SAM Teachers Guide Gas Laws Overview Students explore how volume, pressure, temperature and density of gas molecules interrelate. They cover Boyleʹs, Charlesʹs, Gay‑Lussacʹs and Avogadroʹs laws. Students are then are asked to solve a challenge. Learning Objectives Students will be able to: • Describe gas pressure as it relates to collisions of molecules on a surface of an object. • Explore the relationship between pressure, volume, temperature, and number of particles as shown in the Ideal Gas Law (PV = nRT). • Describe the relationship between pressure and volume in a gas. (Boyle’s law) • Describe the effect of varying the temperature on the volume of a gas. (Charles’s law) • Describe the relationship between temperature and pressure in a gas. (Gay‑
Lussac’s law) • Explain the relationship between the number of particles and volume of a gas as demonstrated by Avogadro’s law. • Create a model demonstrating why the soda can collapsed and explain the model using the gas laws. Possible Student Pre/Misconceptions • Gases have no mass. • Gases move in a set path. • Gases are invisible and cannot be contained. Therefore, they cannot exert pressure. Models to Highlight and Possible Discussion Questions After completion of the activity: Models to Highlight: • Page 2 – Balloon Cross Section o Highlight what happens as atoms are added to and removed from inside the balloon and use this as a way to review student understanding of gas pressure. • Page 3 – Pressure / Volume Relationship Model •
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o Highlight that when temperature is kept constant, pressure and volume exhibit a clear relationship. As volume increases, pressure decreases. As volume decreases, pressure increases. Page 4 – Temperature / Volume Relationship Model o Highlight that when pressure is kept constant, as temperature increases, volume increases. As temperature decreases, volume decreases. They are directly proportional. o Link to other SAM activities: Heat and Temperature. Discuss how change in temperature affects the motion of atoms. Page 5 – Temperature / Pressure Relationship Model o Highlight that when volume is kept constant, as temperature increases, pressure increases. As temperature decreases, pressure does so as well. Page 6 – Number of Particles / Volume Relationship Model o Highlight that temperature and pressure were kept constant in this model. When this is the case, increasing the number of particles is directly related to increasing the volume. Page 7 – Soda Can Demonstration Model o Have students share the models they created and the challenges they faced while creating the models. Did it work on the first try? Or were they able to determine the relationship at work by using the model itself? Possible Discussion Questions: • Demonstration/Laboratory Ideas: Have students watch the Soda Can Demonstration and / or the Liquid Nitrogen Plus Balloon Demonstration in the lab. This will evoke class discussion and give students a firsthand account of what happened. • What is temperature? [Link back to the previous SAM activity: Heat and Temperature.] • How does the model of the balloon on page 2 relate to Newton’s third law? [Link back to previous SAM activity: Newton’s Laws at the Atomic Scale.] • If scientists wanted to know the relationship between all of the factors in the gas law (pressure, volume, temperature, number of particles), why do they set one (or more) as constants to study these relationships? How does this relate to the scientific method? • Brainstorm other phenomena that exist in the world around us and explain them in terms of the gas laws. Connections to Other SAM Activities This activity focuses on the relationships between pressure, volume, temperature, and number of particles in a gas. This activity is supported by the Heat and Temperature activity, which illustrates how a change in temperature is related to an increase in kinetic energy. Students learn that it is the increased collisions of particles with that container that builds pressure. Newton’s Laws at the Atomic Scale illustrates how particles move in a straight line until they encounter collisions. Finally, Phase Change introduces the molecular arrangement of atoms in different states. This activity supports Diffusion, Osmosis, and Active Transport. Here, dissolved substances behave in a manner that is very similar to that of gas particles. They spread out to fill their container. In addition, osmotic pressure is very similar to pressure created by gas molecules as they collide into the walls of their surroundings. Activity Answer Guide Page 1:
Introduction, no questions
Page 2:
1. Remove atoms inside the balloon until
there are fewer than 20 atoms. Run the
model for a minute, take a snapshot, and
drag the image into the box below. 3. How does adding and removing atoms
affect the position of the balloon's skin (the
rectangle)?
