# Gas Properties Simulation Activity Worksheet Answer Key

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Page 1
Under Pressure: A Gas Properties Homework Activity
This activity is designed to help us determine the relationships between the physical
properties of gasses, pressure, volume, number of moles, and temperature. We will investigate how
a change in one of these properties will affect the rest. The heavy species you will see are a model
representation of N2 gas molecules. The N2 gas molecules are shown as blue spheres for simplicity.
In reality, we know that N2 molecules are not blue spheres.
This exercise is long but you will not be asked to complete the entire thing. Depending on
where your last name falls in the alphabet you will be responsible for a different section of the
material, as outlined in the chart below. Be sure to take good, clear notes on your results as we will
all be sharing the data during the next class period.
Everyone must complete part I. In addition to part one:
Last Name Additional Part to Complete
A-D Part II
E-G Part III
H-J Part IV
K-R Part V
S-Z Part VI
The website address for the simulation is http://phet.colorado.edu/en/simulation/gas-properties You
can either download it and run it from your computer or run it online by clicking “Run Now!”
Note: Steps to perform with simulation are in BOLD, questions to answer are in ITALICS.
Part I: What units are used to measure temperature, and pressure? How
does speed and size of molecules compare to speed and size of familiar
objects?
Add 100 N2 molecules to the box. To do this, go to the window next to “Heavy Species”. Enter
“100” and hit enter key. You can also pump the handle on the bicycle pump by clicking on it
and dragging.
What is the temperature of the gas molecules?
Tgas(K) = __300K___________________
The temperature is given on the Kelvin scale. What would this temperature be on the Celsius scale?
Tgas(°C) = ___26.85 °C_________________
How does this compare to the temperature of the room you are in?
This is very comparable to room T! Room T is usually around 25°C or 75°C
What is the pressure in the box?
Pbox(atm) = ____0.52 atm________________
How does this compare to the pressure exerted on you by the air around you?
This is less than the external pressure, which is closer to .8 atm (80% of sea level pressure)
Page 2
Pause the simulation. Under “Measurement Tools” choose “ruler”. The ruler is in units of
nanometers. Click and drag the ruler to measure the diameter of a heavy molecule.
What is the diameter of one heavy blue molecule in nm? In m?
diametermolecule(nm) = ___0.2 nm__ diametermolecule(m) =__2E-10 m___
The tip of a pencil is about 0.5 mm across.
How many heavy molecules could line up across the tip of a pencil?
0.5mm or 5E-4m/2E-10m = 2.5E6 molecules
Hit “PLAY” to restart motion.
Under “Measurement Tools”, choose “Species Information”.
What is the average speed of the molecules?
Avg. Speed (m/s) = ____420 m/s________________
Are these molecules moving faster or slower than a car driving 60 miles/hour?
60 mi/hr * (1hr/3600sec) *(5280ft/mi)*(12in/ft)*(2.54cm/in)*(1m/100cm) ~ 26.8 m/s
OR
420m/s*(3600sec/hr)*(100cm/m)*(1in/2.54cm)*(1ft/12in)*(1mi/5280ft)~940mi/hr
Therefore, the molecule is moving faster by almost a factor of 20.
Are these molecules moving faster/slower than a supersonic jet traveling at 2000 miles/hour?
The molecule is moving slower by about a factor of 2
How long will it take a heavy molecule to travel 100 meters? (This is approximately the length of a
football field.)
Time to travel 100 meters (s) = ____.24s__________
Now that we have a frame of reference for how big molecules are and how fast they are moving, we
will investigate the relationships between their properties. In looking for a relationship between any
2 properties, we hold all other variables constant. One property (the independent variable) is
adjusted, and the impact on another property (the dependant variable) is observed. You do not
directly control the dependant variable, but it will change as a result of adjustments you make to the
independent variable. Remember that you only have to complete your section, but feel free to play
around with changing any of the other variables once you have your necessary data.
Page 3
Part II: Pressure versus Volume – Two Properties Enter, One Property Leaves
Predict: What will happen to the pressure in a sealed container if you increase the volume, while
keeping the temperature and number of molecules in the container constant?
