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Physics
Classical Physics
Thermodynamics
Entropy of system and surroundings
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[QUOTE="Chestermiller, post: 5474156, member: 345636"] If a closed system is subjected to a reversible process, there is no guarantee that the surroundings is also handled reversibly during the process. For example, if you bring about an adiabatic reversible compression of a gas within a cylinder by hand (say by very gradually subjecting the gas to increasing pressure using a piston attached to a rod being pushed by your hand), the [URL='https://www.physicsforums.com/insights/grandpa-chets-entropy-recipe/']change in entropy[/URL] of your body (which basically constitutes the surroundings) certainly will be positive. On the other hand, if the same change is brought about by sliding tiny weights onto the piston at different elevations, the [URL='https://www.physicsforums.com/insights/grandpa-chets-entropy-recipe/']change in entropy[/URL] of the surroundings will be zero. Moran et al, Fundamentals of Engineering Thermodynamics define "Internally Reversible Processes." These are processes for which the system experiences a reversible change without specifying whether the surroundings are handled reversibly or irreversibly. If you want to make sure that the surroundings is always handled reversibly during all changes you consider, I have a special tool kit that one can use. It consists of two kinds of items: (a) a set of tiny weights that can be applied to change the pressure gradually and (b) an infinite array of constant temperature reservoirs at different temperatures, so that the system can be contacted with a sequence of reservoirs at gradually increasing- or gradually decreasing temperatures. This should do the trick. Chet [/QUOTE]
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Entropy of system and surroundings
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