Electrochemical Cells and Electrode Potential — Part 1: Cells and the standard hydrogen electrode: visual lesson, ISC Class 12 Chemistry

Lesson

Electrochemical cells

Part 1 — turning a redox reaction into an electric current, and measuring electrode potentials.

In this lesson you will

Compare electrolytic and electrochemical (galvanic) cells
Explain how a Daniell cell produces a current and write its half-reactions and cell notation
Describe the standard hydrogen electrode, its preparation, use and limitations
Explain how the standard electrode potentials of Zn²⁺/Zn and Cu²⁺/Cu are measured against the SHE

Concept

Electrolytic and electrochemical cells

In an electrochemical (galvanic or voltaic) cell, a spontaneous redox reaction produces electrical energy. In an electrolytic cell, electrical energy from an outside source drives a non-spontaneous reaction. In both, oxidation occurs at the anode and reduction at the cathode.

Table comparing electrochemical and electrolytic cells
Feature	Electrochemical (galvanic) cell	Electrolytic cell
Energy change	Chemical → electrical	Electrical → chemical
Reaction	Spontaneous (ΔG < 0)	Non-spontaneous, driven by a battery
Anode sign	Negative	Positive
Cathode sign	Positive	Negative
Salt bridge	Usually needed	Not needed (one vessel)
Example	Daniell cell, dry cell	Electroplating, electrolysis of brine

Diagram

The Daniell cell

Zinc is the anode (oxidation, negative); copper is the cathode (reduction, positive).

A zinc rod in ZnSO₄ solution and a copper rod in CuSO₄ solution, joined by a wire and a salt bridge. With 1 M solutions at 298 K the voltmeter reads about 1.10 V.

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