Absolute Zero

 

Summary: 

The pressure in a closed system is measured at different temperatures.  The resulting data are plotted on an overhead and absolute zero is extrapolated.

Hazards: 

Acetone is flammable

Dry ice is very cold.  Avoid contact with living tissue.

Chemicals and Solutions: 

Dry ice

Acetone

Ice

Materials: 

3 ea 2L beakers large enough to contain and submerge metal bulb

T vs. P apparatus (sealed metal bulb with differential pressure gauge)

Hotplate (for heating water)

Large beaker of hot water

Large beaker of ice water

Large beaker of dry ice & acetone

Appropriate Thermometers

Overhead with x as pressure, y as temperature (ranges?)

Procedure: 

Pressure at Room Temperature:

Measure room temperature using the digital thermometer.  Measure pressure at room temperature. The differential pressure gauge uses atmospheric pressure as 0psi.  Add about 15psi (estimating atmospheric pressure) to get the total pressure

Pt = Pa + Pm

where Pt is total pressure, Pa is atmospheric pressure, and Pm is measured gauge pressure.

Pressure at 100oC:

Heat water on the hotplate until it maintains a rolling boil.

Completely immerse the bulb of the T vs. P apparatus in the boiling water.  The gauge pressure will increase to about 22psi.  Record the gauge pressure and again add in atmospheric pressure, expect a total pressure near 37psi.

Pressure at 0oC:

Immerse the bulb of the T vs. P apparatus in the ice bath.  The gauge pressure will drop (to about 13psi).  Add atmospheric pressure, for a total near 28psi.


Pressure at –78oC:

Immerse the bulb of the T vs. P apparatus in the dry ice acetone bath.  Record the temperature (about –78oC).  The gauge pressure will drop (to about 5psi).  Record the gauge pressure and add in atmospheric pressure (total pressure 20psi).

Make a graph of temperature vs. total pressure and extrapolate back to 0psi to determine absolute zero temperature.

 

To schedule a demonstration, please send an email to the demonstration lab.

 

Contact:

Eric Camp

Lecture Demonstration Technician

Bagley Hall 171

(206) 543-1606

ericcamp@uw.edu

 

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