LECTURE PHYSICAL CHEMISTRY 3rd EDITION ROBERT G. MORTIMER

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The Joule Experiment
The first attempt to determine whether (∂U/∂V) T ,n vanishes for
real gases was made by Joule around 1843. His apparatus is
schematically depicted in Figure 2.5.
Because the surroundings were not affected during the
expansion into a vacuum, w was equal to zero. The gas
expanded rapidly so there was little opportunity for heat to be
transferred to or from the surroundings, and q therefore
vanished to a good approximation. From the first law, ∆U was
equal to zero. If a change in temperature of the gas occurred,
heat would be transferred to or from the surroundings after the
expansion was complete, and the final temperature of the
surroundings would differ from the initial temperature. If the
heat capacity of the apparatus and the heat capacity of the gas
are known, the change in temperature of the gas could be
calculated.
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