When atoms are removed, the balloon's skin
moves to the left or starts to be pushed inward.
There are more gas particles outside the balloon
exerting pressure than inside. When atoms are
added to the balloon, the balloon's skin moves to
the right. The increased pressure inside the
balloon causes the skin to expand.
4. Can you think of other ways of increasing
the number of collisions on the inner surface
of the balloon without adding more atoms to
it?
Increasing the temperature or the speed of
atoms moving inside the balloon will increase
the number of collisions the atoms will have with
balloon.
This image shows the model when there are
only 16 atoms inside the balloon. It had a
chance to run for about a minute after the atoms
were removed.
2. Add atoms inside the balloon until there
are more than 60 atoms. Run the model for a
minute, take a snapshot, and drag the image
into the box below. Page 3:
Point 1
Volume: 3
Pressure: 0.33
Point 2
Volume: 4
Pressure: 0.23
Point 3
Volume: 5
Pressure: 0.16
Point 4
Volume: 2
Pressure: 0.52
This image was taken after there were 65 atoms
inside the balloon and the model was allowed to
run for about a minute.
9. According to your data, which of the four
graphs above best represents the
relationship between pressure and volume of
a gas at constant temperature?
(a)
10. Which of the following best describes
what occurred as the volume increased?
(b)
11. In your own words, describe the
relationship between pressure and volume.
Making the container smaller (decreasing the
volume) causes the pressure exerted by the gas
molecules to increase. Making the container
larger (increasing the volume) makes the
pressure decrease. Conclusion: As volume
increases, pressure decreases and vice versa.
Page 4:
1. Why does the piston move when the
temperature changes? Include in your
answer how molecules colliding with the
piston can account for the movement of the
piston.
As temperature increases, the molecules are
moving faster and colliding more frequently with
a greater force, thus moving the piston to the
right and increasing the volume. The opposite is
true as temperature is decreased.
2. Use the slider to select a lower
temperature, run the model for a minute, take
a snapshot and describe what happens to
the volume of the gas.
This image was taken when temperature was
raised. Here, you can see that the volume has
increased.
4. In your own words, describe the
relationship between temperature and
volume in the ideal gas law. As temperature increases the volume increases.
As temperature decreases so does the volume.
Page 5:
1. Which of the following best describes
what occurred as the temperature
increased?
(a)
2. How does changing the temperature of the
gas affect the pressure?
Decreasing the temperature of the gas
decreases the pressure exerted by the gas
molecules. Increasing the temperature of the
gas increases the pressure exerted as the gas
molecules are in more rapid motion with more
numerous collisions.
3. In your own words, describe the
relationship between pressure and
temperature.
Temperature and pressure are directly
proportional. As temperature increases in a
closed system, so does pressure. As pressure
increases, so does temperature.
This image was taken when the temperature
was lowered. When the temperature is lowered,
the volume also decreases.
3. Use the slider to select a higher
temperature, run the model for a minute, take
a snapshot, and describe what happens to
the volume of the gas .
Page 6:
Volume Measurements Taken from Model:
1. 120 molecules - 31
2. 100 molecules - 28
3. 80 molecules - 22
4. 60 molecules - 16.8
5. 40 molecules - 11
6. 20 molecules - 6
7. Which of the four graphs below best
represents the relationship between the
number of particles and volume of a gas (at
constant pressure and temperature)? (d)
8. Which of the following best explains what
occurred as the number of particles
decreased (check all that apply)?
(d)
9. In your own words, describe the
relationship between volume and number of
molecules.
The relationship between volume and number of
molecules is directly proportional. As the number
of particles increases, so does the volume or the
space that these particles occupy.
Page 7:
1. Take a snapshot that illustrates that you
figured out the reason why the soda can
collapsed.
of the gas decreases the pressure until the can
implodes.
Page 8:
1. Which relationship of the following best
explains this experiment?
(b)
2. Explain why the balloon shrank and then
expanded in this experiment.
