The key difference between galvanic cell and concentration cell is that a galvanic cell may or may not have the two half cells with the same composition whereas a concentration cell has two half cells with the same composition.
Both the galvanic cell and the concentration cell are electrochemical cells. An electrochemical cell is a device that can generate electricity using a chemical reaction or make a chemical reaction occur using electricity.
CONTENTS
1. Overview and Key Difference
2. What is Galvanic Cell
3. What is Concentration Cell
4. Side by Side Comparison – Galvanic Cell vs Concentration Cell in Tabular Form
5. Summary
What is a Galvanic Cell?
A galvanic cell is a type of electrochemical cell that uses spontaneous redox reactions to generate electrical energy. A synonym for this cell is voltaic cell. The cell contains two half cells that can be either of the same composition or of different compositions. Each half cell contains an electrode and an electrolyte. The electrode should be immersed in the electrolytic solution. Sometimes these electrolytes are completely separate, but other times they are separated only by a porous barrier. When the electrolytes are completely separated, we need to use a salt bridge to maintain the movement of ions between the two electrolytes.
Figure 01: Simple Galvanic Cell
In preparing this cell, we need to consider whether the electrodes and electrolytes are spontaneous or not. We can find it theoretically by calculating the electrode potentials of each half cell. However, one-half cell should show oxidation, whereas the other half cell should show a reduction reaction. Oxidation occurs at the anode, whereas reduction occurs at the cathode. Since a galvanic (voltaic) cell uses the energy released during a spontaneous redox reaction to generate electricity, galvanic cells are important as a source of electrical energy. They produce direct current.
What is a Concentration Cell?
Concentration cell is a type of galvanic cell in which the two half cells of the cell are similar in composition. Therefore, we say the two half cells are equivalent. They only differ in concentration. The voltage produced by this cell is very small since this cell tends to obtain an equilibrium state. The equilibrium comes when the concentrations of the two half cells become equal.
The concentration cell produces electricity via reduction of thermodynamic free energy of the system. Since the composition of the half cells is similar, the same reaction occurs, but in opposite directions. This process increases the concentration of the lower concentration cell and decreases the concentration of the higher concentration cell. As the electricity flows, thermal energy is generated. The cell absorbs this energy as heat. There are two types of concentration cells as follows:
- Electrolyte concentration cell – the electrodes are made up of the same substance, and the half cells contain the same electrolyte with different concentrations
- Electrode concentration cell – two electrodes (of the same substance) of different concentrations are dipped in the same electrolyte
What is the Difference Between Galvanic Cell and Concentration Cell?
A galvanic cell is a type of electrochemical cell that uses spontaneous redox reactions to generate electrical energy. A concentration cell, on the other hand, is a type of galvanic cell in which the two half cells of the cell are similar in composition. Therefore, the key difference between galvanic cell and concentration cell is that galvanic cell may or may not have the two half cells with the same composition whereas concentration cell has two half cells with the same composition.
Moreover, the electrodes of galvanic cell can be made of either the same substance or different substances while the electrodes of concentration cell are made of the same substance with either the same concentration or different concentrations. In addition to these, galvanic cells have the same electrolyte or different electrolytes in two half cells while concentration cells have the same electrolyte with either the same concentration or different concentrations.
The below infographic summarizes the difference between galvanic cell and concentration cell.
Summary – Galvanic Cell vs Concentration Cell
A galvanic cell is a type of electrochemical cell that uses spontaneous redox reactions to generate electrical energy. Concentration cell is a type of galvanic cell in which the two half cells of the cell are similar in composition. Therefore, the key difference between galvanic cell and concentration cell is that galvanic cell may or may not have the two half cells with the same composition whereas concentration cell has two half cells with the same composition.
Reference:
1. Helmenstine, Anne Marie. “Electrochemical Cells.” ThoughtCo, Jan. 26, 2019, Available here.
Image Courtesy:
1. “Galvanic Cell” By Gringer – File:Galvanische Zelle.png, by Tinux (CC BY-SA 3.0) via Commons Wikimedia