Some of the content of this guide was modeled after a guide originally created by Openstax and has been adapted for the GPRC Learning Commons in February 2021.
The YouTube videos on this page are as follows:
1. dnseducation. (2011, December 28). Galvanic Cell.swf [Video]. YouTube. https://www.youtube.com/watch?v=C26pH8kC_Wk
2. W CLN. (2014, November 2). WCLN - Electrolytic cells-type 1 - Chemistry [Video]. YouTube. https://www.youtube.com/watch?v=o8auXrCo_BM
3. Cognito. (2020, May 8). GCSE chemistry - What is corrosion and how to stop it #75 [Video]. YouTube. https://www.youtube.com/watch?v=q0CAfXV-YdY
4. FuseSchool - Global Education. (2016, May 17). How does electroplating work | Reactions | Chemistry | FuseSchool [Video]. YouTube. https://www.youtube.com/watch?v=OxhCU_jBiOA
This work is licensed under a Creative Commons BY NC SA 4.0 International License.
Galvanic Cells or Voltaic Cells
A review of the redox reaction can be found here.
A galvanic cell or voltaic cell consists of the following components, as shown in the figure below:
Figure 1. Galvanic cells and electrodes. From LibreTexts (2021, March 3). Chemistry. https://chem.libretexts.org/@go/page/260
Cell notations are short hand notation of galvanic (or voltaic) cells that describe the following:
Cell Notation Rules
Figure 2. Voltaic Cells. From LibreTexts (2020, August 15). Chemistry. https://chem.libretexts.org/@go/page/285
In the above example:
The reduction half-reaction for the above cell notation is given below. Since Ag+ is gaining electrons, it is being reduced, and this reduction happens at cathode. Since Ag+ is gaining electrons to become Ag, the reactant is Ag+ and it is listed first in the cell notation. The product is Ag and it is listed second for the same half-reaction.
Ag+(aq)+ e− ⇌ Ag(s)
The oxidation half-reaction for the above cell notation is given below. Since Cu is losing electrons, it is being oxidized, which happens at anode. Cu is losing electrons to become Cu2+. Therefore, the reactant is Cu and it is listed first in the cell notation. The product is Cu2+ and it is listed second for the same half-reaction.
Inert and Active Electrodes
An inert electrode is a non-reactive electrode whose primary purpose is to transport electrons. It does not exchange electrons with the solution.
A reactive electrode (such as copper in the above example) is something that participates in the reaction. In the example above, copper is being oxidized to produce Cu2+.
Examples of commonly used inert electrodes: platinum, rhodium, carbon, and gold.
Examples of commonly used active electrodes: copper, sliver, zinc and lead.
Cell potential is the potential difference that exists between two half-cells. It is calculated using the following formula:
where Eo is the standard reduction potential found in your data booklet, as shown below:
Calculating the cell potential for the reaction in the previous section would go as follows:
Cu(s) → Cu2+(aq) + 2e- Eocathode= -0.340 V
Since copper is being oxidized, we use the oxidation half-cell of the redox reaction. Therefore, we reverse the sign of Eo
(Ag+ + e- → Ag(s) ) x2 EoAnode = +0.800 V
This reduction half-reaction is multiplied by two, balancing the number of electrons between both half-reactions.
EoCell = EoCathode + EoAnode
EoCell = 0.800 V + (-0.340 V)
EoCell = +0.460V
Note: Since the cell potential is positive, it is a spontaneous redox reaction!
Voltaic cells are driven by a spontaneous redox reaction which converts chemical energy into electrical energy.
Electrolytic cells, on the other hand, are driven by a non-spontaneous reaction that converts electrical energy into chemical energy. The redox reaction is driven by electrical energy supplied by an external energy source, as shown in the picture below:
Figure 3: The electrolysis of molten sodium chloride. From Openstax (2021) "Electrolysis." Chemistry 2e. https://openstax.org/books/chemistry-2e/pages/17-7-electrolysis
The half-reactions for the figure above are as follows:
Oxidation half reaction : 2Cl-(l) → Cl2(g) + 2e-
Reduction half reaction : Na+(l) + e- → Na(l)
The table below shows the comparison of voltaic cells and electrolytic cells:
Voltaic (Galvanic) Cell or Electrochemical Cell
Converts chemical energy into electrical energy
Converts electrical energy into chemical energy
Spontaneous redox reaction
Non-spontaneous redox reaction; electrical energy is used to drive the reaction
Anode is negative, and cathode is positive. Oxidation happens at the anode and reduction happens at the cathode.
Anode is positive and cathode is the negative. Oxidation happens at the anode and reduction happens at the cathode.
Electrons come from the oxidized species and go from anode to cathode in the external circuit.
Electrons are supplied by the external power source. They enter through the cathode and come out through the anode.
Half-cells are set up in different containers and are connected using a salt bridge or porous partition.
The electrodes, both anode and cathode, are placed in one container in a solution of molten electrolyte.