# Physics

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

conceptual understanding.

Part I: Explore the Simulation

Take about five minutes to explore the sim. Note at least two relationships that you observe and

find interesting.

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.

Tips:

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

(~100-200)

Kinetic

Energy

Distribution

sketch for T1

Speed

Distribution

sketch for T1

Kinetic

Energy

Distribution

sketch for T2

Speed

Distribution

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

distributions?

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

or

inversely proportional

volume, temperature directly proportional

or

inversely proportional

volume, number of

gas particles

directly proportional

or

inversely proportional

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.

Test

#

Pressure

Measurement

Pressure Prediction

(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

particles =

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

out?

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?

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