Construction of cell and calculation of emf of the cell

Construction of Electrochemical Cell and Calculation of EMF

An electrochemical cell converts chemical energy into electrical energy through redox reactions. These cells are fundamental in batteries, fuel cells, and other energy conversion devices.

1. Construction of Electrochemical Cell

An electrochemical cell typically consists of two half-cells, each containing an electrode dipped in an electrolyte solution.

• Electrodes: Conductive materials (usually metals) that allow electron transfer. One functions as the anode (oxidation), and the other as the cathode (reduction).
• Electrolyte: A solution containing ions to complete the internal circuit by allowing ionic movement.
• Salt Bridge: A U-shaped tube filled with an inert electrolyte (e.g., KCl or KNO₃) that maintains electrical neutrality by allowing ion exchange between the two half-cells.
• External Circuit: A wire connecting the electrodes through which electrons flow from the anode to the cathode.

2. Representation of Cell

Cell representation is done using a symbolic notation, where the anode and cathode half-cells are written with a double vertical line in between, indicating the presence of a salt bridge:

Example: Zn | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu

This represents a Daniell cell in which zinc serves as the anode and copper functions as the cathode.

3. Calculation of EMF of the Cell

The cell potential, also known as electromotive force (EMF), refers to the voltage difference between the two electrodes. It is calculated using the standard electrode potentials (E°) of the half-cells:

Formula:

E_cell^° = E_cathode^° – E_anode^°

• If E_cell° is positive, the reaction is spontaneous under standard conditions.
• Standard conditions include 1 M concentration, 1 atm pressure, and 25°C temperature.

Example Calculation

For a Daniell cell:

• E_cathode° (Cu²⁺/Cu) = +0.34 V
• E_anode° (Zn²⁺/Zn) = –0.76 V

E_cell° = 0.34 – (–0.76) = 1.10 V

Applications

• Used in batteries and portable energy sources.
• Helpful in understanding redox processes and reaction feasibility.
• Used in determining standard electrode potentials experimentally.