14.4
Gases: Mixtures and Movements
A list of gear for an expedition
to Mount Everest includes
climbing equipment, ski
goggles, a down parka with a
hood, and most importantly
compressed-gas cylinders of
oxygen. You will find out why
a supply of oxygen is
essential at higher altitudes.
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14.4
Gases: Mixtures and Movements > Dalton’s Law
Dalton’s Law
How is the total pressure of a mixture of
gases related to the partial pressures of
the component gases?
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14.4
Gases: Mixtures and Movements > Dalton’s Law
The contribution each gas in a mixture makes to
the total pressure is called the partial pressure
exerted by that gas.
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14.4
Gases: Mixtures and Movements > Dalton’s Law
Dalton’s law of partial pressures states
that, 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.
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14.4
Gases: Mixtures and Movements > Dalton’s Law
Three gases are combined in container T.
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Gases: Mixtures and Movements > Dalton’s Law
The partial pressure of oxygen must be 10.67
kPa or higher to support respiration in humans.
The climber below needs an oxygen mask and a
cylinder of compressed oxygen to survive.
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SAMPLE PROBLEM 14.6
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SAMPLE PROBLEM 14.6
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SAMPLE PROBLEM 14.6
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SAMPLE PROBLEM 14.6
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Practice Problems for Sample Problem 14.6
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14.4
Gases: Mixtures and Movements > Graham’s Law
Graham’s Law
How does the molar mass of a gas
affect the rate at which the gas
effuses or diffuses?
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14.4
Gases: Mixtures and Movements > Graham’s Law
Diffusion is the tendency of molecules to move
toward areas of lower concentration until the
concentration is uniform throughout.
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14.4
Gases: Mixtures and Movements > Graham’s Law
Bromine vapor is
diffusing upward
through the air in a
graduated cylinder.
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14.4
Gases: Mixtures and Movements > Graham’s Law
After several hours,
the bromine has
diffused almost to
the top of the
cylinder.
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14.4
Gases: Mixtures and Movements > Graham’s Law
During effusion, a gas escapes through a tiny
hole in its container.
Gases of lower molar mass diffuse and
effuse faster than gases of higher
molar mass.
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14.4
Gases: Mixtures and Movements > Graham’s Law
Thomas Graham’s Contribution
Graham’s law of effusion states that the rate of
effusion of a gas is inversely proportional to the
square root of the gas’s molar mass. This law
can also be applied to the diffusion of gases.
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Gases: Mixtures and Movements > Graham’s Law
Comparing Effusion Rates
A helium filled balloon will deflate sooner than an
air-filled balloon.
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14.4
Gases: Mixtures and Movements > Graham’s Law
Helium atoms are less massive than oxygen or
nitrogen molecules. So the molecules in air move
more slowly than helium atoms with the same
kinetic energy.
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14.4
Gases: Mixtures and Movements > Graham’s Law
Because the rate of effusion is related only to a
particle’s speed, Graham’s law can be written as
follows for two gases, A and B.
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14.4
Gases: Mixtures and Movements > Graham’s Law
Helium effuses (and diffuses) nearly three times
faster than nitrogen at the same temperature.
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14.4 Section Quiz.
1. What is the partial pressure of oxygen in a
diving tank containing oxygen and helium if
the total pressure is 800 kPa and the partial
pressure of helium is 600 kPa?
a. 200 kPa
b. 0.75 kPa
c. 1.40 104 kPa
d. 1.33 kPa
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14.4 Section Quiz.
2. A mixture of three gases exerts a pressure of
448 kPa, and the gases are present in the
mole ratio 1 : 2 : 5. What are the individual
gas pressures?
a. 44 kPa, 88 kPa, and 316 kPa
b. 52 kPa, 104 kPa, and 292 kPa
c. 56 kPa, 112 kPa, and 280 kPa
d. 84 kPa, 168 kPa, and 196 kPa
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14.4 Section Quiz.
3. Choose the correct words for the spaces.
Graham's Law says that the rate of diffusion
of a gas is __________ proportional to the
square root of its _________ mass.
a. directly, atomic
b. inversely, atomic
c. inversely, molar
d. directly, molar
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