University of Virginia
Physics Department

## Determining Absolute Zero

A Physical Science Activity

Adapted from: Meridian Creative Group, a Division of Larson Texts, Inc. (1996). CBL Explorations in Chemistry for the TI-82 and TI-83

2003 Virginia SOLs

• PS.1
• PS.7

Objectives

Students will

• use Calculator-Based Laboratory (CBL) equipment to measure temperatures and pressures of gas samples;
• graph pressure vs. temperature plots;
• extrapolate graphs to determine the value of absolute zero.

Motivation for Learning

Driving Question

Is there a limit to how cold something can get? What would make an object stop getting colder? What is this limit, and how can we find it?

Background Information

Temperature is a measure of the kinetic energy (or movement) of particles inside of an object. If particles have a lot of kinetic energy, the object will have a high temperature, and if particles have less kinetic energy, the object will have a low temperature. So, the lowest temperature an object can have happens when the particles in the object are not moving at all. We call this temperature absolute zero. This is zero Kelvin (the SI unit for temperature), and -273 C° on the Celsius scale. When particles in a gas stop moving and are at this point of absolute zero, the pressure of that gas is also zero. If particles are not moving, they are not bouncing around and hitting their container, so there is no pressure being exerted. In this activity, students will measure pressures and temperatures of gas samples, make a graph, and then extrapolate the data to determine the temperature at zero pressure. This should give them the temperature at absolute zero.

### Student Activity

Materials

• CBL
• TI-83 Graphing Calculator
• CHEM-BIO program from Vernier loaded on the calculator
• Vernier Pressure Sensor with syringe and CBL DIN adapter
• Temperature Probe
• 2 rubber bands or tape
• Hot plate
• 4 beakers to be filled with water of different temperatures
• boiling water
• warm water
• room temperature/cool water
• ice water
• Graph paper
• Ruler

Procedure

1. Place 2 beakers of water on hot plate. Leave one on long enough to get warm water and leave the other on long enough to begin boiling.
2. Fill a third beaker with room temperature/cool water and a fourth with cool water and ice.
3. While water is warming up, set up the CBL, calculator, and other equipment as in the following figure.

4. Connect the CBL and TI-83 calculator with the black link cable. Use the piece of tubing to connect the syringe to the pressure sensor and the CBL DIN adapter to connect the pressure sensor to the CBL. Open the blue valve on the pressure sensor to open the syringe to the outside air. Fill the syringe to 10cc of air and then turn the blue valve to close off the syringe to the outside air. Connect the pressure sensor to channel 2 (CH2). Connect the temperature probe to channel 1 (CH1) on the CBL. Attach the temperature probe to the syringe using the rubber bands or tape so that they will stay together when you are taking measurements.
5. Once all of your equipment is connected, and the water baths have reached appropriate temperatures, begin the data collection program.
6. Turn on the TI-83 calculator and the CBL. Press the PRGM button on the calculator to get a listing of your programs. Move your cursor or press the correct number to select the CHEMBIO program. Press ENTER again to start program. Follow the directions on the screen until you reach the main menu for the program.
7. Choose SET UP PROBES from the list. The CBL screen should have three dashes across it (to signify communication between it and the calculator) and the calculator should then give you a prompt for the number of probes being used. In this case we are using the pressure and temperature probes, so we will press 2 and ENTER.
8. Next you will need to select the correct probes and channel numbers. Remember the temperature probe is in CH1 and the pressure probe is in CH2.
9. The stored calibration for the pressure sensor should work. If you are getting reasonable data, use it and ATM for the units. If you are getting bad data, you may need to calibrate the pressure sensor. Select the manual entry option. For atmospheres, the intercept is 0.729 and the slope is 0.271. If you wish to use a different unit, you can find the calibration numbers on the Vernier website (www.vernier.com).
10. You should now be back at the main menu for the program. Now we want to choose COLLECT DATA and then choose MONITOR INPUT. At this point, both the CBL and calculator should be showing readings from the probes.
11. Now we want to place the syringe and temperature probe into the first temperature bath. Start with the ice water because it is easier to warm up the temperature probe than it is to cool it down. Make sure you do not get the pressure probe itself wet. Just put the syringe into the water.
12. Watch the readings on the calculator. Once they stabilize, record readings of temperature (in Celsius) and pressure in data table.
13. After these numbers have been recorded, move the syringe to the room temperature/cool water bath. Again, wait for the readings to stabilize and record them in the data table. Repeat these steps for the warm water and boiling water baths.
14. Once you have done all four baths, press the + button on the calculator to stop the readings. Disassemble and clean up all of your equipment.
15. Convert temperature readings to Kelvin and record those in the data table.
16. Make a graph of pressure (Y-axis) vs. Kelvin temperature (X-axis), start at 0,0.
17. Draw a line to best fit the shape of the graph. Continue this line so that it passes through a pressure reading of zero (crosses the x-axis). Read this temperature and record this as the value for absolute zero.

Data Sheet

Data Table

 Bath Temperature (°C) CH1 Pressure (atm) CH2 Temperature (K) Ice Water Room Temp/Cool Water Warm Water Boiling Water

Absolute zero = ______________K

Extensions

1. Have students run the program on the calculator so that the points will be plotted for them. Take them through the steps to find a best fit line and have the calculator draw the line for them. They can then trace this line to find where absolute zero occurs.
2. Have students repeat the activity with a different gas. Some suggestions are helium (used to fill up balloons) or carbon dioxide from dry ice. The slopes of the lines should be different, but they should all converge at absolute zero.

Students with Special Needs

All students should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

Assessment

1. Walk around and check the students' graphs to make sure they are doing them correctly.
2. Have students write a conclusion to the experiment. They should explain what absolute zero is and how they went about determining the value of it. They should also explain what the graph shows. What sort of relationship is there between pressure and temperature? What is the lowest possible temperature we could ever reach? What are some sources of error in the experiment? If they had to do the experiment over, what are some changes they could make for it to be more accurate?