Behavior of Gases

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Behavior of Gases
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Kinetic Molecular Theory (KMT)

• Theory related to motion of particles.
• Particles of an ideal gas
• have elastic collisions.
• are in constant, random, straight-line motion.
• have an avg. KE directly related to Kelvin
  temperature.
• have no volume.
• dont attract or repel each other.

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Real Gases

• But.particles in a REAL gas
• Have their own volume
• Although its really small relative to total
  volume of gas
• Can attract each other
• Weakly, usually Van Der Waals force only!!

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When is a Gas Most Ideal?

• Thus, gas behavior is most IDEAL
• When gas particles are tiny, have weak attractive
  forces, are far apart and moving fast.
• at low pressures
• at high temperatures
• when very small in size
• when nonpolar
• PLIGHT

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Characteristics of Gases

• Gases expand to fill any container uniformly.
• Are in random motion, have no attraction
• Gases have very low densities.
• Particles have no volume lots of empty space

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Characteristics of Gases

• There is a lot of free space in a gas.
• Gases can be compressed.
• no volume lots of empty space

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Gas Pressure
Gas pressure is a gauge of the number and force
of collisions between gas particles and the walls
of container The SI unit for pressure is the
pascal (Pa), but other pressure terms include
atmospheres (atms), millimeters of mercury
(mmHg), and torr. Standard pressure in every
unit for pressure  1 Atm 101.325kPa
101,325 Pa 760 torr 760 mmHg 14.7lb/in2 
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Factors Affecting Gas Pressure

• Number of Moles (Amount of gas)
• As of particles increase, the number of
  collisions with the container wall increases.
• Draw an Example

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Factors Affecting Gas Pressure

• Volume
• Smaller the volume, the greater the pressure
  exerted on the container.
• Draw an Example

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Factors Affecting Gas Pressure

• Temperature
• As temp. increases, KE increases, this increases
  frequency of collisions making pressure increase.
• Draw an Example

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Measuring Gas Pressure

• Barometer
• measures atmospheric pressure
• (developed by Torricelli in 1643)

Note The weight of the column of mercury is
equal to the force of the atmospheric pressure.
It the column was water the column would have to
be 34 feet tall!!
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Atmospheric Pressure
"Atmospheric Pressure" is defined as the force per unit area exerted against a surface by the weight of the air above that surface. The pressure at point "X" increases as the weight of the air above it increases. The same can be said about decreasing pressure. In the mountains there is less air above you so less pressure. Since gases are compressible, this creates an environment in the mountains that has less air per unit volume. It will be harder to breathe in the mountains because there is actually less O2 per volume compared to at sea level.
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• Hg rises in tube until force of
• Hg (down) balances the force
• of atmosphere (pushing up).
• (Just like a straw in soft drink)
• Worlds Longest Vertical Straw
  https//youtu.be/HUmZrtiXDik
• Column height measures
• pressure of atmosphere
• 1 standard atmosphere (atm) 760 mm Hg (or
  torr)

So how dense is Mercury? Watch and find
out. https//www.youtube.com/watch?featureplayer_
embeddedvRm5D47nG9k4
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• Standard Pressure (Sea Level)
• 101.3 kPa (kilopascal)
• 1 atm
• 760 mm Hg (also called torr)
• You may be asked to convert between units of
  pressure!

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Measuring Gas Pressure

• Manometer
• measures contained gas pressure

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http//www.kentchemistry.com/links/GasLaws/manBar.
htm
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Working withFormulas

• The Gas Laws

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• Gas properties can be modeled using math.
• Model depends on
• V volume of the gas (L)
• T temperature (K)
• n amount (moles)
• P pressure (atmospheres or kPa)

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STP
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Temperature

• Always use absolute temperature (Kelvin) when
  working with gases.

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Boyles Law

• Pressure and volume of a gas are inversely
  related
• at constant mass temp

Robert Boyle (1627-1691). Son of Earl of Cork,
Ireland.
PV k
Cartesian Diver https//www.youtube.com/watch?fea
tureplayer_embeddedv3yvSQuTP4T4
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Boyles Law

• Since P x V is always a constant
• P1 x V1 P2 x V2

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• Ex
• Consider a 3.0 L sample of gaseous SO2 at a
  pressure of 1.0 atm. If the pressure is changed
  to 1.5 atm at a constant temperature, what will
  be the new volume of the gas?

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Piston Model Note Inverse relationship. As
volume decreases, pressure increases.
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Boyles LawMass and Temp are Constant
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Boyles Law
Balloon https//youtu.be/bW0j936U4EU Pierre and
Marie Peeps in a vacuum https//www.youtube.com/w
atch?vlfNJJEdKgLU Cartesian Diver
https//www.youtube.com/watch?vsNOXFiJ4IDU
Balloon in a Vacuum
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Charles Law

• Volume and absolute temp. (K) of a gas are
  directly related
• at constant mass pressure

Jacques Charles (1746-1823). Isolated boron and
studied gases. Balloonist.
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• Think of it this way.
• As temperature of the gas increases, gas
  molecules begin to move around more quickly and
  hit the walls of container with more force, thus
  the volume will increase.
• Keep in mind that you must use only
  the Kelvin temperature scale when working with
  temperature in all gas law formulas!

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Charles Law

• Since V/T is always a constant
• V1 V2
• T1 T2

https//www.youtube.com/watch?featureplayer_embed
dedvXHiYKfAmTMc Can Crush https//www.youtube.co
m/watch?vvcsxB5dKJMg
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• Ex
• A sample of gas at 15ºC and 1 atm has a volume of
  2.50 L. What volume will this gas occupy at 30ºC
  and 1 atm?

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Charles Law Mass and Pressure are Constant
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Charles Law
Pour Liquid Nitrogen on Balloon!!
Bill Bye Vaccuum https//www.youtube.com/watch?v
lfNJJEdKgLU Can Crush https//www.youtube.com/wat
ch?vc5_ho2sc0fc Big Can Crush https//www.youtube
.com/watch?featureplayer_embeddedvUy-SN5j1ogk h
ttp//group.chem.iastate.edu/Greenbowe/sections/pr
ojectfolder/flashfiles/gaslaw/charles_law.html htt
p//www.pinnaclescience.com/demo.htm
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Gay-Lussacs Law

• Pressure and absolute temp. (K) of a gas are
  directly related
• at constant mass volume

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Gay Lussacs Law

• Since P/T is always a constant
• P1 P2
• T1 T2

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• Ex
• Find the final pressure of gas at 150. K, if the
  pressure of gas is 210. kPa at 120. K if the
  volume remains constant

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Review of 3 Gas Laws
Summary of Changing Variables http//www.mhhe.com/
physsci/chemistry/essentialchemistry/flash/gasesv6
.swf
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Combined Gas Law (on Ref Table)
The good news is that you dont have to remember
all three gas laws! We can combine them into a
single equation. If you should only need one of
the other gas laws, you can cover up the item
that is constant and you will get that gas law!
P1V1T2 P2V2T1
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https//www.youtube.com/watch?featureplayer_embed
dedvt-Iz414g-ro
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Example

• A sample of He (g) has a volume of 0.180 L, a
  pressure of 0.800 atm and a temperature of 29C.
  What is the new temperature (C) of the gas at a
  volume of .090 L and a pressure of 3.20 atm?

• Set up Data Table
• P1 0.800 atm V1 .180 L T1 302 K
• P2 3.20 atm V2 .090 L T2
  ??