The pressure will decrease and will go as 1/V
Sketch the relationship between pressure and volume on the graph below. When graphing
variables, the independent variable goes on the x-axis and the dependant variable goes on the y-axis.
Be sure to label the axes with the variable name and corresponding units, example: pressure (atm)
and volume (liters)
Under “Measurement Tools”, choose “Ruler”
Measure the width of the box using the ruler.
Width box (nm)=______6.6 nm_______________
Under “Measurement Tools”, choose “Layer Tool”. Move the bar to the top of the box. What is
the height of the box?
Height box (nm) = _____5.4 nm (may have 5.3 nm)_______
Click “Pause” and then “Reset”
In the “CONSTANT PARAMETER” section click “TEMPERATURE”.
Change the width by clicking the handle on the left wall, and moving it left or right. Using the
ruler, set the box width to 3 nm.
Add 100 heavy molecules and hit enter.
Once pressure and temperature have stabilized record the following data. Then move the wall
to a new width and record the temperature and pressure. Make sure pressure and
temperature have stabilized before you record new values.
Table 1.
Number T (K) P (atm) Width (nm) Volume (nm3)
(see below)
Run 1 100 300 0.85 4 216
Run 2 100 300 0.70 5 270
Run 3 100 300 0.53 6 324
Run 4 100 300 0.50 7 378
Run 5 100 300 0.43 8 432
Page 4
If the width of the box is doubled, what happens to the volume?
The volume doubles
Here only two dimensions, width and height, are visible. You have already measured both of them.
Assume the depth of the box is 10.0 nm.
Calculate the volume of the box for each run and enter the values into Table 1.
What variable(s) did you adjust?
Adjusted the volume
Besides the variable(s) you adjusted, what other variable changed?
The pressure changed
Write one sentence describing how volume and pressure are related.
As the volume is increased the pressure decreases. The change in pressure goes as 1/V
What is the mathematical relationship between volume and pressure?
PV = constant
Use EXCEL to make a graph of your Pressure vs. Volume data.
Does the graph you sketched in the Predictions section agree with the graph of your data? Describe
any differences. Yes they agree
Part III: Pressure versus Number of Moles – No Holds Barred
Predict: What will happen to the pressure if you add more molecules to the sealed container, while
holding temperature and volume constant?
The pressure will increase linearly if you increase the moles/molecules of gas
Sketch the relationship between pressure and number of molecules on the graph below.
Hit the “RESET” button.
Make sure “TEMPERATURE” is clicked under constant parameters.
Add 100 heavy molecules to box.
Page 5
Once pressure has stabilized record the following data. Change the number of molecules, wait
for the pressure to stabilize again, and record the new data.
Table 2. Number T (K) P (atm) Width (nm)
Run 1 100 300 0.37 6.6
Run 2 200 300 0.78 6.6
Run 3 300 300 1.12 6.6
Run 4 400 300 1.55 6.6
Run 5 500 300 1.82 6.6
NOTE numbers could change depending on the width of the box and therefore, the volume
What variable did you adjust?
The number of N2 molecules
Besides the variable you adjusted, what other variable changed?
The pressure increased
Write one sentence explaining how pressure and number of molecules are related.
As you increase the number of molecules the pressure responds in a linear fashion
What is the mathematical relationship between pressure and number of molecules?
P/no. molecules=constant
Use EXCEL to make a graph of the relevant variables.
Does the graph you sketched in the Predictions section agree with the graph of your data? Describe
any differences. Yes, they are similar
Part IV: Pressure versus Temperature – A Fixed Volume Cage Match
Predict: What will happen to the pressure if you increase the temperature of the sealed container at
a constant volume?
The pressure will increase linearly if you increase the temperature
Sketch the relationship between pressure and temperature on the graph below.
Hit the “RESET” button.
Make sure “Volume” is clicked under constant parameters.
Under “measurement tools” choose “species information” to view the average speed
Add 100 heavy molecules to box.
Page 6
Once pressure has stabilized record the following data. Then change the temperature by
adding or removing heat using the slider below the box. Wait for the pressure to stabilize
again, and record the new data.
Table 3 T (K) P (atm) # molecules Average Speed (m/s)
Run 1 100 0.20 100 245
Run 2 200 0.34 100 345
Run 3 300 0.55 100 420
Run 4 400 0.69 100 480
Run 5 500 0.84 100 545
What variable did you adjust?
