The maximal, useful work of the osmotic, reversible process is equal
to the change in the Gibbs energy upon mixing. The energy spent toproduce reversible work is provided by the thermal energy of the environment.
The cooling of solutions rather than the change in the Gibbs
energy is the source of energy at the initial stage of mixing in real systems.
In real systems, the cooling should have a minor effect. All theoretical
calculations, based on the Gibbs energy, e.g., [1–6], conserve
their significance, because the value of useful work is calculated in
terms of the change in the Gibbs energy upon transition from the initial
to the final state. The change in the Gibbs energy is independent of the
concrete realization of mixing. The Gibbs energy serves a mathematical
means for calculating useful work. The penetration of water molecules
from the feed solution through the membrane into the draw solution
is due to the gain in statistical distributions. The friction in the membrane
should not lead to work losses because the thermal energy of
the feed solution serves the source of energy spent to overcome friction