Transcript Gas Laws - University of California, Irvine

Kinetic Molecular Theory and Real
Gases
ROOT MEAN SQUARED, EFFUSION, REAL GASES
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ANNOUNCEMENTS
Remember back 5
rows of even side
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• I still don’t have midterm 3 back, it’ll be up as soon as I have them.
• Figure out grade using midterms and assume as long as you show up most classes and do most of the homework it’ll
balance out. (you get to drop enough that generally it shifts the curve up for everyone)
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as things you don’t like so I don’t change things most people like due to the vocal few.
• Homework for chapter 11 are shorter assignments, there are just three of them because of how the chapter breaks
up.
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SURVEY QUESTIONS
• Mass Issues:
• Why do you convert into kg for the equations in this section?
• R is in
𝐽
𝑚𝑜𝑙∗𝐾
and J has a Kg unit in it so it needs to cancel.
• Why was the kg/mol in the example for He 4.003x10-3kg?
• On periodic table it is 4.00 g/mol, divide by 1000 to convert into
kg/mol.
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SURVEY QUESTIONS: TEMPERATURE ISSUES
• For the RMSspeed equation, do we always
use 298K when we are not given a
temperature value?
Why does temperature make volume bigger?
• You should always be given it or a way to
calculate it. Otherwise ask.
• STP is 0oC, aka 273 K
• If given two temp in oC and asked for final
volume do we need to convert celsius to
kelvin
• Yes, always always always always convert into
Kelvin when dealing with temperatures in this
unit.
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Low temp,= slower moving
Either, less pressure, or less
volume
High temp= faster moving
Either, higher pressure, or
higher volume
Pressure changes if rigid container
Volume changes if non rigid
container/movable piston ect…..
QUIZ QUESTION 1
• Which is true according to the kinetic molecular theory?
• Molecules are point masses
• Collisions are elastic
• Gas molecules are attracted to each other
• Gas molecules repel each other
• Gas molecules are neither attracted nor repulsed
• Gas molecules in a sample are all traveling at the same speed
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KINETIC MOLECULAR THEORY OF GAS
• What is Kinetic energy?
• Energy of motion
• Kinetic theory of gases
• Assume molecules are point masses (possess mass but no volume)
• Constant random motion, collisions are completely elastic
• energy can be transferred, but total energy remains the same.
• Gas molecules are neither attracted or repulsed
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KINETIC MOLECULAR THEORY: PRESSURE
• Pressure is created by collisions between molecules and the container.
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DISCUSSION QUESTIONS: KINETIC MOLECULAR THEORY
• Do all your molecules hit the walls of their container with the same force?
Justify your answer based on kinetic molecular theory.
No:
Not all molecules are traveling at the same speed,
since force increases as velocity increases, a molecule
traveling faster will hit with more force.
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• Which of the two lines represents the sample at a higher temperature?
Higher temp= faster rms
T2= faster rms= higher temperature
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• Which of the two lines represents with a higher molecular mass?
M1
Smaller mass = faster rms
M2
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M1= slower rms= heavier
DISCUSSION QUESTIONS: KINETIC MOLECULAR THEORY
• How does the frequency and force (respectively) of the collisions of the molecules
of a gas with the walls of the container change as the temperature of the gas is
decreased? Justify based on kinetic model of gases.
Decrease, Decrease
The distribution of speeds is lowered as the temperature is lowered, so
the molecules will hit the walls less often due to slower movement, and
will also hit with less force due to slower movement.
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DISCUSSION QUESTIONS KINETIC MOLECULAR
THEORY
• If you increase the molecular mass, the rms ____________. Justify your answer
• A) Increases
B) Decreases
C) stays the same
Decreases
The rms speed is as shown in the formula below. Therefore it is inversely related to
molecular mass. The more mass a molecule has, the slower it will go.
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• Calculate the rms speed of an oxygen gas molecule, O2, at 29.0∘C .
3𝑅𝑇
𝑢𝑟𝑚𝑠 =
𝑀
𝑢𝑟𝑚𝑠 =
𝐽
3 8.314
𝐾 ∗ 𝑚𝑜𝑙
29.0 + 273.15 𝐾
𝑘𝑔
0.032000
𝑚𝑜𝑙
=
485 𝑚 𝑠
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• Explain how each of the below laws follow from kinetic molecular theory. LearningCatalytics: session ID: 95960120
• Boyle's law, (P&V):
P1V1=P2V2
If the pressure is decreased, the force on the walls must be decreased. This happens by decreasing the
frequency of collisions by increasing the size of the container.
• Charles's law(V&T)/Gay-Lussac’s(P , T),
P1/T1=P2/T2
If the temperature is increased the force on the walls will increase as well. This is from both increased
number and increased speed of collision. This increases the pressure.
• Avogadro's law, (n&V or P)
V1/n1=V2/n2
If the number of moles is increased the number of collisions with the wall will increase, therefore increasing
the volume.
• and Dalton's law (partial pressures)
Pa+Pb+Pc…..=Ptotal and that PV=(na+nb+nc…)RT
Because all the molecules will hit the wall with the same force (faster molecules are lighter at the same
temperature),