Temperature
Besides the variable you adjusted, what other variable changed?
The pressure and average speed increased
Write one sentence explaining how pressure and number of molecules are related.
As you increase the temperature, the pressure responds in a linear fashion
Write one sentence explaining how temperature and pressure are related.
As the T doubles so does the pressure
What is the mathematical relationship between temperature and pressure?
P/T = constant
Use EXCEL to make 2 graphs. In one, demonstrate the relationship between pressure and
temperature. In the second, show the relationship between average speed and temperature. The first
should be linear just like in the predictions and the second should be v α (T)1/2
Does the graph you sketched in the Predictions section agree with the graph of your Pressure vs
Temperature data? Describe any differences. They are similar
Part V: Volume versus Number Of Moles – Too Many Cooks In The Kitchen
Predict: What would happen to the volume of a sealed container if you increased the number of
moles of gas at a constant pressure (think of a container with a piston).
The volume will increase directly with number of moles.
Sketch the relationship between Volume and # of moles on the graph below.
V
ol
um
e
(c
m
^3
)
# of Moles
Volume vs # Of Moles
Page 7
Hit the “RESET” button.
Make sure “Pressure” is clicked under constant parameters.
Under “measurement tools” choose “ruler” to be able to measure the length of the box
Add 70 heavy molecules to box.
After each addition be sure that the temperature is still at 300K, adjust as necessary.
Once pressure has stabilized record the following data. (It may be helpful to pause the
simulation)
To calculate the Volume of the box, assume the depth of the box is 10nm
Table 4 T (K) P (atm) # molecules Length Of Box (nm) Volume Of Box (nm3)
Run 1 300 0.84 70 2.9 156.6
Run 2 300 0.86 90 3.5 189.0
Run 3 300 0.85 110 4.4 237.6
Run 4 300 0.85 130 5.2 280.8
Run 5 300 0.84 150 5.9 318.6
What variable did you adjust?
Number Of Molecules
Besides the variable you adjusted, what other variable changed?
The width of the box and hence volume changed
Write one sentence explaining how temperature and pressure are related.
As the number of molecules doubles so does the volume
What is the mathematical relationship between volume and number of moles?
V/n = constant
Use EXCEL to make a graph of the relationship between number of molecules and volume. The
graph should be linear increasing
Does the graph you sketched in the Predictions section agree with the graph of your Volume vs
Number of Molecules data? Describe any differences. They are similar
Part VI: Volume versus Temperature – If you can’t stand the heat…
Predict: What would happen to the volume of a sealed container if you increased the temperature of
the gas at a constant pressure (think of a container with a piston).
The volume will increase directly with temperature.
Sketch the relationship between pressure and temperature on the graph below.
V
ol
um
e
(c
m
^3
)
Temperature (K)
Volume vs Temp
Page 8
Hit the “RESET” button.
Make sure “Pressure” is clicked under constant parameters.
Under “measurement tools” choose “ruler” to be able to measure the length of the box
Add 100 heavy molecules to box.
Once pressure has stabilized record the following data. Then change the temperature by
adding or removing heat using the slider below the box. Wait for the pressure to stabilize
again, and record the new data.
To calculate the Volume of the box, assume the depth of the box is 10nm
Table 5 T (K) P (atm) # molecules Length Of Box (nm) Volume Of Box (nm3)
Run 1 200 0.86 100 2.5 135.0
Run 2 250 0.86 100 3.3 178.2
Run 3 300 0.85 100 3.9 210.6
Run 4 350 0.85 100 4.6 248.4
Run 5 400 0.84 100 5.6 302.4
What variable did you adjust?
Temperature
Besides the variable you adjusted, what other variable changed?
The width of the box and hence volume changed
Write one sentence explaining how temperature and pressure are related.
As the temperature doubles so does the volume
What is the mathematical relationship between volume and temperature?
V/T = constant
Use EXCEL to make a graph of the relationship between volume and temperature. The graph
should be linear increasing
Does the graph you sketched in the Predictions section agree with the graph of your Volume vs
Temperature data? Describe any differences. They are similar