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71 Using Electrochemistry to Generate Electricity
71 Using Electrochemistry to Generate Electricity
LumenLearning
Dry Cell Battery
A dry-cell battery uses an immobilized electrolyte that minimizes moisture and allows for superior portability.
LEARNING OBJECTIVES
Discuss the operational components of a dry cell battery and their principal benefits
KEY TAKEAWAYS
Key Points
- A battery contains electrochemical cells that can store chemical energy to be converted to electrical energy.
- A dry-cell battery stores energy in an immobilized electrolyte paste, which minimizes the need for water.
- Common examples of dry-cell batteries include zinc-carbon batteries and alkaline batteries.
Key Terms
Defining a Dry Cell
In electricity, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. The dry cell is one of many general types of electrochemical cells.
A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Unlike a wet cell, a dry cell can operate in any orientation without spilling, as it contains no free liquid. This versatility makes it suitable for portable equipment. By comparison, the first wet-cell batteries were typically fragile glass containers with lead rods hanging from an open top. They, therefore, needed careful handling to avoid spillage. The development of the dry-cell battery allowed for a major advance in battery safety and portability.
A common dry-cell battery is the zinc-carbon battery, which uses a cell that is sometimes called the Leclanché cell. The cell is made up of an outer zinc container, which acts as the anode. The cathode is a central carbon rod, surrounded by a mixture of carbon and manganese(IV) dioxide ([latex]\text{MnO}_2[/latex]). The electrolyte is a paste of ammonium chloride ([latex]\text{NH}_4\text{Cl}[/latex]). A fibrous fabric separates the two electrodes, and a brass pin in the center of the cell conducts electricity to the outside circuit.
Chemical reactions occur in every part of the battery to allow for energy storage; the reactions can be described using balanced chemical equations that delineate the electron flow. The paste of ammonium chloride reacts according to the following half-reaction:
[latex]\text{2NH}_4 (aq) + \text{2e}^- \rightarrow \text{2NH}_3 (g) + \text{H}_2 (g)[/latex]
The manganese(IV) oxide in the cell removes the hydrogen produced by the ammonium chloride, according to the following reaction:
[latex]\text{2MnO}_2 (s) + \text{H}_2 (g) \rightarrow \text{Mn}_2\text{O}_3 (s) + \text{H}_2\text{O} (l)[/latex]
The combined result of these two reactions takes place at the cathode. Adding these two reactions together, we get:
[latex]\text{2NH}_4 (aq) + \text{2MnO}_2 (s) + \text{2e}^- \rightarrow \text{Mn}_2\text{O}_3 (s) + \text{2NH}_3 (g) + \text{H}_2\text{O} [/latex]
Finally, the anode half-reaction is as follows:
[latex]\text{Zn} (s) \rightarrow \text{Zn}^{2+} + \text{2e}^-[/latex]
Therefore, the overall equation