What a Gas!
OBJECTIVES
1. Students will be able to describe three postulates of the kinetic molecular theory from experimental data and
observations.
2. Students will explain the relationship between gaseous temperature, pressure, and volume based on
experimental data and observations.
PROCEDURE
* For each activity, read it completely before starting DO NOT WRITE IT DOWN.
Activity I: Background on Gases
Directions: Read through the handout (page 7 of this lab). Answer the following questions. You may need
to refer to the reading when answering questions in other activities.
Activity I: Questions:
1. List some basic properties of gases.
2. What causes gas pressure? b. Gas pressure is measured in what unit?
3. What is temperature of a gas? b. Gas temperature is measured in what unit?
4. What is kinetic energy?
5. Using the definition of kinetic energy, explain what the definition of temperature.
-----------------------------------------------------------------------------------------------------------------Activity II: Investigating the Motion of Gas Particles. (Adapted from Guzdziol, n.d.)
WARNING: Do not heat the cage for a long time, it will become very HOT.
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Read the directions and make a data/observations chart in your notebook.
Place 5 small gas particles (Styrofoam balls) into the small cage.
Hold the hairdryer about 6 inches from the opening at slight angle.
Make observations when the hairdryer is on LOW speed and HIGH speed. Record.
Place 5 Styrofoam balls in the large cage.
Make observations when the hairdryer is on LOW speed and HIGH speed Record.
Data/Observations: Record in your notebook.
Activity II Questions:
A. In this model, what do the Styrofoam balls and hamster cage represent?
B. When the hairdryer is changed from LOW speed to HIGH speed, this represents a temperature change.
What is the happening to the temperature of the gas when the hairdryer goes from LOW speed to HIGH
speed?
C. As the heat increases what happens to the number of collisions between the particles and the wall of the
container?
Target Inquiry GVSU-2007, Alice Putti, Jenison High School
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D. What happens to the gas pressure?
E. Write a rule for what happens to the pressure of a gas as the temperature is increased (given the same
volume).
F. When moving to the larger cage what have we changed about the container?
G. Describe how the collision of the gas particles in the large cage compares to the collision in the small
cage?
H. As a result what has happened to the gas pressure inside of the container?
I. Write a rule (algebraic) for the relationship between volume and pressure (given the same temperature).
Activity III: Effect of Temperature on the Volume of a Gas.
Read through the directions and then make a data table and graph.
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Place the beaker in overflow-catching trays.
Fill the beakers with tap ice water and hot water. Fill them completely full.
Measure the temperature of the water. Record.
Slowly submerge the balloon in the hot water so that the tie is just above the water level but not so deep
that the water covers the entire balloon. Hold the balloon in the water to allow the balloon and its
contents to reach the temperature of the water.
5. Measure the amount of overflow using a graduated cylinder. Record.
6. Repeat using the same balloon but very slowly submerge it in the ice water. Record water temperature
and overflow.
Data Table and graph: create in lab notebook
Activity III Questions:
A. What happened to the size of the balloon when it was placed in the hot water?
B. What happened size of the balloon when it was placed in the cold water?
C. The term for the amount of space that the gas in the balloon occupies is known as _____?
D. Why is it necessary to precool the balloon before you put it in the beaker to overflow?
E. Write a rule (algebraic) for the relationship between the answer to “C” and the temperature of the gas.
Target Inquiry GVSU-2007, Alice Putti, Jenison High School
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Activity IV: Attractive Forces Between Molecules
Using a graduated cylinder and small rubber stopper (if at home a tall glass and a coin works) answer/do the
following.
1. Look at the 100 ml graduated cylinder. At this time what is inside it?
2. Drop a rubber stopper into the graduated cylinder. Observe how long it takes to reach the bottom.
3. Now fill the graduated cylinder with water. Drop the rubber stopper into the graduated cylinder. How
long does it take to reach the bottom?
Activity IV: Questions:
A. One factor that determines the state of matter is the attractive forces between the particles. The stronger
the attractive forces the closer the particles are to each other. Based on this activity how do the attractive
forces in a liquid compare to those in a gas?
B. How do you know that there is a difference between the attractive forces?
C. Write a statement that compares the attractive forces between a liquid and gas?
-----------------------------------------------------------------------------------------------------------------Activity V: Computer-Modeling the Motion of Gas Particles
1. Go to the following website: http://phet.colorado.edu/en/simulation/gas-properties
2. Add 100 heavy species particles
What are the temperature, pressure, and volume of the particles? T= P= V=
3. Do your best to watch one particle for a while.
Are all the particles moving at the same speed as the one you watched?
