Chapter 14 in Prentice Hall Chemistry

*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

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.

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

PV = K P
1
V
1
= P
2
V
2
If the temperature is constant, as pressure of a gas increases the volume decreases.
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?
Year: 1662

V= K V
1
= V
2
T T
1
T
2
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 24 0 C has a volume of 4.00L. The balloon is then heated to a temperature of 58 0 C. What is the new volume if the pressure remains constant?
*To get from 0 C to
K, add 273

P= K P
1
= P
2
T T
1
T
2
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 pressure of 103 kPa at 25 0 C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 0 C?
*To get from 0 C to
K, add 273

PV= K P
1
V
1
= P
2
V
2
T T
1
T
2
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?
Freddie
Mercury

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 mol*K
R = 8.31 L*kPa mol*K
Example : A deep underground cavern contains 2.24 x 10 6 L of CH
4
gas at a pressure of 1.50 x 10 3 kPa and a temperature of 42 0 C. How many moles of CH
4
gas does the cavern contain?

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?

In a mixture of gases, the total pressure is the sum of the partial pressures of the gases at constant temperature.
P total
= P
1
+ P
2
+ P
3
+ ...
Example : Air contains O
2
, N
2
, CO
2
, and trace amounts of other gases. What is the partial pressure of O
2
at 101.30 kPa of total pressure if the partial pressures of N
2
, CO
2
, and other gases is
79.10 kPa, 0.040 kPa, and 0.94 kPa, respectively?

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