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Question 16.5: An adiabatic expansion Now let’s consider the trivial case o...

An adiabatic expansion

Now let’s consider the trivial case of a gas that expands adiabatically and reversibly. What is its change in entropy?

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SET UP AND SOLVE In an adiabatic process, no heat enters or leaves the system; Q = 0, and there is no change in entropy: ΔS = 0. Every reversible adiabatic process is a constant-entropy process.

REFLECT The increase in disorder resulting from the gas occupying a greater volume after the expansion is exactly balanced by the decrease in disorder associated with the lowered temperature of the gas and its decreased molecular speeds.

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