The electrochemical cells we have looked at so far have all involved spontaneous redox reactions. In such galvanic cells electron transfer occurs during chemical change. When the electrons are diverted to some kind of device electrical work may be done. Under completely reversible conditions (i.e., if the work is done verrrrrrrrry slowly), all of the energy in the reaction is released as free energy.
But there is another kind of
electrochemical process in which electrical work must be done on
a chemical mixture in order to make a reaction occur. If the
electrical work is stopped, the reaction stops. Such a process is
non-spontaneous. The free energy change is positive and
the Eo is negative. Cells in which reactions
like this take place are called electrolytic.
Although at first such
processes might not seem very useful they are sometimes the only
way to obtain certain elements. Some very useful commercial and
ornamental processes such as plating are also electrolytic in
nature. Electrolysis can be roughly divided into three
categories.
