The Behavior of
Gases
The Behavior of Gases
• The behavior of
gases rely
heavily on the
properties of
pressure,
temperature,
moles and
volume.
Think of Chem 1A….
• Mrs. Richards, Mr. Bannister, Ms. Knick,
Mrs. Olin, Mrs. Eberts…..
• What do you remember about gases????
Pressure & Force
• Pressure (P) is defined as the
force per unit of area on a
surface.
• Atmospheric pressure (atm)
is the pressure exerted on an
object due to the weight of the
column of the air above it in
the atmosphere.
• A barometer is a device used
to measure atmospheric
pressure.
Units of Pressure
• Pascal (Pa)
• millimeters of mercury (mm Hg)
• torr (torr)
• pounds per square inch (psi or lbs/in2)
• atmosphere (atm) - This is the unit of pressure that we will use
in chemistry. All pressure units must be converted to
atmospheres
Relationships between units of
pressure
• 1.0 atm = 760 mmHg
• 1.0 atm = 760 torr
• 1.0 atm = 1.0135 x 105 Pa
• 1.0 atm = 14.700 psi
PRACTICE: Convert 78.9 psi to units of atm.
Temperature
• A temperature is a
numerical measure of hot
and cold.
• We will measure or
calculate temperature in
units of Kelvin, not
Celsius.
• K = °C + 273.15
Example
• Convert 30
degrees C to
Kelvin
• Pretttyyy easy!!!
Volume
• A gas’ volume can
change; gases can
be compressed or
expanded.
• Units of liters (L).
• Remember, there
are 1000 mL in 1L.
Standard Temperature and
Pressure
• Abbreviated as STP
• Standard temperature is
equal to 0 °C, which is
273.15 K.
• Standard Pressure is 1
Atm
Direct Relationship vs. Inverse
Relationship
• Direct
Relationship: both
variables increase
together or both
variables decrease
together.
• Inverse
Relationship: one
variable increases
while the other
variable decreases
or vice versa.
The Gas Laws
Boyle’s Law: the pressure-volume relationship of gases
• Boyle’s Law states that the volume of a fixed mass of a
gas at a constant temperature varies inversely with its
pressure.
P1V1 = P2V2
Problem #1
A balloon filled with helium gas has a volume of
500 mL at a pressure of 1 atm. The balloon is
released into the air where the pressure is 0.5
atm. If the temperature has remained the same,
what volume does the gas occupy at this height?
On your own:
What pressure is required to compress
196.0 liters of air at 1.00 atmosphere into a
cylinder whose volume is 26.0 liters?
A gas occupies 12.3 liters at a pressure of
40.0 mm Hg. What is the volume when the
pressure is increased to 60.0 mm Hg?
(Watch the units!)
The Gas Laws
Charles’ Law: the Volume-Temperature relationship
• Charles’ Law states that the volume of a fixed mass of
gas held at a constant pressure varies directly with its
Kelvin temperature.
V1
T1
=
V2
T2
Problem #2
A gas has an initial volume of 752 mL at a
temperature of 25 degrees C. The gas is heated
to 100 degrees C. What is the new volume?
On your own….
Some students believe that teachers are full
of hot air. If I inhale 2.2 liters of gas at a
temperature of 18C and it heats to a
temperature of 38C in my lungs, what is the
new volume of the gas?
How hot will a 2.3 L balloon have to get to
expand to a volume of 400 L? Assume that
the initial temperature of the balloon is 25C.
The Gas Laws
Gay-Lussac’s Law: the pressure-temperature relationship
in gases
• Gay-Lussac’s Law states that the pressure of a fixed
mass of a gas held at a constant volume will vary directly
with its Kelvin temperature.
P1
T1
=
P2
T2
Problem #3
A gas has an initial temperature of 120 degrees C
with a pressure of 1.07 atm. The gas is heated
to a temperature of 205 degrees Celsius. What
is the new pressure?
On your own…
Determine the pressure change when a
constant volume of gas at 1.00 atm is
heated from 20.0 °C to 30.0 °C.
If a gas is cooled from 323.0 K to 273.15 K
and the volume is kept constant what final
pressure would result if the original pressure
was 750.0 atm?
The Gas Laws
The Combined Gas Law
• The combined gas law expresses the
relationship between pressure, volume, and the
Kelvin temperature of a fixed amount of gas.
(This means that the number of moles is held
constant)
P1V1
T1
=
P2V2
T2
Problem #4
V1 = 27.5 mL
V2 = ?
P1 = 0.974 atm
P2 = 0.993 atm
T1 = 22˚C
T2 = 15˚C
1. If 10L of oxygen at STP are heated to 512 ºC,
what will be the new volume of gas if the pressure
is also increased to 1520.0 mmHg?
2. What pressure is required to compress 196.0
liters of air at 1.00 atmosphere into a cylinder
whose volume is 26.0 liters?
3. A gas occupies 12.3 liters at a pressure of 40.0
mm Hg. What is the volume when the pressure is
increased to 60.0 mm Hg?
4. 2L of hydrogen, originally at 25.0 ºC and
750mmHg, is heated until a volume of 20L and a
pressure of 3.5 atm is reached. What is the new
temperature?
PDN:
A balloon is filled with 3.0 L of air at
STP is released into the air where
the temperature is 290K and the
pressure is 0.5 atm. What is the
volume of the balloon?
The Ideal Gas Law
• The ideal gas law is the mathematical
relationship among pressure, temperature,
volume, and the number of moles of a gas.
• PV = nRT
.
P = pressure
V = volume
n = # moles
R = ideal gas constant
T = Kelvin temperature
Problem #5
• Calculate the grams of CO2 that would
occupy a volume of 22.4 liters at STP.
On a new sheet of paper, use a
ruler…
Pressure
Balloon #1
Red
763.8 mm
Hg
Balloon #2 763.8 mm
Purple
Hg
Balloon #3 763.8 mm
Yellow
Hg
Balloon #4 763.8 mm
Orange
Hg
Volume
Temperature
27 C
27 C
27 C
27` C
Ideal Gas
Constant
moles
Grams
Diffusion & Effusion
• diffusion is the gradual mixing of two gases
due to their spontaneous, random motion
• effusion is the process by which molecules
of a gas confined in a container randomly
pass through a small opening in the
container