As the temperature of the balloon decreased
drastically in the presence of liquid nitrogen, the
balloon deflated. That is, its volume decreased
as well. As the liquid nitrogen evaporates, the
temperature begins to rise and the gas
molecules expand again to re-inflate the balloon.
As we learned through the page 4 model, as
temperature increases, volume does as well.
3. List two ways you can increase the
pressure in a container with a fixed volume
and explain why this causes a pressure
increase.
An increase in the number of particles in the
container or the temperature of the particles in
the container would both lead to an increase in
pressure. In both cases, the molecules
encounter more collisions.
The particles inside the soda can get colder as it
is plunged into the ice water. As temperature
decreases, so does the pressure inside the can
compared to the pressure outside the can.
2. Use your understanding to explain why the
coke can on the first page collapsed.
Assume the can was sealed when it was
placed in the ice water.
The water inside the can is first heated on the
hot plate to create steam. The steam is then
drastically cooled when the can is plunged into
the ice water. As the temperature decreases, the
steam condenses into liquid water. Pressure
outside the can is much higher than that inside
the can. The can collapses because of the
pressure difference. Decreasing the temperature
4. SCUBA tanks have to be built to withstand
very high pressure because many gas
molecules are put inside them. Why would
putting more molecules inside cause high
pressure?
Molecules of a gas are in constant, random
motion. When more molecules are present
inside a fixed volume (such as a SCUBA tank),
there are more opportunities for collisions
between molecules, which leads to an increase
in pressure inside the tank.
SAM HOMEWORK QUESTIONS
Gas Laws
Directions: After completing the unit, answer the following questions to review.
1. The Ideal Gas Law states that PV = nRT. Identify each of the variables in the equation
in the space below.
P: _____________V: _____________ n: ______________ R: ___________ T: ______________
2. What is the relationship between pressure and volume in a gas?
3. When pressure is kept constant, what is the relationship between temperature and volume
in a gas?
4. What is the relationship between temperature and pressure in a gas?
5.
BEFORE – Volume Reading = 6.0
AFTER- – Volume Reading = 32.0
Look at the BEFORE and AFTER pictures above. What is the effect of adding atoms on the
volume of a gas? Why does this happen?
6. Career connection: On April 20, 2010 the largest marine oil spill in the history of oil
drilling occurred when there was an explosion on the Deepwater Horizon drilling
platform. A large part of what was released from the well was methane gas. To create
some method for capping the well, computer models were used of gas pressure and
behavior under various temperatures and pressures. Find some other recent use of
modeling gases.
SAM HOMEWORK QUESTIONS
Gas Laws – With Suggested Answers for Teachers
Directions: After completing the unit, answer the following questions to review.
1. The Ideal Gas Law states that PV = nRT. Identify each of the variables in the equation
in the space below.
P: pressure
V: volume
n: number of particles
R: constant
T: temperature
2. What is the relationship between pressure and volume in a gas?
As explained by Boyle’s Law, pressure and volume are inversely proportional. As volume increases, pressure
decreases. As volume decreases, pressure increases.
3. When pressure is kept constant, what is the relationship between temperature and volume
in a gas?
As explained by Charles’ Law, temperature and volume are proportional in a closed system. Therefore, as
temperature increase, volume also increases. As temperature decreases, volume decreases.
4. What is the relationship between temperature and pressure in a gas?
As explained by Gay-Lussac’s Law, temperature and pressure are proportional in a closed system. When
temperature increases, pressure increases. When temperature decreases, pressure decreases.
5.
BEFORE – Volume Reading = 6.0
AFTER – Volume Reading = 32.0
Look at the BEFORE and AFTER pictures above. What is the effect of adding atoms on the
volume of a gas? Why does this happen?
As the number of particles increases, so does the volume. Number of particles and volume are proportional in a
closed system according to Avogadro’s Law. Adding more particles causes more collisions between particles and
the need for particles to spread out to maintain a constant pressure.
6.
Career connection: Use an internet search to find lots of examples. Modeling of gases is
done for geological engineering, production of fuel through anaerobic digestion, design
of shock absorbers for cars, etc.