Adapted from Vernier
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Pressure -Temperature
Relationship in Gases
Standards:
1.2.11.A Read and understand the central content of informational texts and documents in
all academic areas.
Use teacher and student established criteria for making decisions and drawing
conclusions
3.2.12 B Evaluate experimental data correctly within experimental limits
3.4.10 A Predict the behavior of gases through the use of Boyle’s, Charles’ or the
ideal gas law, in everyday situations.
3.7.10 C Apply knowledge of advanced input devices.
Introduction and background: Gases are made up of molecules that are in constant
motion and exert pressure when they collide with the walls of their container. The
velocity and the number of collisions of these molecules are affected when the
temperature of the gas increases or decreases. In this experiment, you will study the
relationship between the temperature of a gas sample and the pressure it exerts. Using the
apparatus shown in Figure 1, you will place an Erlenmeyer flask containing an air sample
in water baths of varying temperature. Pressure will be monitored with a Gas Pressure
Sensor and temperature will be monitored using a Temperature Probe. The volume of the
gas sample and the number of molecules it contains will be kept constant. Pressure and
temperature data pairs will be collected during the experiment and then analyzed. From
the data and graph, you will determine what kind of mathematical relationship exists
between the pressure and absolute temperature of a confined gas. You may also do the
extension exercise and use your data to find a value for absolute zero on the Celsius
temperature scale.
Guiding questions: Based on everyday experiences, predict the relationship between the
pressure and temperature of a confined gas at constant volume.
Vocabulary: Absolute temperature is a temperature scale based on absolute zero. Same as
Kelvin temperature scale. It is determined by adding 273 to the temperature value
expressed in the centigrade scale.
Pressure-Temperature Relationship
In Gases
Rev. 5/24/07
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Science In Motion
Wilkes University
Materials:
computer
125 mL Erlenmeyer flask
Vernier computer interface
ring stand
Logger Pro
utility clamp
Vernier Gas Pressure Sensor
hot plate
Vernier Temperature Probe
four 800 mL beakers
plastic tubing with two connectors
glove or cloth
rubber stopper assembly
ice
Safety:
 Wear safety glasses.
 Use caution when handling the hotplate and hot water.
 Do not allow the probe wires to touch the hotplate.
Procedure:
1. Prepare a boiling-water bath. Put about 600 mL of hot tap water into an 800 mL
beaker and place it on a hot plate. Turn the hot plate to a high setting.
2. Prepare an ice-water bath. Put about 500 mL of cold tap water into a second 800 mL
beaker and add ice.
3. Put about 600 mL of room-temperature water into a third 800 mL beaker.
4. Put about 600 mL of hot tap water into a fourth 800 mL beaker.
5. Prepare the Temperature Probe and Gas Pressure Sensor for data collection.
a. Plug the Gas Pressure Sensor into CH1 and the Temperature Probe into CH2 of the
computer interface.
b. Close the 2-way valve above the rubber stopper—do this by turning the valve
handle so it is perpendicular with the valve stem itself (as
shown in Figure 2). The air sample to be studied is now
confined in the flask.
Figure 2
6. Prepare the computer for data collection.
a. Plug the Vernier Lab Pro interface into the power supply.
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b. Attach USB cable to Vernier Lab Pro interface and laptop computer.
c. Power computer.
d. Double click on the Logger Pro icon.
e. Go to the File menu and select Open.
f. Open “Chemistry with Computers.”
g. Click on “07Pressure-Temperature.”
7. Click
to begin data collection.
8. Collect pressure vs. temperature data for your gas sample:
a. Place the flask into the ice-water bath. Make sure the entire flask is covered (see
Figure 2). Stir.
b. Place the temperature probe into the ice-water bath.
c. When the pressure and temperature readings displayed in the meter stabilize,
click
. You have now saved the first pressure-temperature data pair.
