Electrochemical Cells

The concept of separating a redox reaction into separate reduction and oxidation parts is not purely
a theoretical mechanism to help in this paper-and-pencil task. In real life, one can often actually
carry out the two half-reactions in separate compartments or beakers, and couple the two so that
the electrons are forced to flow through an external circuit. Such a configuration occurs in the
galvanic cell, one class of electrochemical cells.

An electrochemical cell is a contained system in which a redox reaction occurs in conjunction with
the passage of electric current. There are two types of electrochemical cells, galvanic cells (also
known as voltaic cells) and electrolytic cells. (We shall investigate the differences between the two
types shortly.) Both kinds of electrochemical cells contain two electrodes, which are essentially two
pieces of metal, that serve as the sites for the oxidation and reduction half-reactions separately. The
electrode at which oxidation occurs is called the anode, and the electrode at which reduction occurs
is called the cathode. This is true for both galvanic (voltaic) and electrolytic cells.

GALVANIC CELLS

A redox reaction occurring in a galvanic cell has a negative ∆G and is therefore a spontaneous
reaction. Galvanic cell reactions supply energy and are used to do work. This energy can be
harnessed by placing the oxidation and reduction half-reactions in separate containers called half-
cells. The half-cells are then connected by an apparatus that allows for the flow of electrons. The
spontaneous flow of electrons is forced to go through external circuitry in which their potential
energy is extracted.

A common example of a galvanic cell is the Daniell cell, shown below: