A galvanic cell and an electrolytic cell are two types of electrochemical cells that operate based on the principles of redox reactions. A galvanic cell, also known as a voltaic cell, converts chemical energy into electrical energy through a spontaneous chemical reaction. It consists of two electrodes (anode and cathode) immersed in an electrolyte, where the anode is negatively charged and the cathode is positively charged. In contrast, an electrolytic cell uses electrical energy from an external source to drive a non-spontaneous chemical reaction. Here, the anode is positively charged, and the cathode is negatively charged. Galvanic cells are commonly used in batteries, while electrolytic cells are used in processes like electroplating and electrolysis.
Key Points Explained:
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Definition and Purpose:
- Galvanic Cell: Converts chemical energy into electrical energy through a spontaneous redox reaction. It is a source of electrical energy.
- Electrolytic Cell: Converts electrical energy into chemical energy by driving a non-spontaneous redox reaction. It requires an external power source.
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Energy Conversion:
- Galvanic Cell: Chemical energy → Electrical energy (spontaneous process).
- Electrolytic Cell: Electrical energy → Chemical energy (non-spontaneous process).
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Electrode Charges:
- Galvanic Cell: Anode is negatively charged, and cathode is positively charged.
- Electrolytic Cell: Anode is positively charged, and cathode is negatively charged.
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Reaction Spontaneity:
- Galvanic Cell: The reaction is spontaneous, with a negative Gibbs free energy (ΔG < 0).
- Electrolytic Cell: The reaction is non-spontaneous, with a positive Gibbs free energy (ΔG > 0).
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Applications:
- Galvanic Cell: Used in batteries, such as alkaline batteries and lithium-ion batteries, to provide portable power.
- Electrolytic Cell: Used in processes like electroplating, electrolysis of water, and recharging rechargeable batteries.
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Electrolyte and Electrodes:
- Both cells consist of two electrodes (anode and cathode) immersed in an electrolyte solution.
- In a galvanic cell, the electrolyte facilitates the flow of ions to maintain charge balance during the redox reaction.
- In an electrolytic cell, the electrolyte provides the medium for ion migration under the influence of an external voltage.
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Rechargeability:
- Galvanic Cell: Can be rechargeable (e.g., lithium-ion batteries) or non-rechargeable (e.g., single-use alkaline batteries).
- Electrolytic Cell: Typically not rechargeable; it consumes energy to drive chemical reactions.
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Discharge Potential:
- Electrolytic Cell: Requires a minimum potential (discharge potential) to initiate electrolysis and discharge ions at the electrodes.
- Galvanic Cell: Generates its own potential difference due to the spontaneous redox reaction.
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Ion Liberation:
- In an electrolytic cell, cations (positive ions) are liberated at the cathode, and anions (negative ions) are liberated at the anode.
- If multiple ions are present, the ion with the higher reduction potential is liberated at the cathode, and the ion with the lower reduction potential is liberated at the anode.
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Equilibrium in Electrochemical Cells:
- An electrochemical cell in equilibrium lies between a galvanic and electrolytic cell, with no current flow when the counter electromotive force balances the reaction.
By understanding these key points, one can differentiate between galvanic and electrolytic cells and appreciate their distinct roles in energy conversion and chemical processes.
Summary Table:
| Aspect | Galvanic Cell | Electrolytic Cell |
|---|---|---|
| Definition | Converts chemical energy into electrical energy (spontaneous redox reaction). | Converts electrical energy into chemical energy (non-spontaneous redox reaction). |
| Energy Conversion | Chemical → Electrical (spontaneous). | Electrical → Chemical (non-spontaneous). |
| Electrode Charges | Anode: Negative, Cathode: Positive. | Anode: Positive, Cathode: Negative. |
| Reaction Spontaneity | Spontaneous (ΔG < 0). | Non-spontaneous (ΔG > 0). |
| Applications | Batteries (e.g., alkaline, lithium-ion). | Electroplating, electrolysis, recharging batteries. |
| Rechargeability | Can be rechargeable or non-rechargeable. | Typically not rechargeable. |
| Discharge Potential | Generates its own potential difference. | Requires external voltage to initiate electrolysis. |
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