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> aren't reversible processes necessarily near equilibrium?
No.
Recall the previous example: A fuel cell. The
reverse of this is plain old electrolysis. The
forward and reverse reactions can be pretty close
to reversible. In practice they are much more
nearly reversible than any heat engine you're
likely to see. The efficiency of the fuel cell
is incomparably greater than what you would get
from taking the same fuel (H2 and O2), burning
it to make heat, and running a heat engine.
The reactants have a great deal of energy and
relatively little entropy. Burning gratuitously
creates much more entropy, and then later you
have to pay a terrible price to unload this
entropy (via the waste-heat exhaust port on
your heat engine).
If you try to guess the efficiency of the fuel
cell using the thermodynamic formula, based
on the highest temperature and lowest temperature
in the fuel cell, you are going to be wrong
by orders of magnitude. The W+Q law is misleading
or at best inapplicable. The real laws of
physics (conservation of energy and nondecrease
of entropy) remain true and applicable.
As another example: the biochemical reactions
that convert, say, glucose to ATP and vice versa
are much more efficient than you would think
if you considered them as heat engines that
"burn" the glucose.
There are many other examples of processes that
are reversible but not heat-based.