Electricity from Redox Reactions: Galvanic Cells Study Notes

Definition: Electrochemistry involves the production of electric current from a chemical reaction known as a redox reaction. It also includes the opposite process where an electric current is used to produce a chemical change; this is referred to as an electrolytic cell.
- Redox Reaction: A reaction that involves both reduction and oxidation processes occurring simultaneously.
Flow of Electrons: In electrochemistry, the reduction and oxidation half-reactions occur at different locations and can be connected by a wire, allowing electrons to flow from one location to another.
Galvanic Cell: A device that generates electric current from redox reactions occurring in two half-cells connected by an external circuit.

Definition: A half cell is a part of a galvanic cell where either reduction or oxidation reactions can occur, consisting of an electrode and an electrolyte.
- Equilibrium Setup: When a rod of metal (electrode) is dipped into a solution of its ions, an equilibrium is established between the metal and its ions.
- Potential Difference: The position of the equilibrium determines the potential difference between the metal strip and the metal ion solution.

Components of a Galvanic Cell: Two half cells connected to form a galvanic cell.
- Separation by Salt Bridge: The two half cells are separated by a salt bridge which typically contains a conducting solution like potassium nitrate (KNO₃).
- Connection via Electrode: The half cells are connected by a wire that facilitates the flow of electrons through electrodes, specifically designated as anode and cathode.
- Electron Flow direction: Electrons flow from the anode to the cathode.

Anode: (Negative Terminal)
- Role: Site of oxidation (where electrons are produced).
- Charge: Negative (-ve).
Cathode: (Positive Terminal)
- Role: Site of reduction (where electrons are accepted).
- Charge: Positive (+ve).
Mnemonic: "Anox and Redcat"
- Anode: Oxidation
- Cathode: Reduction.

Components:
- Anode: Zinc (Zn)
- Electrolyte: Copper Sulfate (CuSO₄)
- Cathode: Copper (Cu)

Oxidation Reaction at Anode:
- Equation: $ext{Zn}(s) <br>ightarrow ext{Zn}^{2+}(aq) + 2e^-$
- Description: Zinc solid dissolves as it is oxidized, producing electrons and zinc ions.
Reduction Reaction at Cathode:
- Equation: $ext{Cu}^{2+}(aq) + 2e^- <br>ightarrow ext{Cu}(s)$
- Description: Copper ions in solution gain electrons to form solid copper.

Complete Equation: $ext{Zn}(s) + ext{Cu}^{2+}(aq) <br>ightarrow ext{Zn}^{2+}(aq) + ext{Cu}(s)$

At the Anode: The zinc electrode progressively dissolves due to oxidation, converting solid zinc to zinc ions.
At the Cathode: The mass of the copper electrode increases as copper ions are reduced to the solid state.
Salt Bridge Function: Ions from the salt bridge migrate to maintain electrical neutrality; they balance the charges in the electrolytes around the electrodes.

Maintenance of Charge Balance: The salt bridge facilitates ion migration, restoring electrical neutrality in the galvanic cell.
- At Anode: Positive zinc ions ( ext{Zn}^{2+}) accumulate, prompting negative ions from the salt bridge to move toward the anode to balance positive charge.
- At Cathode: As copper ions reduce, negative charges from the electrolyte at the cathode create a deficit, requiring positive ions from the salt bridge to counteract this.

Depicts various galvanic cells demonstrating different metal electrodes immersed in electrolyte solutions containing respective metal ions.

Salt Bridge Composition: Typically KNO₃.
Electrodes: Metal electrodes are dipped in solutions containing the ion of the metal being used.
Inert Conductors: A galvanic cell can also use electrodes made of inert conductors (e.g., Pt or C) present in a solution with both oxidized and reduced forms of the element.

Gas Phase Electrodes: Structures can include gas (e.g., Cl₂) bubbling into a solution that contains oxidized or reduced forms of the gas. This configuration demonstrates the versatility of electrochemical systems in different scenarios.