4. Does the particle you watched always move at the same speed?
In other words does it ever speed up or slow down?
When does it change speed?
5. Observe the particle again.
a. Describe the motion of the particle. (straight lines? curves? squiggly? corkscrew patterns?)
b. When does the particle change direction?
6. a. If the volume was decreased to ½ the original volume, PREDICT what you expect would happen to the
number of collisions? And therefore what will happen to the pressure?
b. What do you think will happen to the average kinetic energy of the particles and therefore the temperature?
7. Change the Volume to about ½ the original volume and observe.
8. Did the temperature change? Record it.
9. What does the result from #8 tell you about the average kinetic energy of the gas particles?
Target Inquiry GVSU-2007, Alice Putti, Jenison High School
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10. Observe the collisions that are occurring between the particles and the walls of the container. How do the
collisions now compare to before the volume was adjusted? Does anything unexpected happen?
11. What is the pressure?
12. Were your predictions correct? Explain.
13. Reset the program and add 100 heavy species particles again.
14. a. If the temperature was increased by 200 K, PREDICT what should happen to the number of collisions
between gas particles?
b. What should happen to the gas pressure?
15. Add heat to change the temperature up about 200K more.
Observe the number of collisions that are occurring now. How do the particle’s collisions now compare
to those before the temperature was changed?
16. Were your predictions correct? Explain.
17. If you add heat for as long as possible. What do you think will happen to the temperature and pressure?
18. Add heat and keep adding. What happens?
GOING FURTHERQUESTIONS
1. The warning on an aerosol hairspray can states: Do not store at a temperature above 120°F (50 °C).
What happens if the hairspray is heated above this temperature?
b. In terms of the particles, describe how this occurs if the hairspray is heated above 120 F?
2. If a student brings hot French fries into the classroom, eventually everyone in the room can smell them.
Explain how/why this happens?
3. In the reading, it stated that the atmospheric pressure was lower at high elevations. Why is this? (Hint:
Think about what holds that atmosphere around the Earth).
4. In the reading, it is explained that good weather is associated with high atmospheric pressure. In terms
of the air particles what does high atmospheric pressure mean?
5. The reading states that air particles travel from high atmospheric pressure to low. What does this
statement mean?
Target Inquiry GVSU-2007, Alice Putti, Jenison High School
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Property of Gases
Gases are easily compressible and expandable due to the amount of space between the particles. In addition gas
particles constantly move randomly in straight lines until they collide with other gas particles or the wall of the
container (See Figure 1). As a result gases will fill their containers regardless of size or shape. Gas pressure is a
measure of the collisions of gas particles with the walls of a container. Atmospheric pressure is the collision of
air molecules with the Earth’s surface. The pressure of a gas can be measured in pounds per square inch (Psi),
atmospheres (atm) or the metric unit of Pascal (Pa) as well as other units such as mmHg. The instrument used to
measure gas pressure is the barometer.
The pressure of a gas is influenced by the volume of the container and the temperature of the gas. The
temperature of a substance is the average kinetic energy of the particles. Gas temperature is measured in
degrees Kelvins and is proportional to the average kinetic energy of the particles.
Gases in Your Everyday Life
Gases have a large impact on your life. As mentioned above, atmospheric pressure is the collision of air
molecules with the surface of the Earth. This pressure is used to predict the weather. In general high
atmospheric pressure means good weather and low pressure means stormy weather. In high pressure areas the
air density is greater than the surrounding areas. Air molecules like other gases always move from high to low
pressure, resulting in blowing air or wind that flows from a high pressure area to low pressure area. When the
wind blows into the low pressure area, it causes the air to rise and form precipitation and clouds which can form
thunderstorms.
Another example of how gases affect your life occurs when you fly on a plane. When flying in an airplane, you
may have noticed that your ears “pop” when you take off and land. This is due to a change in air pressure at
different altitude, the higher the altitude the lower the air pressure. Your ears “pop” when the air pressure
inside your ear changes to match the outside air pressure.
Figure 1. Gas particles travel
far, relative to their size, in
straight lines until they collide
with another molecule or side of
the container.
Target Inquiry GVSU-2007, Alice Putti, Jenison High School
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