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Re: Heating/Work



Bob sez the following:

|I think you have a problem using entropy change to distinguish "heating"
|from "working" , Jim.
|Entropy is a state function - its change is independent of "path". A
|moving piston irreversibly compressing a thermally insulated gas DOES
|change the state and the entropy of the gas. (It is true that a
|REVERSIBLE, adiabatic process results in zero entropy change of a CLOSED
|system.)

Ah, yes in deed, but I thought we were viewing this as a reversible change
as all good physicists are wont to do -- if you want to consider
irreversible changes, I don't think that it matters whether one calls the
action Heating or Working -- if deltaS is not readily calculable. The
point is that what ever one lumps into Q should be related to the DS --
and there are many actions which do not involve hot things which might be
included. If the action is not at least arguably reversible, I don't know
how to talk about it meaningfully analytically.

BUT, please, can any further discussion be done privately -- this is not a
popular topic here.


Jim Green
JMGreen@sisna.com
http://users.sisna.com/jmgreen