Further observations
Maintaining a particle at constant
temperature, as its accessible volume increases,
allows it to do work equal to T times the logarithm of the
volume increase factor, but only if the particle is confronted
by an appropriate potential for it to do work against.
In the following pages we first present some oversimple models
that demonstrate the concept of ergodic pumping, but
only demonstrate a few kT of work being done by the expansion.
We then present models with additional potential terms and show
how several kT of useful work can be extracted during an expansion.
One feature of these latter models is that they predict that
the external work on a load is done before the ADP-P bond
is severed, by coupling that external work to the binding together
of two components, which the ADP and P subsequently push apart again.