Name
Period
Chapter 24: Thermodynamics
67
Date
Estimating Absolute Zero
The Uncommon Cold
Experiment
Purpose
To use linear extrapolation to estimate the Celsius value of the temperature of absolute zero
Required Equipment/Supplies
safety goggles
paper towel
Bunsen burner
wire gauze
ring stand with ring
250-mL Florence flask
flask clamp
short, solid glass rod
one-hole rubber stopper to fit flask
500-mL beaker
water
thermometer (Celsius)
ice bucket or container (large enough to submerge a 250-mL flask)
ice
large graduated cylinder
graph paper
Optional Equipment/Supplies
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computer
data plotting software
Discussion
Under most conditions of constant pressure, the volume of a gas is proportional to the absolute temperature of the gas. As the temperature of
a gas under constant pressure increases or decreases, the volume
increases or decreases, in direct proportion to the change of absolute
temperature. If this relationship remained valid all the way to absolute
zero, the volume of the gas would shrink to zero there. This doesn’t happen in practice because all gases liquefy when they get cold enough.
Also, the finite size of molecules prevents liquids or solids from contracting to zero volume (which would imply infinite density).
In this experiment, you will discover that you can find out how cold
absolute zero is even though you can’t get close to that temperature. You
will cool a volume of air and make a graph of its temperature-volume
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relation. Then you will extrapolate the graph to zero volume to predict
the temperature, in degrees Celsius, of absolute zero.
Procedure
Set up ice bath.
Step 1: Make an ice bath of ice and water, using a bucket or container
large enough to submerge a 250-mL flask. (Do not put the flask in it yet.)
Step 2: Put on safety goggles. Select a dry 250-mL Florence flask, and fit
a dry single-hole stopper into the flask. Half-fill a 500-mL beaker with
water, set it on the ring stand, and clamp the flask to the ring stand in
the water with the water level approximately 4 cm below the top of the
beaker (see Figure A). Boil the water for at least 3 minutes to make sure
that the air in the flask is heated to the water temperature. Measure and
record the water temperature.
temperature of boiling water = _______________
Step 3: Turn off the burner. Use a damp paper towel to grasp the clamp,
and quickly place a solid glass rod into the hole of the rubber stopper
to trap all the air molecules. Do this quickly while the air in the flask
has the same temperature as the boiling water. Loosen the clamp from
the ring stand, and lift the flask, stopper, and clamp assembly. Allow
the flask to cool for a minute or so until it can be handled comfortably.
Remove the clamp from the flask, and lower the flask upside down into
the ice bath. Hold the flask and stopper below the water surface of the
ice bath, and remove the glass rod.
Fig. A
Record bath temperature.
Step 4: Hold the flask upside down under the water surface for at least
3 minutes. Measure and record the temperature of the ice bath.
Remove flask from bath.
Step 5: Some water has entered the flask to take the place of the contracted air. The air in the flask now has the same temperature as the
ice bath. With the flask totally submerged and the neck of the flask just
under the water surface, place the glass rod or your finger over the hole
of the stopper, and remove the flask from the ice bath.
Measure volumes of air.
Step 6: Devise a method to determine the volume of the trapped air at
both temperatures. Record the volumes.
volume of air at temperature of boiling water = ______
volume of air at temperature of ice bath = ______
Graph and extrapolate.
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Step 7: Plot the volume of air in the flask (vertical axis) vs. the temperature (horizontal axis) for the two conditions. Use a scale of –400 degrees
Celsius to +100 degrees Celsius on the horizontal axis and a scale of 0
mL to 250 mL on the vertical axis. Draw a straight line through the two
points and to the x-axis (where the extrapolated value for the volume of
the gas is zero).
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temperature of ice bath = ______________
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Name
Period
Date
Analysis
1. Why did water flow into the flask in the ice bath?
2. What is your predicted temperature for absolute zero in degrees
Celsius? Explain how the graph is used for the prediction.
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3. In what way does this graph suggest that temperature cannot drop
below absolute zero?
4. What can be done to improve the accuracy of this experiment?
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5. What are some assumptions that you made in conducting the experiment and analyzing the data?
6. What happens to air when it gets extremely cold?
Going Further
Use data plotting software to plot your data. Use the computer-drawn
graph to check your prediction of the temperature of absolute zero.
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7. How does the computer prediction compare with your earlier
prediction?
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