http://www.ck12.org Chapter 20. Gas Laws
FIGURE 20.7
An ideal gas thermometer can be used to
easily find temperatures in Kelvins.Absolute Zero
Before the advent of the Kelvin scale, scientists generally used the Celsius scale. They also used gas thermometers
which operated according to the same principles as the one described above. As shown below, a Celsius scale gas
thermometer also replicates the linear relationship between volume and temperature.
Because of practical limitations, they could not create temperatures near what we called absolute zero above, but
by extrapolating from observed regions, they found that hypothetically, an ideal gas would have zero volume at a
temperature of about−273 degrees Celsius. This is how the concept ofabsolute zerowas first identified:
QuestionsSince the gas laws as we introduced them use Kelvins, they could not have been used before the Kelvin scale
was around. Using formula [1], show how each of the gas laws and the combined law would be modified for
Celsius units. Indeed, this is how the empirical gas laws were first formulated. Explain the graph above and
how and why the switch to Kelvins might have occurred in terms of your answer to the question above.Answer
The gas laws still hold in their general relationships; Boyle’s law, being temperature-independent, remain
unchanged. The other two laws are still linear relationships, but now there is anx-intercept (work out the
algebra). The Kelvin scale can be explained as a way to eliminate thex-intercept found in various temperature-
dependent phenomena, such as the gas laws. Also, note that — as suggested by the discussion on scales above
— converting between any two temperatures scales with zeroes calibrated to absolute zero will be as simple
as converting between length or time scales.