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The Gas Laws

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Title: The Gas Laws


1
The Gas Laws!
  • Chemistry
  • Section 10-3

2
The Gas Laws
  • express mathematical relationships between
    volume, temperature, pressure, and amount of gas

3
Boyles Law
  • Volume is ??? proportional to pressure.
  • INVERSELY
  • P1.V1P2.V2
  • (assuming T and amt are constant)
  • Ex) p315 2 A gas has a pressure of 1.26 atm
    and occupies a volume of 7.40 L. If the gas is
    compressed to a volume of 2.93 L, what will the
    new pressure be?
  • ANS 3.18 atm

4
Be Careful!!
  • The following formulas ONLY apply when the
    temperature is in KELVIN!
  • Remember KoC273

5
Charles Law
  • Volume is ??? proportional to temperature.
  • DIRECTLY
  • V1/T1V2/T2
  • (assuming P and amt are constant)
  • Ex) p319 1A helium-filled balloon has a volume
    of 2.75 L at 20.oC. The volume of the balloon
    decreases to 2.46 L after it is placed outside on
    a cold day. What is the outside temperature in
    K? InoC?
  • ANS 262 K -11oC

6
Gay-Lussacs Law
  • Pressure is ??? proportional to temperature.
  • DIRECTLY
  • P1/T1P2/T2
  • (assuming V and amt are constant)
  • Ex) p320 2At 120.oC, the pressure of a sample
    of nitrogen is 1.07 atm. What will the pressure
    be if the temperature is raised to 205oC?
  • ANS 1.30 atm

7
The Combined Gas Law!
  • P1.V1/T1
  • P2.V2/T2
  • Notice that by holding ___ constant, we get
    Boyles Law.
  • TEMPERATURE
  • By holding ___ constant, we get Charles Law.
  • PRESSURE
  • By holding ___ constant, we get Gay-Lussacs Law.
  • VOLUME

8
The Combined Gas Law!
  • P1.V1/T1
  • P2.V2/T2
  • Lets practice!
  • p328 36,37,38
  • Shows the overall relationship between P, V, and
    T
  • (still assumes that amount is constant)
  • Temperature must still be in KELVIN!
  • Used to CONVERT
    CONDITIONS!

9
Daltons Law of Partial Pressures
  • The total pressure of a mixture of gases is
    equal to the sum of the partial pressures of all
    the component gases.
  • PT P1 P2 P3

10
One practical application
  • Collecting gas by water displacement (what does
    this mean?)
  • HINT We have done this in lab! (And we will do
    this in lab again!)
  • BUT, in reality the collected gas will never be
    pure! It will always be mixed with some water
    vapor.

11
More about water displacement
  • So, to get the pressure of the dry gas (without
    the water vapor)
  • Use the eudiometer like a barometer. Raise or
    lower the eudio until the water levels inside
    (meniscus) and outside the eudio are the same.
    Then the total gas pressure inside the eudio and
    the atmospheric pressure outside the eudio must
    be equal!

12
Even more about water displacement
  • Finally, using Daltons Law of P.P.
  • Patm Pgas PH2O
  • Patm read off of a barometer
  • PH2O look up in a table (Table A-8 p899) the
    water pressure varies with temp!
  • Pgas solve by subtracting!
  • Lets practice! p3251-2 p32842-43
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