3.2 The Gas Laws
When you inhale, the volume of
your chest cavity increases, and
air moves into your lungs. When
you exhale, the volume of your
chest cavity decreases, and air is
pushed out of your lungs.
Changes in the volume, the
temperature, the pressure, and
the number of particles have
predictable effects on the behavior
of a gas.
3.2 The Gas Laws
What causes gas pressure in a closed
container?
Pressure is the result of a force distributed over
an area.
Pressure
Collisions between particles of a gas and the
walls of the container cause the pressure in
a closed container of gas.
3.2 The Gas Laws
A moving hockey puck exerts pressure on
any object it hits. A layer of shatterproof glass
protects spectators.
• The faster the puck is traveling, the greater the
force of the puck on the glass. A greater force
means more pressure.
• The smaller the area of impact is, the greater
the pressure. If the edge of the puck hits the
glass, it exerts more pressure than if the face of
the puck hits the glass.
Pressure
3.2 The Gas Laws
The SI unit of pressure is derived from SI
units for force and area.
• Force is measured in newtons (N).
• Area is measured in square meters (m2).
• The SI unit for pressure, the pascal (Pa), is
shorthand for newtons per square meter.
• Scientists often express larger amounts of
pressure in kilopascals. One kilopascal (kPa) is
equal to 1000 pascals.
Pressure
3.2 The Gas Laws
The helium atoms in a balloon are constantly
moving. There are more than 1022 helium
atoms in a small balloon.
• When many particles collide with the walls of a
container at the same time, they produce a
measurable pressure.
• The more frequent the collisions, the greater
the pressure is.
• The speed of the particles and their mass also
affect the pressure.
Pressure
3.2 The Gas Laws
What factors affect gas pressure?
Factors That Affect Gas Pressure
Factors that affect the pressure of an
enclosed gas are its temperature, its volume,
and the number of its particles.
3.2 The Gas Laws
Factors That Affect Gas Pressure
Raising the temperature of a gas will
increase its pressure if the volume of the
gas and the number of particles are
constant.
Temperature
3.2 The Gas Laws
The firefighter is using a
pressure gauge to check
the air pressure in a tire
on a firetruck.
If he checks the tire
pressure again after a
long drive on a highway,
he will find that the
pressure has increased.
Factors That Affect Gas Pressure
3.2 The Gas Laws
The motion of tires on the highway heats the
tires and increases tire pressure.
• As the temperature rises, the average kinetic
energy of the particles in the air increases.
• With increased kinetic energy, the particles
move faster and collide more often with the
inner walls of the tires.
• Faster-moving particles hit the walls with
greater force.
• More collisions and increased force cause the
pressure of the air in the tires to rise.
Factors That Affect Gas Pressure
3.2 The Gas Laws
Factors That Affect Gas Pressure
Reducing the volume of a gas increases its
pressure if the temperature of the gas and
the number of particles are constant.
Volume
3.2 The Gas Laws
Twist the cap onto a plastic bottle and then
squeeze it. What happens?
• The volume of the plastic bottle begins to
decrease.
• As the volume decreases, the particles of
trapped air collide more often with the walls of
the bottle.
• The pressure in the bottle increases.
Factors That Affect Gas Pressure
3.2 The Gas Laws
Movement of a muscle called the diaphragm
changes the volume of your chest cavity.
• The volume increases when you inhale. The pressure
decreases and air flows to your lungs.
• The volume decreases when you exhale. The pressure
increases and air flows from your lungs.
Factors That Affect Gas Pressure
Lungs
Rib Cage
Diaphragm
Inhaling Exhaling
Diaphragm
contracts. Rib
cage is lifted
up and out.
Diaphragm
relaxes. Rib
cage moves
down and in.
3.2 The Gas Laws
Factors That Affect Gas Pressure
Increasing the number of particles will
increase the pressure of a gas if the
temperature and the volume are constant.
The more particles there are in the same
volume, the greater the number of collisions and
the greater the pressure.
Number of Particles
3.2 The Gas Laws
French physicist Jacques Charles collected
data on the relationship between the
temperature and volume of gases. The
graph of the data showed a direct
relationship between the volume of a gas
and the temperature of the gas.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
Charles extended the
graph beyond the
measured data to find
the temperature that
would produce a
volume of 0 L.
•The temperature at the
point where the line
crossed the x-axis was
–273.15°C.
Charles’s Law
3.2 The Gas Laws
•This temperature is equal to 0 K on the
Kelvin temperature scale.
•A temperature of 0 K is called absolute
zero.
Charles’s Law
3.2 The Gas Laws
Charles’s law states that the volume of a
gas is directly proportional to its temperature
in kelvins if the pressure and the number of
particles of the gas are constant.
T1 and V1 represent the temperature and
volume of a gas before a change occurs. T2
and V2 represent the temperature and
volume after a change occurs.
Charles’s Law
3.2 The Gas Laws
Robert Boyle described
the relationship between
the pressure and volume
of a gas. The graph
shows an inverse
relationship between the
volume of a gas and the
pressure of the gas.
Boyle’s Law
3.2 The Gas Laws
Robert Boyle described
the relationship between
the pressure and volume
of a gas. The graph
shows an inverse
relationship between the
volume of a gas and the
pressure of the gas.
Boyle’s Law
3.2 The Gas Laws
Robert Boyle described
the relationship between
the pressure and volume
of a gas. The graph
shows an inverse
relationship between the
volume of a gas and the
pressure of the gas.
Boyle’s Law
3.2 The Gas Laws
Robert Boyle described
the relationship between
the pressure and volume
of a gas. The graph
shows an inverse
relationship between the
volume of a gas and the
pressure of the gas.
