SLIDE 1
Sparks CH301 DIFFUSION AND EFFUSION MIXTURES – Day 6 HW Posted
SLIDE 2 What did we learn last time?
Ideal Gas is amazing – empirically derived and also theoretically derived. We now know how to relate rms velocity to both temperature and mass Finally, there is a distribution of velocities. This will have huge implications for future understanding of chemistry!
SLIDE 3 Demo
Let’s think about our demo. What is the ratio
- f the speeds of the two molecules in our
demo? NH3 : HCl
Numerical Question: Give an answer to one decimal place
SLIDE 4 Standard Molar Volume
One mole of any ideal gas occupies 22.4 L at STP
Most real gases have standard molar volumes within 2% of this value.
SLIDE 5 Try it Out! Avogadro Example 1 What is the density of CO2 gas at STP?
- A. 1.96 g/L
- B. 44 g/L
- C. 0.05 g/L
- D. 1050 g/L
SLIDE 6 Engaging in practice matters…
Illusion of Understanding
- Watching isn’t the same as doing
Maximize Learning Opportunities
- test your understanding
- make mistakes
- receive coaching
SLIDE 7 What are we going to learn today?
EFFECT OF VELOCITY ON DIFFUSION AND EFFUSION REPRESENTING GAS MIXTURES Concept of Partial Pressures
SLIDE 8 Diffusion and Effusion
Diffusion: Spread of particles due to random motion (perfume “smell” wander across the room) Effusion: Loss of gas from a container through a small pore. (He balloon that deflates slowly) Both directly related to the velocity of the gas particles
SLIDE 9
Effusion
SLIDE 10 You have two gases under identical conditions. One gas has a density that is double that of the
- ther gas. What is the ratio of the rate of diffusion
- f the high density gas compared lower density gas
POLL: CLICKER QUESTION
- A. 2 times less
- B. Sqrt(2) times less
- C. 2 times faster
- D. sqrt(2) times faster
- E. they are identical
SLIDE 11 Figure 5.20: Uranium-enrichment converters from the Paducah gaseous diffusion plant in Kentucky.
Actually- this is technically effusion...!
SLIDE 12
SLIDE 13 MASS DENSITY FOR GASES
THINK BACK TO BALLOONS SAME T & P DIFFERENT DENSITIES WERE DUE TO THE DIFFERENT MASSES OF THE GAS “PARTICLES” WHAT ABOUT MIXTURES?
SLIDE 14 How to describe a mixture
Two containers of equal volume separated by a wall
nHe= mole He T = 300K P = 1 bar nAr = mole Ar T = 300K P = 1 bar
SLIDE 15 Mixtures
Remove the wall. What is the total pressure?
Groupwork quiz
SLIDE 16
Partial Pressure
Total pressure is still 1 bar
Where does the pressure come from? We can think of dividing it up into the pressure from the He and the pressure from the Ar.
SLIDE 17 Mixtures
Half the particles are Ar so half the pressure should be from Ar
SLIDE 18 Mixtures
The same is true for He
PHe = nHeRT/V nHe is half the number of total moles So PHe is half the total pressure
SLIDE 19
Partial Pressure
This is what we call “partial pressure”
In a mixture, the partial pressure of gas “i”
Pi = niRT/V
SLIDE 20
Dalton’s Law
The sum of all partial pressure must be the total pressure
SLIDE 21
Mole Fraction Percentage
What fraction of the particles are gas “i”?
SLIDE 22
Mole Fraction Percentage
What fraction of the particles are gas “i”?
Mole fraction Xi is the number of moles i divided by the total number of moles
SLIDE 23
Mole Fraction Percentage
What fraction of the particles are gas “i”?
Mole fraction Xi is the number of moles i divided by the total number of moles
SLIDE 24
Mole Fraction Percentage
What fraction of the particles are gas “i”?
Mole fraction Xi is the number of moles i divided by the total number of moles
SLIDE 25
Mole Fraction Percentage
What fraction of the particles are gas “i”?
Mole fraction Xi is the number of moles i divided by the total number of moles
SLIDE 26
Mole Fraction Percentage
What fraction of the particles are gas “i”?
Mole fraction Xi is the number of moles i divided by the total number of moles
SLIDE 27 Two tanks are connected by a closed valve. Tank A, filled with O2, has a volume of 2 L and a pressure of 5 atm. Tank B, filled with N2, has a volume of 4 L and a pressure of 10 atm. The valve is opened. What is
- 1. The partial pressure exerted by oxygen?
- 2. The total pressure exerted by the mixture?
- 3. What is the mole fraction of nitrogen?
Report each answer to one decimal place
SLIDE 28 What did we learn today?
We can apply our knowledge of velocities to diffusion and effusion of gases We can utilize the idea of partial pressures and mole fractions to understand more about a gas sample.
SLIDE 29 DAY 6 LEARNING OUTCOMES
Perform calculations to determine the mole fractions of gases within and gas mixture and relate mole fraction to the partial pressure of a gas within a gas mixture. Describe the relationship between partial pressures and the total pressure as described in Dalton’s Law of Partial Pressure.
