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I've done some searching on google and wikipedia, but I can't seem to find anything. What is the quasi static process on an ideal monatomic gas where there is a decrease in entropy?

Thanks

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marked as duplicate by Community Feb 12 '18 at 22:45

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  • $\begingroup$ Slowly cooling it down while keeping its volume constant. $\endgroup$ – probably_someone Feb 12 '18 at 4:18
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A quasi static process means to go from a state A to a state B passing through a lot of intermediate equilibrium states (or almost equilibrium states). A transformation that isn’t of this type can’t be described by usual thermodynamic means. In concrete terms it means that changes you are making happens slowly with respect to the microscopic motion of particles.

If you compress an ideal gas at constant temperature, the heat would leave the system (because you are doing work against pressure and energy is conserved), hence entropy variation dS = dQ/T < 0. If you think about it, entropy can be interpreted as a measure of the number of microscopic configurations associated with the same macroscopic state. If you reduce volume at constant temperature the number of particles configurations decrease (there is less space to move, and energy is the same because temperature didn’t increase).

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