By
Choong Teow
- Introduction:
Guy-Lussac's Law, which describes a pressure-temperature relationship, states that the
pressure of a gas at constant volume is directly proportional to the absolute temperature. The
following equation express the Guy-Lussac's Law, where "P" is the pressure and "T" is the
The following experiment shows that the dependence of pressure on temperature of dilute
gases with a constant volume is linear for all gases (Gay-Lussac's law). When the pressure vs.
temperature curve is extrapolated to very low temperature, one finds that the pressure is zero
when the temperature is -273.15°C. This significant temperature is used as the basis for the
Kelvin (or absolute) temperature scale, which sets -273.15°C as its zero point (0 K or absolute
zero). The size of a Kelvin unit (called a kelvin) is the same as the size of a degree on the
celsius scale. Thus, the relationship of conversion between the temperatures is simply Tc =
Tk - 273.15. The meaning of absolute zero becomes clear from the kinetic molecular theory
of the ideal gas. Since the pressure of an ideal gas is proportional to the average kinetic energy
of the molecules, when the pressure goes to zero there is no motion of the gas molecules, and
the temperature is at absolute zero.
Procedure:
The Erlenmeyer flask was assembled,
and it was connected to the electronic pressure
transducer - no syringe. This keeps the volume constant. The pressure sensor and the
temperature sensor was connected to the computer. The computer was set up to record
temperature and pressure in event mode. While the measurement was being taken,at least 30
minutes of data acquisition was allowed. The horizontal axis of the graph was set to
temperature and vertical axis to pressure (one volt = one atmosphere). The calibration file that
matches the probe was loaded. The flask was immerged in a large jar of hot (100 deg C) water
and data was begun to be recorded. The apparatus was set up as shown in the diagram below:
In event mode the data was not recorded until the the "keep" button was pressed. Ice was
added gradually to the jar of water to cool the system to 0 deg C. while the acquisition system
is running. The pressure at liquid Nitrogen temperature was obtained. During this step, the
electronic temperature probe should not be immersed in the liquid nitrogen. The pressure of
liquid Nitrogen was used to determine the temperature. The pressure vs.temperature graph was
plot, and the absolute zero was determined. This value was compared to the standard value of
absolute zero. The pressure at liquid Nitrogen temperature was obtained, and this value was
used to determine the temperature of liquid Nitrogen. Precaution step were taken whereby the
electronic temperature probe was
not immerse in the liquid nitrogen.
Results:
The plot of pressure vs. temperature
is as shown below:
Data:
| Time (minute) | Temperature (degree) | Potential (volt) |
| 6.07 | 0.114 | 0.876 |
| 5.99 | 0.185 | 0.876 |
| 10.80 | 9.027 | 0.904 |
| 12.00 | 12.093 | 0.914 |
| 14.80 | 21.861 | 0.946 |
| 17.80 | 32.414 | 0.979 |
| 21.40 | 43.894 | 1.010 |
| 25.30 | 55.445 | 1.050 |
| 28.60 | 63.716 | 1.080 |
| 33.00 | 74.412 | 1.110 |
| 37.40 | 83.752 | 1.140 |
| 43.00 | 91.738 | 1.170 |
This experiment has proven TheGay-Lussac’s Law which says that when the volume is kept
constant, the absolute pressure of a given amount of any gas varies directly with the
thermodynamic temperature. Therefore, as the temperature increases, the pressure also
increases. From the graph, the absolute zero is around –295 degree C when the pressure is
zero. Therefore the absolute zero is rather close to the standard value of absolute zero. The
temperature of liquid nitrogen is around 200 degree C when the pressure is around 0.25V .
Conclusion:
This experiment was considered
successful because the result has proven Charles' Law II
(Guy Lussac Law) which state that the pressure of a gas at constant volume is directly
proportional to the absolute temperature. At constant volume, when the temperature of a gas
increases, the pressure of the gas
also increases proportionally.
Acknowledgement:
Dr. Don Collins for the guidance
and teaching.
Mika
Tanioka for working on the experiment together.
All
physics II coursemates.
Ronald Sebilo-Tibbits.