1. Diffusion
Particles of 2 or more substances mix spontaneously due to random motion How fast gases diffuse depends on: 1. speed of particles (KE) 2. Size of particles 3. attractive forces between particles
Effusion
Gas particles leaving a container through a small opening
Movement caused by pressure

2. Pressure Can be used as conversion factors. Collisions on a surface
1 atm = 760 mm Hg = 760 torr = kPa
Can be used as conversion factors.
760 mm Hg
760 torr
1 atm
760 mm Hg
760 torr
kPa

3. Sample Problem A
The average atmospheric pressure in Denver, Colorado is atm. Express this pressure in millimeters of mercury (mm Hg).

4. Sample Problem B
The average atmospheric pressure in Denver, Colorado is 631 mm Hg. Express this pressure in kPa.

5. Temperature Measure of the average kinetic energy of the molecules
MUST ALWAYS be in Kelvin (K)
ALWAYS!
SERIOUSLY!
K = ° C + 273

6. Combined Gas Law It’s a Before-After equation
Look for words like “starts”, “begins”, “initial”, etc…
Look for words like “ends”, “final”, “change”, etc…
Look for the units to be mentionned twice
Units don’t matter so long as they match
EXCEPT for Temperature = Kelvin (K)

7. Combined Gas Law = P1 V1 T1 P2 V2 T2
P = Pressure (atm, mm Hg, torr, kPa)
V = Volume (mL or L)
T = Temperature (K)

8. Sample Problem C
A helium-filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10.0°C?

9. Sample Problem D
A balloon has a volume of 40.0 L at 20 °C and atm. At what temperature will the balloon expand to L and 1.00 atm?

10. Boyle’s Law An equation Temperature is constant P1 V1 = P2 V2
When P increases, V decreases
When P decreases, V increases
Inversely proportional relationship

11. Sample Problem E
A sample of oxygen gas has a volume of mL when its pressure is atm. What will the volume of the gas be at a pressure of atm if the temperature remains constant?

12. Charles’ Law An equation Pressure is constant V1 = V2 T1 T2
When T increases, V increases
When T decreases, V decreases
Directly proportional

13. Sample Problem F
A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at 50°C if the pressure remains constant?

14. Gay-Lussac’s Law An equation Volume is constant P1 = P2 T1 T2
When T increases, P increases
When T decreases, P decreases
Directly proportional

15. Sample Problem G
The gas in a container is at a pressure of atm at 25°C. Directions on the container warn the user not to keep it in a place where the temperature exceeds 52°C. What would the gas pressure in the container be at 52°C?

16. A Summary
All came from …

17. Ideal Gas Doesn’t really exist
Exists with low numbers of molecules, high temp
Explained by the Kinetic Molecular Theory

18. 5 Assumptions of the Kinetic Molecular Theory
Gases molecules are far apart.
Gas molecules collide w/o losing energy.
Gas molecules have kinetic energy because they move in constant, random motion
There are no attraction / repulsion forces.

19. 5 Assumptions of the Kinetic Molecular Theory
Kinetic energy depends on T.
Higher NRG  more KE  higher T
At same T, all gas molecules of the same mass have exactly the same KE
At same T, lighter gas molecules KE > heavier gas molecules KE

20. Ideal Gas Law Assuming all these to be true … P V = n R T
P = pressure (atm)
V = volume (L)
n = # of mol
R = L atm / mol K
T = Temperature (K)

21. When Do I Use It? The variables are only mentionned ONCE.
There has been no change in anything!

22. Sample Problem A
What is the pressure in atmospheres exerted by a mol sample of nitrogen gas in a 10.0 L container at 298 K?