1. Warm-Up 12/14/2016
How many moles of nitrogen are in 135 L of nitrogen gas at Standard Temperature and Pressure(STP)?
A) 4.82 moles of N2
B) 5.53 moles of N2
C) 6.02 moles of N2
D) moles of N2

2. Dalton’s Law of Partial Pressure Continued
So what if we said:
ntotal = n1 + n2 + n3 + ….
If each of the gases obeys the ideal gas equation, we can write :
P1 = n1 (RT/V) , P2 =n2(RT/V), P3= n3 (RT/V)
Ptotal = ( n1 + n2 + n3 + ….) (RT/V) = ntotal(RT/V)

3. Practice
A gaseous mixture made from 6.00 g O2 and g CH4 is placed in a 15.0 L vessel at 0˚ C. What is the partial pressure of each gas, and what is the total pressure in the vessel

4. Practice
What is the total pressure exerted by a mixture of 2.00 grams of H2 and 8.00 grams of N2 at 273 K in a 10.0 L vessel?

5. Collection of Gas by Water Displacement
Gases are often collected by bubbling them through water
This is known as “collecting a gas by water displacement”
The total pressure is equal to the gas’s pressure plus the pressure of the water vapor
Ptotal = Pgas + Pwater vapor(H2O)

7. Example Problem
A quantity of gas is collected over water at 8°C in a 353 cm3 vessel. The manometer indicates a pressure of 84.5 kPa. What is the pressure of the gas if the vapor pressure of water at 8°C is 1.1 kPa?
Ans) kPa

8. Example # 2
A 450 cm3 sample of hydrogen is collect over water at 12oC.   The pressure of the hydrogen and water vapor mixture is 78.5 kPa.  What is the partial pressure of the dry hydrogen gas? Water vapor pressure at 12 ° C is kPa

9. Graham’s Law Diffusion is the random scattering of gas molecules
It is the mixing of gas molecules
Diffusion occurs when molecules migrate from areas of high concentration to areas of low concentration
Example: If a bottle of ammonia is open, you will soon smell the ammonia due to the diffusion of gaseous ammonia particles

10. Graham’s Law Continued
Graham determined a law that allows for the rate of effusion to be measured
Effusion occurs when gas molecules escape from a small hole in the gas’s container
Graham found that the rate of effusion of a gas is inversely proportional to the square root of its molar mass

11. Diffusion and Effusion

12. Graham’s Law Continued
The larger a particle’s mass, the slower the particle will effuse
Graham’s Law is:
Rate B molar mass gas A
Rate A molar mass gas B =

13. Example #1
What is the relative rate of diffusion of Helium to Neon?
Ans) 2.24
Interpretation: Helium particles will diffuse times faster than Neon particles

14. Additional Examples
3. Compute the relative rate of diffusion of argon to radon
4. Compute the relative rate of diffusion of helium to argon
Ans 3) 2.36
Ans 4) 3.16

15. Practice
A sealed can with an internal pressure of 721 Torr at 25 ˚C is thrown into an incinerator operating at 755˚C. What will be the pressure inside the heated can, assuming that container remains intact during incineration?

16. Practice
How many molecules are in a gas that has a pressure of 6 kPa, a volume of 5 L, and a temperature of 127°C?
Ans) moles or 5.44 x 1021 molecules

17. Practice
What is the volume of 1.00 mole of a gas at stadard temperature and pressure?

18. Practice
A 113 L sample of helium at 27˚C is cooled at constant to -78.0˚C. Calculate the new volume of the helium.

19. Practice
What volume of He is occupied by 2.35 mol of He at 25˚C and a pressure of atm?