The voltage of an electrochemical
cell or battery is a familiar concept. It measures the
potential for doing useful work with the cell.
The actual amount of work
done is the product of this potential
times the amount of chemical
reaction carried out through the cell; just as
the amount of work that can be harnessed from a waterfall
depends on the height of the waterfall (analogous
to potential, E), and the amount of water that
flows over the falls (analogous
to electrons, nF).
For both waterfalls and electrochemical cells, the
product of potential drop and quantity of matter reacted
is the free energy released in the process, D