Announcements
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Exam #1: Tuesday, September 25th,
7:00-8:15pm, locations on website
Conflict Exam: 5:15-6:30pm, 114
Transportation Bldg, sign up outside of
101 CA until noon on 9/25
Review Questions for Exam 1 due
tomorrow by 5:00pm
Q & A Review Sessions
TAs
Sections
Zack Gordon
BDB, BDC, BDE,
Doug Rybar
BDJ, BDK, BDM
Nitin Neelakantan
Liz Ohr
BDD, BDF
Anna Wetherholt
Alex Stanton
BDA, BDG, BDI
Puzhou Wang
Lauren Cunningham
BDH
Derek Le
BDL
Time and Location
Sept. 23 (Sun) 1-3 pm
217 Noyes Lab
Sept. 23 (Sun) 4-6 pm
161 Noyes Lab
Sept. 20 ( Thurs) 7-9 pm
1002 Lincoln Hall
Sept. 23 (Sun) 7-9 pm
165 Noyes Lab
Sept. 20 (Thurs) 5-7 pm
162 Noyes Lab
Demo: motion of gas
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Can filled with balls – model of gas in
container
Pressure (P): can “hear” pressure (collisions
with sides of can)
Volume (V): size of can
Moles (n): number of balls (amount of gas)
Temperature (T): how fast you shake can
Demo: motion of gas
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How would you increase the pressure?
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Increase moles (more balls)
Decrease volume (smaller can)
Increase temperature (shake faster)
Gets us to idea of WHY we observe
these relationships between P, V, n
and T
Pressure: Microscopic
Why do we observe pressure?
 Collisions of gas particles with walls of
container
 To increase pressure:
 increase number of collisions (faster
particles)
 increase force of the collisions
(heavier particles)
Partial Pressures
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Pressure is additive
P(total) = P1 + P2 +P3….
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Example: container with N2 and H2
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same volume for P(N2) and P(H2)
same temperature for P(N2) and P(H2)
Important when doing problems involving
partial pressure
Temperature and energy
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Temperature is measure of average
kinetic energy of a sample
Related to average velocity of gas
particles and mass
KE = ½ mv2
Energy of movement, how fast
particles are moving
Temperature and motion
DEMO: Hot versus cold
 Drop food coloring into beaker of cold
water and beaker of hot water
 Which spreads faster?
 Food coloring spreads faster in hot
beaker because molecules are moving
and colliding faster than molecules in
cold beaker
Kinetic Molecular Theory
Gases are made of particles in
constant random motion.
 Temperature is a measure of
random kinetic energy.
 Pressure is due to collisions of
gas particles with container.
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KMT (assumptions)
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Assume that gas particles exert no
attractive forces (elastic collisions).
Assume volume of gas particles is
negligible (zero).
KMT (Assumptions)
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Assumptions are more likely to be true if:
 High temperature (very hot)
 Large volume (to move around in)
 Low pressure
This will cause gas molecules to hit less
often (which gets around “attractive” forces)
But let’s talk about mass and pressure now
Clicker #1
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The two balloons above are the same size but contain different
gases. How do the pressures inside the balloons compare?
A)
B)
C)
D)
The pressures are the same.
The balloon with helium (He) has the greater pressure.
The balloon with xenon (Xe) has the greater pressure.
Not enough information is given to answer this question.
Clicker #2
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The two balloons above are the same size but contain different
gases. Which gas particles will hit the walls of the balloon harder?
A)
B)
C)
They both hit with the same amount of force.
The helium particles will hit harder.
The xenon particles will hit harder.
Mass and pressure
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Why does Xe hit the wall harder?
 because it has a larger mass
Why does He have the same pressure then?
 Because He moves faster and makes up
for the mass difference
Heavier gas particles move slower
Lighter gas particles diffuse faster
Clicker #3
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You are holding three balloons each containing
the same mass of gas. One balloon contains
hydrogen gas, one contains helium, and one
contains oxygen. Which balloon is the largest?
A)
B)
C)
D)
The hydrogen balloon is the largest.
The helium balloon is the largest.
The oxygen balloon is the largest.
All of the balloons are the same size.
Example
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You are holding three balloons each containing
the same mass of gas. One balloon contains
hydrogen gas, one contains helium, and one
contains oxygen. Draw the relative sizes of
these balloons. (Assume P and T are constant)
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A 50.0-L steel tank contains 186
mol N2 and 145 mol O2 at 24oC.
What is the partial pressure of each
gas in the tank? What is the total
pressure in the tank?
Consider a sample of gas at 2.00
atm in a 35.0-L container at 25.0oC.
You transfer all of the gas to a
70.0-L container and you heat the
gas to 50.0oC.
Determine the new pressure of the
gas.
Consider a sample of gas at
5.40 atm in a 1.00-L rigid
container at 40.0oC. You heat
the gas to 80.0oC. What
happens?
Solve for the new condition.
Consider a sample of gas at
5.40 atm in a 1.00-L container
fitted with a piston at 40.0oC.
You heat the gas to 80.0oC.
What happens?
Solve for the new condition.