Electrochemistry is the field of chemistry that deals with the relationship between electrical energy and chemical reactions. Half cell and complete cell are two common terms in the field of electrochemistry to discuss redox reactions.
What is the difference between half cell and complete cell? A half-cell is a single electrode immersed in a solution containing its ions, whereas a complete cell is a combination of two half cells connected by a salt bridge or a porous barrier.
Key Areas Covered
1. What is a Half Cell
– Definition, Features
2. What is a Complete Cell
– Definition, Features
3. Similarities Between Half Cell and Complete Cell
– Outline of Common Features
4. Difference Between Half Cell and Complete Cell
– Comparison of Key Differences
5. FAQ: Half Cell and Complete Cell
– Answers to Frequently Asked Questions
Key Terms
Half Cell, Complete Cell, Electrochemical Cell
What is a Half Cell
A half cell consists of a metal electrode immersed in a solution containing its ions. This cell has few components. They are the electrode, salt bridge, and solution. A solid conductor, such as a metal or a nonmetal, acts as the electrode. The electrode can either be an anode or a cathode. This depends on what happens in it when it participates in the redox reaction. The solution is a liquid containing ions of the metal or nonmetal used in the electrode. Ions migrate and participate in the redox reaction, where the solution acts as the medium. Moreover, the salt bridge connects the two half cells together in an electrochemical cell. Ions flow through this, thus preventing the mixing up of solutions.
Near a half cell, a reduction reaction or an oxidation reaction happens. In a reduction reaction, the gaining of electrons occurs. However, in an oxidation reaction, the loss of electrons happens mostly by metal atoms.
The example of a half-reaction is given below.
A copper half cell consists of a copper electrode immersed in a solution containing copper ions (Cu²⁺). The formation of copper atoms by gaining electrons by copper ions (reduction) is seen near the electrode. Here, the copper atoms deposit on the surface of the electrode.
The half-reaction can be written as: Cu²⁺(aq) + 2e⁻ → Cu(s)
Furthermore, there are two main types of half cells: metal-metal ion half cells and electrode half cells.
What is a Complete Cell
A complete cell is a unit consisting of two half cells connected by a salt bridge or porous barrier. This unit is frequently found in electrochemistry. Here, chemical energy is converted into electrical energy and vice versa. At the two half cells, they undergo a redox reaction. At each half cell, either an oxidation reaction or a reduction reaction happens. When two half cells are connected by a conductor, electrons can move through it. This flow of current is called an electric current.
The electrical neutrality of the cell is achieved by the porous barrier or the salt bridge. This facilitates the flow of ions. The choice of electrodes and electrolytes depends on the redox reaction that is being studied.
There are two types of electrochemical cells: galvanic cells and electrolytic cells. Galvanic cells convert chemical energy into electrical energy. Electrolytic cells convert electrical energy into chemical energy. In a galvanic cell, the redox reaction is spontaneous, while in an electrolytic cell, the redox reaction is nonspontaneous. Batteries and fuel cells are examples of galvanic cells, while examples of electrolytic cells include the electrolysis of water to produce hydrogen and oxygen and the refining of metals.
Complete cells have many uses. They are used in fuel cells, sensors, electroanalysis, electrorefining, electroplating, corrosion protection, as well as in batteries.
Similarities Between Half Cell and Complete Cell
- Half cells and complete cells contain electrodes.
- Both cells require electrolytes.
- Moreover, both cells involve redox reactions.
- Additionally, these types of cells can generate a potential difference.
Difference Between Half Cell and Complete Cell
Definition
- A half-cell is a single electrode immersed in a solution containing its ions, whereas a complete cell is a combination of two half cells connected by a salt bridge or a porous barrier.
Redox Reaction
- Half cells exhibit only one half of a redox reaction (either oxidation or reduction), whereas complete cells undergo a complete redox reaction involving both oxidation and reduction.
Voltage
- A half cell does not produce a measurable voltage on its own, while a complete cell generates a measurable voltage due to the potential difference between the two half cells.
Existence
- Half cells exist independently, while complete cells require connection to another half cell to function.
Conclusion
Two half cells together make up a complete cell. Redox reactions are seen occurring in half cells and complete cells. The main difference between half cell and complete cell is that half cell contains a single electrode immersed in a solution of its corresponding ions while complete cell contains two half cells connected by a salt bridge or porous barrier. There are many applications of half cells and complete cells in the field of electrochemistry.
FAQ: Half Cell and Complete Cell
1. What are the two types of cells in electrochemistry?
The two types of cells in electrochemistry are:
- Galvanic cells: Convert chemical energy into electrical energy.
- Electrolytic cells: Convert electrical energy into chemical energy.
2. What is half cell reaction in electrochemistry?
A half cell reaction is a chemical reaction that occurs at one electrode in an electrochemical cell. It involves either the oxidation (loss of electrons) or reduction (gain of electrons) of a chemical species.
3. What is half cell potential in electrochemistry?
Half-cell potentials are the voltages measured between a metal electrode and a solution containing its ions. In fact, they represent the tendency of a metal to lose or gain electrons.
4. Can we construct an electrochemical cell with two half-cells?
Yes, you can construct an electrochemical cell with two half-cells. Each half-cell contains a metal electrode immersed in a solution of its ions. When connected, a redox reaction occurs, generating electrical energy.
5. Is a cathode a half-cell?
Yes, a cathode is a half-cell. A half-cell is a component of an electrochemical cell where oxidation or reduction occurs. The cathode is the half-cell where reduction takes place.
Reference:
1. “Half-Cell Reaction.” LibreText Chemistry.
2. “Electrochemical Cell.” Science Direct.
Image Courtesy:
1. “Galvanic cell with no cation flow” By Original: Ohiostandard Vector: AntiCompositeNumber – Own work(CC BY-SA 4.0) via Commons Wikimedia
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