Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
118 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
Explaining the behavior of gases The kinetic-molecular theory
explains the following behavior of gases.
• Low density Density is a measure of mass per unit volume. The
difference between the high density of a solid and the low density
of a gas is due mainly to the large amount of space between the
particles in the gas. There are fewer particles in a gas than in a
solid of the same volume.
• Compression and expansion A gas will expand to fill its container. Thus, the density of a sample of gas will change with the
volume of the container it is placed in. The gas will become more
dense as it is compressed into a smaller container. The gas will
become less dense as it expands in a larger container.
• Diffusion Gas particles flow past each other easily because there
are no significant forces of attraction between them. Diffusion
refers to the movement of one material through another, such as
when one gas flows into a space already occupied by another gas.
The rate of diffusion depends mostly on the mass of the particles.
Lighter particles diffuse more quickly than heavier particles.
Because lighter particles have the same average kinetic energy as
do heavier particles at the same temperature, lighter particles must
have, on average, a greater velocity.
• Effusion If you have ever seen a tire deflate from a puncture, you
are familiar with effusion. Effusion is the escape of a gas through
a small opening in its container. Graham’s law of effusion states
that the rate of effusion for a gas is inversely proportional to the
square root of its molar mass.
Rate of effusion ؔ
Using Graham’s law, you can also compare the rates of diffusion for
two gases.
ϭ
Ί
ᎏ
m
m
o
o
l
l
a
a
r
r
m
m
a
a
s
s
s
s
A
B
ᎏ
Rate A
ᎏ
Rate B
1
ᎏᎏ
͙molar ෆmass ෆ
▲
118 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
Explaining the behavior of gases The kinetic-molecular theory
explains the following behavior of gases.
• Low density Density is a measure of mass per unit volume. The
difference between the high density of a solid and the low density
of a gas is due mainly to the large amount of space between the
particles in the gas. There are fewer particles in a gas than in a
solid of the same volume.
• Compression and expansion A gas will expand to fill its container. Thus, the density of a sample of gas will change with the
volume of the container it is placed in. The gas will become more
dense as it is compressed into a smaller container. The gas will
become less dense as it expands in a larger container.
• Diffusion Gas particles flow past each other easily because there
are no significant forces of attraction between them. Diffusion
refers to the movement of one material through another, such as
when one gas flows into a space already occupied by another gas.
The rate of diffusion depends mostly on the mass of the particles.
Lighter particles diffuse more quickly than heavier particles.
Because lighter particles have the same average kinetic energy as
do heavier particles at the same temperature, lighter particles must
have, on average, a greater velocity.
• Effusion If you have ever seen a tire deflate from a puncture, you
are familiar with effusion. Effusion is the escape of a gas through
a small opening in its container. Graham’s law of effusion states
that the rate of effusion for a gas is inversely proportional to the
square root of its molar mass.
Rate of effusion ؔ
Using Graham’s law, you can also compare the rates of diffusion for
two gases.
ϭ
Ί
ᎏ
m
m
o
o
l
l
a
a
r
r
m
m
a
a
s
s
s
s
A
B
ᎏ
Rate A
ᎏ
Rate B
1
ᎏᎏ
͙molar ෆmass ෆ
▲