1. Graham’s Law of effusion
Review
Notes on Graham’s law of effusion
Guided practice

2. Combined Gas Law
P1V1T2 = P2V2T1

3. Ideal Gas Law
PV = nRT

4. ST: 273 K SP: 1 atm, 760 torr, 760 mmHg, 101.3 kPa
STP Conditions
ST: 273 K
SP: 1 atm, 760 torr, 760 mmHg, kPa

5. Values of R with Constants
0.0821atm*L/k*mol
62.4mmHg*L/K*mol and 62.4torr*L/K*mol
8.31kPa*L/k*mol

6. Dalton’s Law of Partial Pressure
PT = P1 + P2 + P3 …

7. Graham’s Law of Effusion
Notes

8. Diffusion vs. Effusion vs. Osmosis
Diffusion: the natural tendency of gas to spread out to uniformly fill the area.
Cookies baking can be smelled throughout the house.
Effusion: the process in which a gas flows through a small hole in a container.
Balloons deflate over time
Osmosis: the ability of water to flow through a semi permeable membrane to equalize concentrations

9. Graham’s Law of Effusion
Is there a way to predict how long it will take to effuse?
That’s what Graham determined.
Must relate one gas to another.
Thought: who can get up and move faster? Little kids or their grandparents?
Same thing for gases – the lighter/smaller the faster!

10. Rate of effusion = MMB MMA
MMB the molar mass of the heaviest compound.
MMA the molar mass of the lightest compound.

11. Relating rate to time MMB = TimeB MMA TimeA
Because B weighs more, it will take longer for it to get moving.

12. Relating rate to volume
MMB = VolumeA
MMA VolumeB
Since A moves the fastest and is small enough to escape, more of A will get out than B.

13. What is the rate of effusion of He to N2?
MM of He = 4g/mol
MM of N2 = 28g/mol 28 =
Meaning He effuses times faster than N2.
2.646

14. Why are the rates of CO & N2 the same?
They have the same molar mass!

15. Which effuses faster, H2 or Cl2? How much faster?
MM H2 = 2g/mol
MM Cl2 = 70.9g/mol
Therefore H2 effuses faster! = 2
5.954

16. If it takes 90s for Ar to effuse, how long will it take Cl2?
MM = 40
MM = 70.9
MMB = TimeB MMA TimeA 70.9 = X = X/ sec = X

17. If 10.5 mL of an unknown gas effuses in the same amount of time as it takes 15.7 mL of F2 to effuse, what is the MM of the unknown gas?
MMB = VolumeA
MMA VolumeB
Since fluorine has more volume escaping it is A – always want ratios set up to be greater than 1
X = 15.7
X/38 =
X/38 =
X = 38 ( ) = g/mol