Consider n moles of a gas, initially confined within a volume V and held at temperature T. The gas is expanded to a total volume aV, where a is a constant, by (a) a reversible isothermal expansion and (b) removing a partition and allowing a free expansion into the vacuum. Both cases are illus- trated in Fig. 14.9. Assuming the gas is ideal, derive an expression for the change of entropy of the gas in each case.

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Ideal gas case only please

Consider n moles of a gas, initially confined within
a volume V and held at temperature T. The gas
is expanded to a total volume aV, where a is a
constant, by (a) a reversible isothermal expansion
and (b) removing a partition and allowing a free
expansion into the vacuum. Both cases are illus-
trated in Fig. 14.9. Assuming the gas is ideal,
derive an expression for the change of entropy of
the gas in each case.
(a)
(b)
V
gas
(a-1)V
partition
V
(a-1)V
gas
vacuum
Fig. 14.9 Diagram showing n moles of gas, initially
confined within a volume V.
Repeat this calculation for case (a), assuming that
the gas obeys the van der Waals equation of state
n²a
(p+ ²) (V - nb) = nRT.
(14.55)
Show further that for case (b) the temperature of
the van der Waals gas falls by an amount propor-
tional to (a
1)/a.
Transcribed Image Text:Consider n moles of a gas, initially confined within a volume V and held at temperature T. The gas is expanded to a total volume aV, where a is a constant, by (a) a reversible isothermal expansion and (b) removing a partition and allowing a free expansion into the vacuum. Both cases are illus- trated in Fig. 14.9. Assuming the gas is ideal, derive an expression for the change of entropy of the gas in each case. (a) (b) V gas (a-1)V partition V (a-1)V gas vacuum Fig. 14.9 Diagram showing n moles of gas, initially confined within a volume V. Repeat this calculation for case (a), assuming that the gas obeys the van der Waals equation of state n²a (p+ ²) (V - nb) = nRT. (14.55) Show further that for case (b) the temperature of the van der Waals gas falls by an amount propor- tional to (a 1)/a.
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