Units of pressure
• 1 atm (atmosphere)
• 101.3 kPa (kiloPascals)
• 760 mmHg (millimeters of Mercury)
• 760 torr (torr)
• Convert using either proportions or factor-label
  method
• STP (Standard Temperature and Pressure)
• 0 ?C 273 K (temperature)
• 1 atm or its equivalents (pressure)
• Gases are temperature and pressure dependent

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• C. Kinetic energy and Kelvin temperature (Ch.
  10)
• Kelvin temperature an adjusted scale from the
  Celsius temperature used for gases
  (see gas laws)
• - no degree symbol used (K)
• - formula K ?C 273
• - Kelvin temp is directly
  proportional to K.E.
• ex. At 200 K gas particles have 2x the K.E.
  compared to gas particles at 100 K
• Absolute zero the temp when all particles stop
  moving (0 K -273 ?C -459 ?F)

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• Very cold temperatures vs. absolute zero
• ex. Coldest temp. on earth (Antarctica)
• 184 K -89 ?C -128 ?F
• Liquid nitrogen
• 77 K -196 ?C -321 ?F
• Pluto
• 40 K -233 ?C -387 ?F
• Absolute zero
• 0 K -273 ?C -459 ?F

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• D. Liquids ? Gases (Ch. 10)
• Vapor pressure the pressure when a liquid
  starts to evaporate, and the gas
  particles in a sealed container collide
  with the container wall
• - force of the gas above a liquid
  in a sealed container
• - as temperature increases, so
  does the vapor pressure
• - after time, the vapor (gas)
  starts to condense (liquid) until it
  reaches equilibrium (the rate of
  vaporization equals the rate of
  condensation)

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• Vapor pressure
• ex.

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• Boiling point (B.P.) the temperature at which
  the vapor pressure is equal to the
  external pressure (atmospheric pressure)
• Normal boiling point the B.P. at 1 atm (or its
  equivalents) of pressure
• ex.

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• Graph of vapor pressure vs. temperature
• ex.

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• E. Solids ? Gases (Ch. 10)
• Sublimation when a solid goes straight into
  vapor (gas) without becoming a liquid
• - these solids have very high vapor
  pressures (volatile)
• ex. dry ice (CO2(s) ? CO2(g))
• ice cubes after time in the freezer
• freeze-dried foods
• air fresheners
• naphthalene (moth balls)

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• F. Adding/Removing Gas (Ch. 12)
• Review
• Gases have a lot of K.E.
• Gases fill their container
• Empty/open space between gas particles
• Gases are compressible (squeezed together)
• Variables that affect gases
• P (pressure)
• V (volume)
• T (temperature, in Kelvin)
• n (moles)

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• Adding gas to a sealed container
• Increases the number of collisions
• More collisions, greater pressure
• Too much pressure, container breaks
• If you add 2x the gas, the pressure doubles
• Removing gas from a sealed container
• Pressure decreases
• Gas goes from a high-pressure sealed container to
  a low-pressure surroundings
• Gases prefer to be at low pressure so there is
  more room for the particles to move around and
  collide with one another

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• G. Boyles Law (Ch. 12)
• Boyles law pressure vs. volume at a constant
  temperature (same temperature)
  with no gas being added/removed
• - formula P1 x V1 P2 x V2
• - both Ps and Vs need to be in the
  same units
• - inverse relationship (P ?, V ?)
• ex.

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• ex. A balloon contains 30.0 L of He(g) at 101.3
  kPa. What is the volume when the balloon has a
  new pressure of 0.5 atm?
• P1 x V1 P2 x V2
• (1 atm) x (30.0 L) (0.5 atm) x V2
• 0.5 atm 0.5 atm
• V2 60 L

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• H. Charless Law (Ch. 12)
• Charless law temperature vs. volume at a
  constant pressure (same pressure) with no
  gas being added/removed
• - formula V1 V2
• T1 T2
• - both Ts must be in Kelvin
• - both Vs must be the same unit
• - direct relationship (T ?, V ?)
• ex.

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• Why Kelvin temperature?

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• ex. A balloon at 24 ?C has a volume of 4 L. The
  balloon is heated to 58 ?C. What is the new
  volume of the balloon?
• V1 V2
• T1 T2
• (4 L) x (331 K) (297 K) x V2
• 297 K 297 K
• V2 4.46 L

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• I. Gay-Lussacs Law (Ch. 12)
• Gay-Lussacs law temperature vs. pressure at a
  constant volume (same volume)
  with no gas being added/removed
• - formula P1 P2
• T1 T2
• - both Ts must be in Kelvin
• - both Ps must be the same unit
• - direct relationship (T ?, P ?)
• ex.

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• J. Combined Gas Law (Ch. 12)
• Combined gas law combines all 3 main gas laws
• - formula P1 x V1 P2 x V2
• T1 T2
• - cross out the variable (if any)
  that remains constant or not
  mentioned in the problem
• - both Ts must be in Kelvin
• - both Ps and Vs must have the
  same units
• - STP 0 ?C (273 K) and 1 atm

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• ex. A filled balloon has a volume of 30 L at 40
  ?C and 153 kPa. What will the volume of the
  balloon be at STP?
• P1 153 kPa P2 101.3 kPa
• V1 30 L V2 ?
• T1 313 K T2 273 K
• V2 (V1 x P1 x T2) / (P2 x T1)
• V2 (30 L x 153 kPa x 273 K) / (101.3 kPa x
  313 K)
• V2 39.5 L

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• K. Ideal Gas Law (Ch. 12)
• Ideal gases the way all gases should behave in
  a perfect world
• Real gases the way gases behave in the real
  world
• Ideal gas law describes the behavior of ideal
  gas
• formula P V n R T
• P (atm)
• V (L) at STP 22.4 L
• n (moles)
• T (K)
• Gas law constant (R) 0.0821 (L?atm)/(moles?K)
• (will be given on test/quiz)

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• ex. A 20.0 L container is filled with gas to
  obtain a pressure of 202.6 kPa at 28 ?C. How
  many moles of N2(g) are in the container?
• P V n R T
• n (P V) / (R T)
• n (2 atm) x (20.0 L)
• (0.0821 L?atm/moles?K) x (301 K)
• n 1.62 moles

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• L. Daltons Law of Partial Pressures (Ch. 12)
• Daltons law the sum of the partial pressures
  of each gas in a mixture is equal to
  the total pressure at a constant
  temperature at volume
• - formula PT P1 P2 P3
• ex. What is the partial pressure of O2 at STP if
  the other partial pressures of air are
• N2 79.10 kPa CO2 0.04 kPa Ar 0.94
  kPa
• 101.3 kPa 79.1 kPa 0.04 kPa 0.94 kPa
  PO2
• 101.3 kPa 80.08 kPa PO2
• PO2 21.22 kPa