facebook

Electrolytic vs Galvanic Cell
Electrochemistry for the MCAT

William Cohen
Published by William Cohen
Last Updated On: December 3, 2021

MCAT is the test needed for admission to most medical schools, which is why you want to get a good score on this test.

To get a good MCAT score, you should cover all areas tested on the MCAT. One of the areas is electrochemistry.

I often have students asking for help in this area. I’ve decided to use everything I’ve learned during the 12 years of MCAT tutoring to bring you an electrochemistry guide.

I’ll talk about everything you should know concerning galvanic vs. electrolytic cells.

Electrolytic Cells vs Galvanic Cells Summary

  • Electrochemistry is important because it powers cells in the body.
  • Galvanic cells have a spontaneous reaction.
  • Electrolytic cells have a nonspontaneous reaction.
  • There are several differences and similarities between these two types of cells.

Electrochemistry

Electrochemistry concept

Electrochemistry studies chemical processes and how they cause electrons to move.

The electron movement is referred to as electricity. [1]

Electricity can be produced when electrons move from one element to another in a reaction known as redox or oxidation-reduction reaction.

Redox reaction means there’s a change in the oxidation status of one or more elements.

If a substance loses an electron, the oxidation increases, i.e., it’s oxidized.

If a substance gains an electron, the oxidation decreases, i.e., it’s reduced.

Electrochemistry is very important for biology and medicine as it can power cells in the body, which is why it’s tested on the MCAT.

Galvanic Cells

Alkaline battery background

Galvanic, also called voltaic cells, are devices that use a chemical reaction to create electricity.

This is the oxidation-reduction reaction.

One example of a galvanic cell is a battery. There are chemicals inside it, which react together in an oxidation-reduction reaction and make electricity.

Galvanic cells have a spontaneous reaction, and they always have a positive voltage.

A galvanic cell has two compartments that are called half-cells:

  • The anode is the half-cell where oxidation occurs.
  • The cathode is the half-cell where reduction occurs.

The anode is negative, while the cathode is positive, and it has a higher reduction potential.

“In order to tell which species will be reduced in a spontaneous situation, you need to look at the reduction potentials.” MCAT Self Prep YouTube Channel

The electrodes have to be connected so the electrons can flow.

They are connected with a salt bridge. The salt bridge is shaped like an upside-down U, and it has cotton plugs at the ends to prevent the solution from pouring out.

A salt bridge helps balance the charges in the half-cells to ensure they don’t build up too much, as that would prevent the galvanic cell from working.

The electrons in a galvanic cell flow from negative to positive electrode, i.e., from anode to cathode.

This creates an electrical current, so we can use electricity or a battery.

Here are the half-equations to know:

Anode (zinc electrode): Zn(s) Zn2+ (aq) +2e-

Cathode (copper electrode): Cu2+(aq)+2e-Cu (s)

Related Article: Physics Formulas for the MCAT

Cell Potential

The cell potential is calculated from half-cells potential.

To calculate the cell potential, the species oxidized and reduced have to be identified.

The difference in energy between the anode and cathode determines the movement of electrons.

They move from areas of higher energy to areas of lower energy.

If an anode has higher potential energy, electrons will move to the cathode.

The difference between the electrodes is measured in volts.

Electrolytic Cells

Electrolytic Cells visual diagram

I mentioned that voltaic cells use spontaneous chemical reactions to drive an electric current through an external circuit.

However, some cells work on a chemical system and drive an electric current through the system. These are electrolytic cells.

Like galvanic cells, electrolytic cells also have two half-cells, a reduction, oxidation half-cells, and it also requires a salt bridge.

The cathode and anode definitions stay the same. Reduction happens at the cathode and oxidation at the anode.

However, the flow of electrons in electrolytic cells is different. It can be reversed from spontaneous electron flow.

Since both half-reactions have been reversed, the sign of the cell potential is reversed, not the magnitude, which was the case in galvanic cells.

Galvanic Vs. Electrolytic Cell Differences

Here are the differences between galvanic and electrolytic cells:

Galvanic Cell Electrolytic Cell
The energy released by a spontaneous redox reaction is converted to electrical energy. The electrolytic energy drives a nonspontaneous redox reaction. Electrical energy is converted into chemical.
Half-cells are in different containers, connected with a salt bridge. Two electrodes are in the same container.
Anode is negative, cathode is positive. Anode is positive, cathode is negative.
Electrons go from anode to cathode in an external circuit. Electrons go from cathode to anode and are provided by an external battery.
Overall cell reaction:

Y+ZY++Z-(G<0)

Overall cell reaction:

Y++Z-Y+Z (G>0)

Galvanic Vs. Electrolytic Cell: Final Thoughts

Although electrochemistry isn’t one of the highest-yielding areas on the MCAT, it’s still worth paying some attention to.

Electrochemistry is important for body functions, so expect you’ll get some questions in this area as well.

Take your time, and go through galvanic and electrolytic cell definitions. Make sure you understand how they are similar and where they differ.

Then, try to do some practice tests until you are confident you understand this issue.


References:

  1. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules

About the author

Add Comment

Click here to post a comment