Chemistry Lesson Note On Electrochemical Cells – Galvanic and Electrolytic Cells

Topic: Electrochemical Cells – Galvanic and Electrolytic Cells

Class: SS1

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Specific Objectives:

By the end of this lesson, students should be able to:

1. Define electrochemical cells.
2. Differentiate between galvanic (voltaic) and electrolytic cells.
3. Identify components and examples of each type of cell.
4. Describe the working principles of both galvanic and electrolytic cells.
5. Explain redox reactions in electrochemical cells.

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Instructional Materials:

• Diagrams of galvanic and electrolytic cells
• Voltmeter, wires, beakers, electrodes
• Electrolyte solutions (e.g., CuSO₄, ZnSO₄)
• Zinc and copper strips
• Salt bridge (e.g., filter paper soaked in KNO₃ solution)

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Lesson Content:

Step 1: Definition of Electrochemical Cells

An electrochemical cell is a system in which a redox (reduction-oxidation) reaction is used to produce or consume electrical energy.

There are two main types:

1. Galvanic (Voltaic) Cell – Produces electrical energy from spontaneous chemical reactions.
2. Electrolytic Cell – Uses electrical energy to drive non-spontaneous chemical reactions.

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Step 2: Galvanic (Voltaic) Cells

A galvanic cell converts chemical energy into electrical energy through redox reactions. It is the basis for batteries.

Example: Daniell Cell (Zn-Cu Cell)

Setup:

• Two half-cells:
  • Zn electrode in ZnSO₄ solution (anode)
  • Cu electrode in CuSO₄ solution (cathode)
• Salt bridge connects both solutions and allows ion flow
• Electrons flow from Zn to Cu through an external wire

Electrode Reactions:

• Anode (oxidation): Zn → Zn²⁺ + 2e⁻
• Cathode (reduction): Cu²⁺ + 2e⁻ → Cu

Direction of Current: From cathode to anode (external circuit)
Electron Flow: From anode (Zn) to cathode (Cu)

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Step 3: Electrolytic Cells

An electrolytic cell uses an external power source to drive a chemical change. It is the reverse of a galvanic cell.

Example: Electrolysis of Water (H₂O)

Setup:

• Electrodes placed in acidified water
• Power source (battery) connected
• Oxygen is released at the anode, hydrogen at the cathode

Electrode Reactions:

• Cathode (reduction): 2H⁺ + 2e⁻ → H₂
• Anode (oxidation): 2H₂O → O₂ + 4H⁺ + 4e⁻

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Step 4: Differences Between Galvanic and Electrolytic Cells

Feature	Galvanic Cell	Electrolytic Cell
Energy Conversion	Chemical → Electrical	Electrical → Chemical
Electron Flow	Anode → Cathode	Anode → Cathode
Anode	Negative	Positive
Cathode	Positive	Negative
Reaction	Spontaneous	Non-spontaneous
Example	Daniell cell	Electrolysis of water

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Step 5: Importance of Electrochemical Cells

• Galvanic cells are used in batteries (e.g., dry cells, car batteries).
• Electrolytic cells are used in electroplating, extraction of metals, and water splitting.

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Evaluation:

1. Define an electrochemical cell.
2. Differentiate between galvanic and electrolytic cells.
3. What are the electrode reactions in a Daniell cell?
4. In a galvanic cell, where does oxidation occur?
5. Mention two uses of electrolytic cells.

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Homework:

1. Draw and label a simple Daniell cell.
2. Explain how a salt bridge functions in a galvanic cell.
3. Why is the anode negative in a galvanic cell but positive in an electrolytic cell?

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Conclusion:

Electrochemical cells are fundamental in converting energy between chemical and electrical forms. Understanding how they work helps explain everyday devices like batteries and industrial processes like electrolysis.