Voltaic (Galvanic) cells

1. Definition

• A Galvanic (Voltaic) cell is an electrochemical cell that converts chemical energy into electrical energy through a spontaneous redox reaction.
• Used in batteries (e.g., standard AA cells) to generate electricity.

2. Structure of a Galvanic Cell

A Galvanic cell consists of:

1. Two half-cells, each containing an electrode in an electrolyte.
2. A salt bridge, which allows ion flow to maintain charge balance.
3. An external circuit, where electrons move from the anode to the cathode.

3. Example: Zinc-Copper $(Zn-Cu)$ Galvanic Cell

Electrode Reactions

• At the anode (oxidation): $Zn(s) \rightarrow Zn^{2+}(aq) + 2e^-$

• At the cathode (reduction): $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$

• Overall cell reaction: $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$

4. Functions of Key Components

a) Anode and Cathode

• Anode (negative electrode):
  • Oxidation occurs ($Zn$ loses electrons).
  • $Zn$ dissolves into the solution as Zn²⁺ ions.
• Cathode (positive electrode):
  • Reduction occurs ($Cu²⁺$ gains electrons).
  • Solid $Cu$ metal deposits onto the electrode.

b) Salt Bridge

• Contains an electrolyte solution (e.g., $KNO₃$ or $KCl$).
• Allows ion movement to maintain charge balance.
• Prevents direct mixing of solutions, which would stop the reaction.

c) Electrolyte Solutions

• Zinc half-cell: $ZnSO_4$ solution (contains $Zn^{2+}$ ions).
• Copper half-cell: $CuSO_4$ solution (contains $Cu^{2+}$ ions).

d) Electron Flow

• Electrons flow from the anode $(Zn)$ to the cathode $(Cu)$ through the external circuit.
• This flow generates electricity.

5. Key Features of a Galvanic Cell

Feature	Galvanic Cell
Energy Conversion	$Chemical → Electrical$
Reaction Type	Spontaneous
Electrode Charges	$Anode = Negative, Cathode = Positive$
Electron Flow	From anode to cathode
Salt Bridge	Maintains charge balance
Example	$Zn-Cu$ cell

6. Key Takeaways

• Anode undergoes oxidation, and cathode undergoes reduction.
• Electrons flow from anode (negative) to cathode (positive).
• Galvanic cells generate electrical energy from a spontaneous redox reaction.
• The salt bridge maintains charge neutrality and completes the circuit.