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aim1732
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I need a clarification about the reversibility criteria in classical thermodynamics.There are two criteria in it to my understanding.one is that there should be no dissipative forces i.e no friction.The second is that there is no heat flow across a definite temperature gap--only across an infinitesimal temperature difference.The apparent reason given for this is that all processes need to be reversible in a reversible machine and you can not possibly reverse the heat exchange if it occurs a definite temperature gap without causing any other change in the surroundings.I need a little more explanation about this...as in what kind of changes?
Also in the definition of entropy,we talk about reversible heat.Yet when we do work against friction we say that the entropy of the thing we do work on(that gets heated up) rises by the heat supplied divided by the temperature of the body(provided its temperature does not rise much).Is the heat supplied here reversible?Another case is a hot stone being put in a cold reservoir.The heat exchanged here is not reversible;yet we use that heat to calculate the entropy change.
Any help is appreciated.
Also in the definition of entropy,we talk about reversible heat.Yet when we do work against friction we say that the entropy of the thing we do work on(that gets heated up) rises by the heat supplied divided by the temperature of the body(provided its temperature does not rise much).Is the heat supplied here reversible?Another case is a hot stone being put in a cold reservoir.The heat exchanged here is not reversible;yet we use that heat to calculate the entropy change.
Any help is appreciated.