9. Repeat the Step-8 procedure using the room-temperature bath.
10. Repeat the Step-8 procedure using the hot-water bath.
11. Use a ring stand and utility clamp to suspend the temperature probe in the boilingwater bath. To keep from burning your hand, hold the tubing of the flask using a
glove or a cloth. After the temperature probe has been in the boiling water for a few
seconds, place the flask into the boiling-water bath and repeat the Step-9 procedure.
Remove the flask and the temperature probe after you have clicked
. Click
when you have finished collecting data. Turn off the hot plate. Record the
pressure and temperature values in your data table, or, if directed by your instructor,
print a copy of the table.
12. Examine your graph of pressure vs. temperature (°C). In order to determine if the
relationship between pressure and temperature is direct or inverse, you must use an
absolute temperature scale; that is, a temperature scale whose 0° point corresponds to
absolute zero. We will use the Kelvin absolute temperature scale. Instead of manually
adding 273 to each of the Celsius temperatures to obtain Kelvin values, you can
create a new data column for Kelvin temperature.
a. Choose New Calculated Column from the Data menu.
b. Enter “Temp Kelvin” as the Name, “T Kelvin” as the Short Name, and “K” as the
Unit. Enter the correct formula for the column into the Equation edit box. Type in
“273+”. Then select “Temperature” from the Variables list. In the Equation edit
box, you should now see displayed: 273+“Temperature”. Click
.
c. Click on the horizontal axis label and select “Temp Kelvin” to be displayed on the
horizontal axis.
13. Decide if your graph of pressure vs. temperature (K) represents a direct or inverse
relationship:
a. If the points are not on the graph, single click on the Autoscale button from the
menu.
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b. Click the Curve Fit button, .
c. Choose your mathematical relationship from the list at the lower left. If you think
the relationship is linear (or direct), use Linear. If you think the relationship
represents a power, use Power. Click
.
d. A best-fit curve will be displayed on the graph. If you made the correct choice, the
curve should match up well with the points. If the curve does not match up well, try a
different mathematical function and click
again. When the curve has a good
fit with the data points, then click
.
e. Autoscale both axes from zero by double-clicking in the center of the graph toview
Graph Options. Click the Axes Options tab, and from the scaling box select
“Autoscale from 0” for both axes.
14. Print a copy of the graph of pressure vs. temperature (K). The regression line should
still be displayed on the graph. Enter your name(s) and the number of copies you
want to print
Data table:
Pressure
(kPa)
Temperature
(°C)
Temperature
(K)
Constant, k
(P / T or P•T)
Calculations: Computer performed calculations and graphing.
Questions:
1. What two experimental factors (variables) must be kept constant during this lab?
2. Based on the data and graph that you obtained for this experiment, write a statement
to express the relationship between gas pressure and temperature.
3. Explain this relationship using the concepts of molecular velocity and collisions of
molecules.
4. Write an equation to express the relationship between pressure and temperature (K).
Use the symbols P, T, and k.
5. One way to determine if a relationship is inverse or direct is to find a proportionality
constant, k, from the data. If this relationship is direct, k = P/T. If it is inverse, k =
P•T. Based on your answer to Question 4, choose one of these formulas and calculate
k for the four ordered pairs in your data table (divide or multiply the P and T values).
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Show the answer in the fourth column of the Data and Calculations table. How
“constant” were your values?
6. According to this experiment, what should happen to the pressure of a gas if the
Kelvin temperature is doubled? Check this assumption by finding the pressure at –
73°C (200 K) and at 127°C (400 K) on your graph of pressure versus temperature.
How do these two pressure values compare?
References: Vernier
___________________________________
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In Gases
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Pressure-Temperature Relationship in Gases
Teacher notes
Time needed to complete lab: This lab can be completed in a 50-60 minute period.
Target grade level: This lab can be performed in a Chem I or Chem II class.
Objectives: The objective is to determine the mathematical relationship between the
pressure and temperature of a confined gas at a constant volume.
Major concepts: This lab can be utilized when teaching gases. It must be emphasized that
quantity and volume of the gas be kept constant.
