Transcript Real Gas example (we may not have time for this one the

Effusion and Real Gases
• Announcements:
• Tutor Review Session from 5-7 tonight in DBH 1100
Remember back 5
rows of even side
are no seating zones
• Added additional gas law questions to “sample exam” questions. Posted on website
• Studying for the final
• video questions (level 1), in class worksheets (level 1-3), mastering homework (level 1-5), sample midterm
questions(level 1-5), sample final questions(level 1-5)
• Office hours next week. (see calendar)
• Mine RH 214: Monday 10-11:30, Monday 2-3:00, Tuesday 3-4
• Pauls 3rd floor NSI : Tuesday 12-1
• Survey question comment: if you are still having problems with geometry, hybridization, chapter 5, 8 ect….
Please please come see me in office hours, we don’t have enough class time to go back and do this but Paul
and I can help you in office hours!
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SURVEY QUESTIONS.
• Choosing R:
• Things involving energy, 8.314
𝐽
𝐾 𝑚𝑜𝑙
or Things involving volume and pressure
𝐿∗𝑎𝑡𝑚
0.0821
𝑚𝑜𝑙 𝐾
• Don’t bother with the other 15 or so versions, just stick with these two and convert other units
to match.
• How do you know which number to plug in for R1 and R2, and M1 and M2 (and
my addition to this: what about T1 and T2?)
• Make sure they match and it doesn’t matter! If it helps you can label them a/b instead of
1/2
• Light molecule= fast rate= short time
• Heavy molecule= slow rate= long time
• Ratio a to b of 1.2: a=1.2, b=1
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SURVEY QUESTIONS.
• Do we get gas conversions on the exam? Do we get a and b for the Van der
Waals equation on the exam?
• Of course, you know I wouldn’t make you memorize such things.
• Whats your favorite color on the electromagnetic spectrum.
• Around 510-515nm ish.
• Survey question comment: if you are still having problems with geometry, hybridization, chapter
5, 8 ect…. Please please come see me in office hours, we don’t have enough class time to go
back and do this but Paul and I can help you in office hours!
Visit: https://checkin.ics.uci.edu/
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Review: Kinetic Molecular Theory of Gases
Which of the following is true?
•
The average speed of gas molecules decreases with decreasing temperature.
•
The kinetic energy of a molecule cannot determine its speed.
•
There are gas molecules that move slower than the average.
•
All the gas molecules in a sample cannot have the same kinetic energy.
•
The average kinetic energy of gas molecules decreases with decreasing temperature.
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Effusion: Process of escaping through tiny holes, (often into an empty container, although not always).
Diffusion: Movement of molecules (typically in liquid or gas) from area of high to low concentration through larger
openings.
A)
For each circumstance say if the gas is effusing, diffusing or neither:
Picture A)
Diffusion
Picture B)
Effusion
Movement of helium particles through a balloon causing it to deflate over time.
Effusion
Movement of helium particles into the air when the mouth of a balloon is opened.
B)
Diffusion
Enriching isotopes by using the difference in rms speeds to separate different mass molecules.
Effusion
Perfume molecules spread from
a spay on one side of the room to the other.
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Diffusion
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For an Oxygen and Bromine gas mixture which molecules have
the larger:
• Mass?
Bromine
• Greatest average velocity?
Oxygen
• Rate of effusion?
Oxygen
• Partial Pressure?
Same
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CONCEPT: KINETIC MOLECULAR THEORY EFFUSION:
• Without doing any calculations, put the following in order of increasing rate
of effusion and time of effusion. Molecular masses are in parenthesis.
• Ne (20.18 g/mol), C3H8 (44.11), He (4.00) and NO2 (46.01)
high mass equals slow (aka low rate, long time): low
mass equals fast (aka high rate, short time)
Rate:
NO2, C3H8, Ne, He
Time:
He , Ne, C3H8, NO2
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CALCULATIONS: KINETIC MOLECULAR THEORY
• What is the molar mass of a compound that takes 2.7 times as long to effuse through a
porous plug as it did for the same amount of XeF2 at the same temperature and pressure?
Hint:
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Talking about together
Real vs. Ideal Gas
• Under what types of pressure do gases behave ideally?
Low pressure
• Under what type of temperatures do gases behave ideally?
High temperatures
• We originally defined ideal gases with as series of requirements. These included, no volume, elastic collisions, and
they do not interact. Match these requirements with the conditions above.
No volume: Low pressure means volume of atoms are a lower percent of the total volume.
No interactions: High temperatures mean molecules are moving quickly and lots of
kinetic energy, interact less.
• We haven’t learned about how to tell if molecules interact with each other yet (it is in 1B), however, would a molecule
that strongly interacts with other molecules be more or less ideal?
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Less ideal.
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REAL GAS EXAMPLE
(we may not have time for this one the real
gas material, depending on the speed of
the class we may finish this up on Friday.)
a=4.562
b=0.0638
• Calculate the pressure exerted by 1.00 mol of C2H6 behaving as an
ideal gas and a Van der Waals gas when it is at 1) 273.15K in
22.414L and also 2) at 1000. K in 0.100L. Think about what these
answers tell you.
Conditions 1
Ideal Gas Law
Van Der Waals Gas
Rearranged for P
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REAL GAS EXAMPLE
(we may not have time for this one the real
gas material, depending on the speed of
the class we may finish this up on Friday.)
• Calculate the pressure exerted by 1.00 mol of C2H6 behaving as an
ideal gas and a Van der Waals gas when it is at 1) 273.15 in
22.414L and also 2) at 1000. K in 0.100L. Think about what these
answers tell you.
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Conditions 2
Ideal Gas Law
Van Der Waals Gas
Rearranged for P
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REAL GAS EXAMPLE
(we may not have time for this one the real
gas material, depending on the speed of
the class we may finish this up on Friday.)
• Calculate the pressure exerted by 1.00 mol of C2H6 behaving as an
ideal gas and a Van der Waals gas when it is at 1) 273.15 in
22.414L and also 2) at 1000. K in 0.100L. Think about what these
answers tell you.
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Summary
Condition 1
Atmospheric like
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Condition 2
High Pressure
Ideal Gas Law
Van Der Waals Gas
Difference
0.006atm
989atm
At atmospheric pressures gases act ideally. At high pressures they do not.
(Note: high temperatures in general actually make a gas act more ideally if still at a low pressure, however if
the high temperatures increase the pressure then the change in pressure causes gases to act non-ideally.)