GAS LAWS
How are each of the following related?
1) Pressure and Temperature2) Pressure and Volume
4) Temperature and Volume
3) Pressure and Amount of Gas
*Consider all other variables constant. Come up with an example which confirms your hypothesis.
5) Volume and Amount of Gas
Factors Affecting Pressure
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
1 atm = 101.325 kPa = 760 torr = 760 mmHg = 14.7 psi atm = atmospheres
kPa = kilopascals torr = torr
mmHg = millimeters of mercury psi = pounds per square inch
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
If the temperature is constant, as pressure of a gas increases the volume decreases.
PV = K P1V1 = P2V2
Example: A ballon contains 30.0 L of helium 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
If the pressure is constant, as temperature of a gas increases the volume increases.
*Temperature must be in Kelvin for all gas laws*
V= K V1 = V2
T T1 T2
Year: 1787
Example: A balloon inflated in a room at 240C
has a volume of 4.00L. The balloon is then heated to a temperature of 580C. What is
the new volume if the pressure remains constant?
*To get from 0C to
Gay-Lussac’s Law
As the temperature of an enclosed gas increases, the pressure increases at constant volume.
P= K P1 = P2
T T1 T2
Year: 1802
Example: The gas in a used aerosol can is at a pressure of 103 kPa at 250C. If the can is
thrown onto a fire, what will the pressure be when the temperature reaches 9280C?
*To get from 0C to
Combined Gas Law
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?
PV= K P1V1 = P2V2
T T1 T2
Freddie Mercury
Ideal Gas Law
PV = nRTThe 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
mol*K R = 8.31 L*kPamol*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
Ideal vs. Real Gases
In order to behave as an ideal gas, gases could not have any volume and could beattracted 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
Graham’s Law of effusion
Year: 1840 Diffusion: The tendency of molecules to move
toward areas of lower concentration until the concentration is uniform throughout.
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