Chapter 16.3
The Gas Laws
Pressure and Volume (Boyle’s Law)
Temperature and Volume
(Charles’ Law)
Temperature and Pressure Law
Volume, temperature and pressure are
three different properties of a gas you
can measure.
Volume, temperature and pressure are
are related. How? The Gas Laws !
The three properties of a gas are:
Volume: The amount of space it takes up. The volume of
a gas will be the volume of its container.(Liters)
Temperature: The temperature of a gas is a measure of the
average kinetic energy of the moving particles. If the
particles are moving faster, their energy will be greater
and the temperature will be higher.
Pressure: The pressure of a gas is the force of its
outward push divided by the area of the walls of the
container. Measured in Pascals (Pa), atmospheres (atm),
pounds per square inch (psi)
The three properties of gases—volume, temperature and
pressure—are all related.
Boyle’s Law
Robert Boyle (1627-1691)
Boyle conducted pioneering
experiments in studying the
role of air in combustion,
respiration, and the
transmission of sound. In
1662, Boyle published what is
now known as Boyle's law:
At constant temperature the
volume of a gas is inversely
proportional to the pressure.
• What does this mean in words?
• V  P  If the volume goes up then the pressure
goes down. The particles have to travel further
and hit the containers wall less often.
• V  P  If the volume goes down then the
pressure goes up. The particles have to travel less
far and hit the containers wall more often.
The mathematical form of Boyle's Law is:
V1P1 = V2 P2
V1 = intial volume
P1 = intial pressure
V2 = final volume
P2 = final pressure
P and V Changes
P1
V1
P2
V2
• In this diagram you can see that more mass is added to the top of
the plunger at each stage. The more mass, the more the gas is
compressed. The same number of gas particles are trapped in an
increasingly smaller space, which increases the pressure of the gas
on the walls of the container.
Boyles Law Practice
Solve this problem
Initial conditions
Final conditions
P1
= 50 pascals P2
= 200 pascals
V1
= 1.5 L
= ?
V2
?
Charles Law
Jacques Charles (1746-1823)
The physical principle known as Charles’ Law states
that raising the temperature of a gas increases
its volume; lowering the temperature of a gas
decreases its volume.
Charles’ Law: V and T
At constant pressure, the volume of a gas is
directly related to its absolute (K) temperature
T
V
T
V
Charles Law Formula
V1
T1
= V2
T2
Remember the temp
is measured in K
°C + 273 = K
In both parts of this diagram the gas is at the same
pressure, but you can see that the temperature has
risen from –65°C to 250°C. The gas particles
move faster at higher temperatures and collide
more often. The same number of gas particles now
take up a larger space.
Charles’ Law Practice
V = 125 mL
V = 250 mL
T = 273 K
T = ?
Observe the V and T of the balloons. How
does volume change with temperature?
Note to self. Check balloon in freezer.
Another Practice Problem
A balloon has a volume of
785 mL on a Fall day when
the temperature is 21°C. In
the winter, the gas cools to
0°C. What is the new volume
of the balloon?
Gay-Lussac’s Law:
Pressure-Temperature Law
The pressure exerted by a confined gas
is directly related to the temperature
(Kelvin) at constant volume.
T
P
T
P
Very much like Charles Law! (T
and V)
Pressure Temperature Law
P1
T1
= P2
T2
P T Problem
A gas has a pressure at 2.0 atm at 18°C.
What will be the new pressure if the
temperature rises to 62°C?
T = 18°C
T = 62°C
Learning Check
Complete with 1) Increases 2) Decreases
3) Does not change
A. Pressure _____, when V decreases
B. When T decreases, V _____.
C. Pressure _____ when V changes from 12.0 L
to 24.0 L
D. Volume _____when T changes from 15.0 °C to
45.0°C
Solving gas law problems
•
•
•
•
What information do they give me? (2)
What are they looking for? (1)
Which of the three formulas applies?
Plug in numbers and solve.
THE END