The Gas Laws

1
The Gas Laws
2
What is a gas?

• As a substance changes from solid to liquid to
  gas, it has more entropy (randomness). It will
  also have more kinetic energy.
• Can you think of an exception? (hint water)

3
Kinetic Theory of Gases

• The kinetic theory of gases says that moving gas
  molecules collide with the container they are in.
  These collisions cause gas pressure.
• What would cause more collisions?

4
Kinetic Theory of Gases
Basis all matter is composed of tiny particles
called molecules that are in constant motion.
Gas molecules are small compared with the
average distances between them collide without
loss of kinetic energy exert almost no forces on
one another outside of collisions
Thus, a gas is mostly an empty space
The absolute temperature of a gas is proportional
to the average kinetic energy of its molecules .
Explain.
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Boyles Law

• Boyles law relates gaseous volume and pressure
  under constant temperature
• P1 V2
• --- ----
• P2 V1

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Boyles Law
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Examples of Boyles Law
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Charles Law

• Charles Law relates V (volume) and T
  (temperature).
• As pressure increases, temperature _____?
• Both Charles and Boyles Laws assume something is
  constant. What is it?

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Charles Law

• Each of these balloons is at a different
  temperature.
• Find the one placed in the freezer, the one
  outdoors in the sun and the one in the classroom.

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Examples of Charles Law
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Combined Gas Law
Combined Boyles and Charles laws give the ideal
gas law
p1 V1 p2 V2 ------- ------- T1
T2
At constant T (T1 T2) we have Boyles law At
constant p (p1 p2) we have Charles law
p V ----- const T
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Explain This!
Watch it! http//www.youtube.com/watch?vo9v9Dn4il
do
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What about this?
Watch it! http//www.youtube.com/watch?vvcsxB5dKJ
Mg
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Bet you cant explain this! (take a deep breath
first)
Watch it! http//www.youtube.com/watch?vJFUu-pn7Q
tg
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Finally, try this one
Watch it! http//www.youtube.com/watch?vsNOXFiJ4I
DU
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Ideal Gas Law

• An ideal gas has particles that do not have any
  mass or size. The collisions of particles with
  one another are elastic (no energy is lost)
• Real gases are not ideal, but ideal gas laws do
  approximate true conditions except at very high
  pressure and temperature.

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Ideal Gas Law

• PV nRT
• P pressure
• V volume
• n number of moles
• R gas constant
• (8.31 L Kpa K-1mol-1 or
• -- 8.205 X 10-2 L atm K-1mol-1--
• T temperature in Kelvin (why Kelvin??)
• (Kelvin 273 Celsius
• Gas Law Song

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What is the volume of 1 mole of gas?

• Volume is related between all gases by Avogadro's
  hypothesis, which states Equal volumes of gases
  at the same temperature and pressure contain
  equal numbers of molecules
• Sing along with Michael Offutt!

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So, a mole of gas has a volume of 22.4 L. Any
gas will doas long at it is at STP
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What is STP?

• Standard Temperature and Pressure
• IUPAC
• temperature of 273.15 K (0 C)
• absolute pressure of 1 atm,
• --------------------------------------------------
  --
• An unofficial, but commonly used standard
  (SA(ambient)TP)
• temperature of 298.15 K (25 C, 77 F)
• absolute pressure 1 atm).