The key difference between concentration cell and chemical cell is that, in concentration cells, the compositions of two half cells are similar whereas, in the chemical cells, the compositions may or may not similar.
Concentration cell is a type of electrochemical cell. There are two types of electrochemical cells or chemical cells as galvanic cells and electrolytic cells. The concentration cell is a type of galvanic cell.
CONTENTS
1. Overview and Key Difference
2. What is a Concentration Cell
3. What is a Chemical Cell
4. Side by Side Comparison – Concentration Cell vs Chemical Cell in Tabular Form
5. Summary
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 the 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. So, 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 a Chemical Cell
A chemical cell, more precisely an electrochemical cell, is a system (a device) that can produce electrical energy through spontaneous chemical reactions. The chemical reactions that are involved in this process are called redox reactions. These reactions occur through the transferring of electrons between chemical species. Moreover, a redox reaction has two half-reactions known as oxidation reaction and reduction reaction. While oxidation reactions always release electrons to the system, reduction reactions take electrons from the system. Thus, we can say that the two half-reactions occur simultaneously.
There are two types of electrochemical cells as voltaic (galvanic) cells and electrolytic cells. An electrochemical cell is composed of two half cells. The half-reactions occur in these two half cells. Moreover, the chemical reactions that take place in a cell cause the build-up of a potential difference between two half cells.
Figure 01: A Simple Galvanic Cell
A half-cell generally consists of an electrode and an electrolyte. Therefore, a complete electrochemical cell has two electrodes and two electrolytes; the two half cells may sometimes use the same electrolyte. If there are two different electrolytes, then a salt bridge is used to maintain contact between the electrolytes. And, this is done by making a passage to transfer ions through the salt bridge. The electrons flow from one-half cell to the other through an external circuit. We call these two electrodes anode and cathode.
Moreover, oxidation and reduction reactions occur in two electrodes separately. While the oxidation reaction occurs in the anode, the reduction reaction occurs in the cathode. Therefore, electrons are produced in the anode and they move from the anode to the cathode through the external circuit. The salt bridge helps to maintain the system neutral (electrically) by transferring ions through it in order to balance the electrical charges.
What is the Difference Between Concentration Cell and Chemical Cell?
Concentration cell is a type of electrochemical cell. There are two types of chemical cells; they are the galvanic cells and electrolytic cells. The concentration cell is a type of galvanic cell. The key difference between concentration cell and chemical cell is that in concentration cells, the composition of two half cells is similar whereas, in chemical cells, the compositions may or may not be similar.
Below is a summary of the difference between concentration cell and chemical cell.
Summary – Concentration Cell vs Chemical Cell
Concentration cell is a type of electrochemical cell. There are two types of chemical (electrochemical) cell can as galvanic cells and electrolytic cells. To be precise, a concentration cell is a type of galvanic cell. The key difference between concentration cell and chemical cell is that in concentration cells the composition of two half cells is similar whereas in chemical cells the compositions may or may not similar.
Reference:
1. Narendra Sriramula. “Chemical Cell.” Slideshare.net. Available here.
Image Courtesy:
1. “Cell 3” By 473SHRUTHI V – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Galvanic Cell” By Gringer – File:Galvanische Zelle.png, by Tinux (CC BY-SA 3.0) via Commons Wikimedia