Cell Diagrams for Galvanic Cells (Voltaic Cells) Tutorial
A cell diagram is Chemistry′s short-hand for representing a galvanic cell (voltaic cell).
The usual convention for writing a cell diagram is:
- Single vertical lines, | , indicate a phase boundary or junction
(for example, a solid electrode in contact with a solution)
- Double vertical lines, || , indicate the connection between the two electrolyte solutions such as a salt bridge
- The anode is shown on the left hand side of the diagram
(that is, the oxidation reaction is shown on the left) .
- When the diagram is read from left to right it shows the direction of the electron flow through the galvanic cell (voltaic cell).
For the galvanic cell shown to the right:
- Anode reaction (oxidation):
R(s) → R+(aq) + e-
- Cathode reaction (reduction):
e- + S+(aq) → S(s)
- Electrons, e-, flow from R (which produces R+) to S+ (which produces S) which we might represent as:
R(s) → R+(aq) + e- ↓ e- + S+(aq) → S(s)
R(s) → R+(aq) + e- → e- + S+(aq) → S(s)
- If we substitute the arrow ( →) in the oxidation reaction and in the reduction reaction with the single vertical line representing the phase boundary between the electrode and the solution we get:
R(s)|R+(aq) + e- → e- + S+(aq)|S(s)
- If we then substitute e- → e- with the double vertical lines representing the separation of the two half-cells by the salt bridge we get:
which is the cell diagram for this galvanic (voltaic) cell.
The cell diagram can also be written using the chemical formula for each electrolyte.
For example, if the electrolyte in each half-cell in the example above was a nitrate solution, the cell diagram could be written as :