Boyle’s Law
3.2 The Gas Laws
Boyle’s law states that the volume of a gas
is inversely proportional to its pressure if the
temperature and the number of particles are
constant.
P1 and V1 represent the pressure and
volume of a gas before a change occurs. P2
and V2 represent the pressure and volume
of a gas after a change occurs.
Boyle’s Law
3.2 The Gas Laws
The relationships described by Boyle’s law
and Charles’s law can be described by a
single law. The combined gas law describes
the relationship among the temperature,
volume, and pressure of a gas when the
number of particles is constant.
The Combined Gas Law
3.2 The Gas Laws
The Combined Gas Law
A cylinder that contains air at a pressure
of 100 kPa has a volume of 0.75 L. The
pressure is increased to 300 kPa. The
temperature does not change. Find the
new volume of air.
The Combined Gas Law
3.2 The Gas Laws
Read and Understand
What information are you given?
The Combined Gas Law
3.2 The Gas Laws
Read and Understand
What information are you given?
P1 = 100 kPa P2 = 300 kPa V1 = 0.75 L
The Combined Gas Law
3.2 The Gas Laws
Plan and Solve
What unknown are you trying to
calculate?
What expression can you use?
The Combined Gas Law
3.2 The Gas Laws
Plan and Solve
What unknown are you trying to
calculate?
What expression can you use?
The Combined Gas Law
3.2 The Gas Laws
Plan and Solve
Cancel out the variable that does not change
and rearrange the expression to solve for V2.
Replace each variable with its known value.
The Combined Gas Law
3.2 The Gas Laws
Plan and Solve
Cancel out the variable that does not change
and rearrange the expression to solve for V2.
Replace each variable with its known value.
The Combined Gas Law
3.2 The Gas Laws
Look Back and Check
Is your answer reasonable?
The Combined Gas Law
3.2 The Gas Laws
Look Back and Check
Is your answer reasonable?
Volume should decrease as pressure
increases. The pressure tripled from 100 kPa
to 300 kPa. The answer, 0.25 L, is one third the
original volume, 0.75 L.
The Combined Gas Law
3.2 The Gas Laws
1. A gas has a volume of 5.0 L at a pressure
of 50 kPa. What happens to the volume
when the pressure is increased to 125 kPa?
The temperature does not change.
The Combined Gas Law
3.2 The Gas Laws
2. Gas stored in a tank at 273 K has a
pressure of 388 kPa. The safe limit for the
pressure is 825 kPa. At what temperature
will the gas reach this pressure?
The Combined Gas Law
3.2 The Gas Laws
3. At 10ºC, the gas in a cylinder has a
volume of 0.250 L. The gas is allowed to
expand to 0.285 L. What must the final
temperature be for the pressure to remain
constant? (Hint: Convert from degrees
Celsius to kelvins using the expression ºC +
273 = K.)
The Combined Gas Law
3.2 The Gas Laws
Balloons like this one are
used by scientists to
gather data about Earth’s
atmosphere. The balloon is
filled with hydrogen or
helium. It carries a
package of weather
instruments up into the
atmosphere.
The Combined Gas Law
3.2 The Gas Laws
The gas laws explain the
behavior of the gas in the
balloon.
The Combined Gas Law
3.2 The Gas Laws
Assessment Questions
1. What causes the pressure to increase if more gas
particles are added to a closed container?
a. an increase in the number of collisions between the gas
and the container walls
b. a decrease in the volume of the container
c. a decrease in the size of each particle as the number of
particles increases
d. an increase in the number of collisions between air
particles and the outside of the container
3.2 The Gas Laws
Assessment Questions
1. What causes the pressure to increase if more gas
particles are added to a closed container?
a. an increase in the number of collisions between the gas
and the container walls
b. a decrease in the volume of the container
c. a decrease in the size of each particle as the number of
particles increases
d. an increase in the number of collisions between air
particles and the outside of the container
ANS: A
3.2 The Gas Laws
Assessment Questions
2. When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease?
a. increase in air temperature
b. decrease in the balloon's volume
c. decrease in the number of air particles as they leaked out of the balloon
d. a chemical reaction between the air particles and the balloon
3.2 The Gas Laws
Assessment Questions
2. When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease?
a. increase in air temperature
b. decrease in the balloon's volume
c. decrease in the number of air particles as they leaked out of the balloon
d. a chemical reaction between the air particles and the balloon
ANS: C
3.2 The Gas Laws
Assessment Questions
3. A gas has a volume of 15 L, a temperature of
300 K, and an unknown initial pressure. Then, the
gas expands to 30 L, remains at 300 K, and has a
pressure of 300 kPa. What was the initial pressure
of the gas?
a. 150 kPa
b. 600 kPa
c. 330 kPa
d. 570 kPa
3.2 The Gas Laws
Assessment Questions
3. A gas has a volume of 15 L, a temperature of
300 K, and an unknown initial pressure. Then, the
gas expands to 30 L, remains at 300 K, and has a
pressure of 300 kPa. What was the initial pressure
of the gas?
a. 150 kPa
b. 600 kPa
c. 330 kPa
d. 570 kPa
ANS: B
3.2 The Gas Laws
Assessment Questions
4. According to Charles’s law, the relationship
between the temperature and the volume of a gas
is
a. direct.
b. inverse.
c. exponential.
d. inverse square.
3.2 The Gas Laws
Assessment Questions
4. According to Charles’s law, the relationship
between the temperature and the volume of a gas
is
a. direct.
b. inverse.
c. exponential.
d. inverse square.
ANS: A
3.2 The Gas Laws
Assessment Questions
1. When the temperature of the gas in closed
container is increased, the pressure increases.
True
False
3.2 The Gas Laws
Assessment Questions
1. When the temperature of the gas in closed
container is increased, the pressure increases.
True
False
ANS: T
