In this activity you’ll use the Gas Properties PhET Simulation
(https://phet.colorado.edu/en/simulation/gas-properties) to explore and explain the relationships
between energy, pressure, volume, temperature, particle mass, number, and speed.
This activity has 5 modules:
○ Explore the Simulation
○ Kinetic Energy and Speed
○ Kinetic Molecular Theory of Gases
○ Relationships between Gas Variables
○ Pressure and Mixtures of Gases
You will get the most out of the activity if you do the exploration first! The rest of the sections
can be worked in any order; you could work on any sections where you want to deepen your
Part I: Explore the Simulation
Take about five minutes to explore the sim. Note at least two relationships that you observe and
Part II: Kinetic Energy and Speed
Sketch and compare the distributions for kinetic energy and speed at two different temperatures
in the table below. Record your temperatures (T1 and T2), set Volume as a Constant Parameter,
and use roughly the same number of particles for each experiment (aim for ~100-200). Use the
T2 temperature to examine a mixture of particles.
T1 = __________K The Species Information and Energy Histograms tools will help.
T2 = __________K The system is dynamic so the distributions will fluctuate.
Sketch the average or most common distribution that you see.
“Heavy” Particles Only “Light” Particles Only Heavy + Light Mixture
# of particles
sketch for T1
sketch for T1
sketch for T2
sketch for T2
1. Compare the kinetic energy distributions for the heavy vs. light particles at the same
temperature. Are these the same or different? What about the speed distributions?
2. Compare the kinetic energy distributions for the heavy vs. light particles at different
temperatures. Are these the same or different? What about the speed distributions?
3. Compare the kinetic energy distributions for the mixture to those of the heavy-only and light-
only gases at the same temperature. Are these the same or different? What about the speed
4. Summarize your observations about the relationships between molecular mass (heavy vs.
light), kinetic energy, particle speed, and temperature.
Part III: Kinetic Molecular Theory (KMT) of Gases
Our fundamental understanding of “ideal” gases makes the following 4 assumptions.
Describe how each of these assumptions is (or is not!) represented in the simulation.
Assumption of KMT Representation in Simulation
1. Gas particles are separated by
relatively large distances.
2. Gas molecules are constantly in
random motion and undergo
elastic collisions (like billiard
balls) with each other and the
walls of the container.
3. Gas molecules are not attracted
or repulsed by each other.
4. The average kinetic energy of
gas molecules in a sample is
proportional to temperature (in K).
Part IV: Relationships Between Gas Variables
Scientists in the late 1800’s noted relationships between many of the state variables related to
gases (pressure, volume, temperature), and the number of gas particles in the sample being
studied. They knew that it was easier to study relationships if they varied only two parameters at
a time and “fixed” (held constant) the others. Use the simulation to explore these relationships.
Variables Constant Parameters Relationship Proportionality
(see hint below)
pressure, volume directly proportional
volume, temperature directly proportional
volume, number of
Hint: A pair of variables is directly proportional when they vary in the same way (one increases
and the other also increases). A pair of variables is inversely proportional when they vary in
opposite ways (one increases and the other decreases). Label each of your relationships in the
table above as directly or inversely proportional.
Part V: Pressure and Mixtures of Gases
The atmosphere is composed of many gases in different ratios, and all of them contribute to the
total atmospheric pressure. Use the simulation to explore this relationship by testing
combinations of heavy and light gases.
For each Test #, record your measurement and the make the prediction before moving on to the
next row of the table.
(greater than, equal to, less than, twice as much, half as much, etc)
1 100 Light particles =
Pressure for 100 Heavy Particles will be __________________
the pressure from Test #1.
2 100 Heavy particles =
Pressure for 200 Heavy particles will be __________________
the pressure from Test #2.
3 200 Heavy particles = Pressure for 100 Light AND 100 Heavy particles will be
__________________ the pressure from Test #3
4 100 Heavy + 100
Light particles =
Pressure for 200 Heavy AND 100 Light particles will be
__________________ the pressure from Test #4.
5 200 Heavy + 100
Light particles =
Pressure for 150 Heavy AND 50 Light particles will be
__________________ the pressure from Test #5.
6 150 Heavy + 50 Light
Write your own prediction:
1. For Test 6 (150 Heavy + 50 Light particles), what is the pressure contribution from the heavy
particles (Pheavy)? How did you figure this out?
2. What is the pressure contribution from the light particles (Plight)? How did you figure this
3. For each test above, calculate the mole fraction of each gas (number of particles of that type /
total particles). Find a relationship between the mole fraction and the pressure contribution of
each type of gas.
4. The atmosphere is composed of about 78% nitrogen, 21% oxygen, and 1% argon. Typical
atmospheric pressure in Boulder, Colorado is about 0.83 atm. What is the pressure contributed
by each gas?