Preparation: Ice and warm water should be available. Also, it would be expedient to have
the temperature probe, interface and the computer connected.
Typical results or sample data:
Sample calculations:
Answers to questions:
1. The quantity and volume must be kept constant.
2. The pressure of a gas is directly proportional to the absolute temperature of the gas at
constant quantity and volume.
3. As the temperature of the gas increases, the velocity of the molecules increases which
results in an increase of molecular collisions with the surrounding walls. Thus the
pressure increases.
4. P = k T
5. Utilizing k=P/T will produce an relatively constant value.
6. The pressure of the gas is doubled.
Extension: The collected data can also be used to determine the value for absolute zero
on the Celsius temperature scale. Instead of plotting pressure versus Kelvin temperature
as done above, this time plot Celsius temperature on the y-axis and pressure on the xaxis. Since absolute zero is the temperature at which the pressure theoretically becomes
equal to zero, the temperature where the regression line (the extension of the temperaturepressure curve) intercepts the y-axis should be the Celsius temperature value for absolute
zero.
1. Remove the curve fit box on the graph by clicking on its upper-left corner.
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2. Click on the vertical-axis label and select “Temperature” to plot the Celsius
temperature. In the same way, select “Pressure” to be displayed on the horizontal
axis.
3. If the points are not on the graph, single click on the Autoscale button from the menu.
4. Rescale the temperature axis from a minimum of –300°C to a maximum of 200°C.
This may be done by clicking on the minimum and maximum values displayed on the
graph axis and editing them. The pressure axis should be scaled from 0 kPa to 150
kPa. Rescaling can also be achieved by a right click on either axis followed by a left
click on the “Graph Options.” Select the “Axes Options” tab. From the “scaling”
boxes in the x-axis and y-axis locations select “manual” and type the range values.
5. Click the Linear Fit button, . A best-fit linear regression curve will be shown for
the four data points. The equation for the regression line will be displayed in a box on
the graph, in the form y = mx + b. The numerical value for b is the y-intercept and
represents the Celsius value for absolute zero.
6. Print the graph of temperature (°C) vs. pressure, with the regression line and its
regression statistics still displayed. Enter your name(s) and the number of copies you
want to print. Clearly label the position and value of absolute zero on the printed
graph.
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In Gases
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Wilkes University
Science in Motion
Wilkes University
Pressure-Temperature Relationship in Gases
Pre-Quiz
1. What is the relationship between pressure and temperature of a gas?
a.
b.
c.
d.
2.
Predict how the pressure of a confined gas at the Earth’s surface will change if the
confined gas is moved 100 miles above the Earth’s surface.
a.
b.
c.
d.
3.
indirect
direct
not defined
variable
no change
increase
decrease
not predictable
When pressure-temperature data is graphed, the slope produced is
a.
b.
c.
d.
negative
positive
zero
undefined
4. In the study of the gaseous state, how many variables describe the state?
a.
b.
c.
d.
one
two
four
variable
5. Why can not the volume of gas change during the course of this experiment?
a.
b.
c.
d.
It will affect the temperature.
There will be no effect.
The gas will explode.
It will affect the pressure.
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In Gases
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Science In Motion
Wilkes University
Science in Motion
Wilkes University
Pressure-Temperature Relationship in Gases
Post-Quiz
1. In the study of the gaseous state, how many variables describe the state?
a.
b.
c.
d.
variable
four
two
one
2. Why can not the volume of gas change during the course of this experiment?
a.
b.
c.
d.
It will affect the pressure.
The gas will explode.
There will be no effect.
It will effect the pressure.
3. Predict how the pressure of a confined gas at the Earth’s surface will change if the
confined gas is moved 100 miles above the Earth’s surface.
a.
b.
c.
d.
not predictable
decrease
increase
no change
4. What is the relationship between pressure and temperature of a gas?
a.
b.
c.
d.
variable
not defined
direct
indirect
5. When pressure-temperature data is graphed, the slope produced is
a.
b.
c.
d.
undefined
zero
positive
negative
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In Gases
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