Although the zinc rod in copper sulfate and the two-solution
cell just described are physically different, the same
chemical reaction takes place in both:
In the cell, however, the 51 kcal of free energy released
by the reaction can be used for other purposes.
Every time a mole of
the above reaction occurs in the cell, two
moles of electrons flow from the zinc anode,
through the external circuit, to the copper cathode.
As we saw previously, in chemical reactions and phase
changes it is useful to define a chemical
potential as the free
energy change per mole of a specific reactant,
as the equation is written.
This chemical potential is the
intrinsic capacity of the reaction to do work;
and the actual work done, or free energy released, is
the product of this potential times the number of moles
of a substance undergoing chemical change.