GAS LAWS
Chapter 14 in Prentice Hall Chemistry
BELLWORK
How are each of the following related?
*Consider all other variables constant. Come up with an example which confirms your hypothesis.
1) Pressure and Temperature
2) Pressure and Volume
3) Pressure and Amount of Gas
4) Temperature and Volume
5) Volume and Amount of Gas
Factors Affecting Pressure
David Bowie
Amount of Gas: Increasing the number of particles increases collisions,
which increases pressure. Removing particles reduces pressure.
Volume: Increasing the volume will decrease the pressure of a gas since
collisions are less likely. Decreasing the volume has the opposite effect.
Temperature: Increasing the temperature increases the speed of the
molecules, which leads to more collisions and greater pressure.
Decreasing the temperature has the opposite effect.
Units of Pressure
atm = atmospheres
kPa = kilopascals
torr = torr
mmHg = millimeters of mercury
psi = pounds per square inch
1 atm = 101.325 kPa = 760 torr = 760 mmHg = 14.7 psi
Units can easily be converted from one to another by using
dimensional analysis.
Example: 0.89 atm = 760 torr = 676.4 torr
1 atm
Boyle’s Law
PV = K
P1V1 = P2V2
If the temperature is constant, as pressure
of a gas increases the volume decreases.
Example: A ballon contains 30.0 L of helium Year: 1662
gas at 103 kPa. What is the volume of the
helium when the balloon rises to an altitude
where the pressure is only 25.0 kPa, assuming
constant temperature?
Charles’s Law
V= K
T
V1 = V2
T1 T2
If the pressure is constant, as temperature of a
gas increases the volume increases.
*Temperature must be in Kelvin for all gas laws*
Year: 1787
Example: A balloon inflated in a room at 240C *To get
has a volume of 4.00L. The balloon is then from 0C to
heated to a temperature of 580C. What is K, add 273
the new volume if the pressure remains
constant?
Gay-Lussac’s Law
P= K
T
P1 = P2
T1 T2
As the temperature of an enclosed gas increases,
the pressure increases at constant volume.
Year: 1802
Example: The gas in a used aerosol can is at a *To get
0C to
0
from
pressure of 103 kPa at 25 C. If the can is
thrown onto a fire, what will the pressure be K, add 273
when the temperature reaches 9280C?
Combined Gas Law
PV= K
T
The combined gas law allows you to do
calculations for situations in which only the
amount of gas is constant.
Example: The volume of a gas filled balloon is
30.0 L at 313 K and 153 kPa. What would the
volume be at STP?
P1V1 = P2V2
T1
T2
Freddie
Mercury
Ideal Gas Law
PV = nRT
The moles of gas is no longer a constant, and is now
represented by “n”. There is also a gas constant, “R”.
The gas constant depends on the unit for pressure.
R = 0.0821 L*atm
R = 8.31 L*kPa
mol*K
mol*K
Example: A deep underground cavern contains 2.24 x 106 L
of CH4 gas at a pressure of 1.50 x 103 kPa and a
temperature of 420C. How many moles of CH4 gas does
the cavern contain?
Ideal vs. Real Gases
In order to behave as an ideal gas, gases
could not have any volume and could be
attracted to other gas molecules.
This is impossible, however, under certain conditions
real gases can behave very similarly to an ideal gas.
Real gases differ most from an ideal gas
at low temperatures and high pressures.
Checkpoint: Why are real and ideal gases different under
these conditions?
Dalton’s Law of Partial Pressure
In a mixture of gases, the total pressure is
the sum of the partial pressures of the gases
at constant temperature.
Ptotal= P1 + P2 + P3 + ...
Example: Air contains O2, N2, CO2, and trace amounts of other
gases. What is the partial pressure of O2 at 101.30 kPa of total
pressure if the partial pressures of N2, CO2, and other gases is
79.10 kPa, 0.040 kPa, and 0.94 kPa, respectively?
Graham’s Law of effusion
Diffusion: The tendency of molecules to move
toward areas of lower concentration until the
concentration is uniform throughout.
Year: 1840
Effusion: A gas escapes through a tiny hole in a container
Gases of lower molar mass diffuse and effuse
faster than gasses of higher molar mass.
There are equations which describe this phenomena, but we
will not cover them in this class.
CrashCourse Chemistry: Ideal Gas Law
http://www.youtube.com/watch?v=BxUS1K7xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr