Take the tour ×  A process is reversible if and only if it's
always at equilibrium during the process. Why?  I have heard
several specific example of this, such as adding weight
gradually to a piston to compress the air inside reversibly, by
why should it be true in general?  EDIT: Here is something that
would firmly convince me of this: Suppose I have a reversible
process that is not always in equilibrium. Describe a mechanism
for exploiting this process to create a perpetual motion
machine.  share|improve this question I've removed my answer for
the time being, since I agree, it's not terribly clear about
things. Will hopefully get some time to expand and edit later.
–  Noldorin Nov 4 '10 at 13:05 looking forward to it –  Mark
Eichenlaub Nov 4 '10 at 18:18 add comment  4 Answers  up vote 6
down vote accepted  I guess the simplest answer is just to
carefully read you own words again. A reversible process is the
one that can be made flow backwards. It is intuitive to think
that it can be made flow backwards a