Galvanic Cell
A galvanic cell (also called a voltaic cell) is an electrochemical device that converts chemical energy into electrical energy through spontaneous redox reactions occurring at two electrodes separated by an electrolyte. The oxidation half-reaction occurs at the anode (negative terminal) and the reduction half-reaction occurs at the cathode (positive terminal), with electrons flowing through an external circuit. Galvanic cells are the basis of all batteries and are fundamental to understanding energy storage and conversion in chemistry.
Key Formula
E_cell = E_cathode - E_anode
LaTeX: E_{cell} = E_{cathode} - E_{anode}
| Symbol | Meaning | Unit |
|---|---|---|
| E_{cell} | Cell electromotive force | V (volts) |
| E_{cathode} | Standard reduction potential of cathode | V |
| E_{anode} | Standard reduction potential of anode | V |
Worked Example
Problem
A galvanic cell is constructed using a zinc electrode in ZnSO₄ solution and a copper electrode in CuSO₄ solution. Given E°(Zn²⁺/Zn) = −0.76 V and E°(Cu²⁺/Cu) = +0.34 V, calculate the standard cell EMF.
Solution
Step 1: Identify anode and cathode. Zinc has a more negative reduction potential, so it is oxidised at the anode. Copper is reduced at the cathode. Step 2: Apply the cell EMF formula: E°_cell = E°_cathode − E°_anode Step 3: E°_cell = (+0.34 V) − (−0.76 V) = 0.34 + 0.76 = 1.10 V
Answer
E°_cell = 1.10 V
Comparison of Galvanic Cell Components
| Component | Electrode | Process | Charge | Example |
|---|---|---|---|---|
| Anode | Negative | Oxidation | Loses electrons | Zn → Zn²⁺ + 2e⁻ |
| Cathode | Positive | Reduction | Gains electrons | Cu²⁺ + 2e⁻ → Cu |
| Salt bridge | None | Ion transport | Maintains neutrality | KCl in agar |
| Electrolyte | None | Ion conduction | Conducts ions | CuSO₄, ZnSO₄ |
| External wire | None | Electron flow | Carries current | Copper wire |
Interactive Tools
PhET Electrochemistry Simulation
Interactive simulation for exploring galvanic cell voltage and electrode reactions
Open ToolKhan Academy – Galvanic Cells
Lessons and practice problems on galvanic cell design and EMF calculation
Open ToolWolfram Alpha Cell EMF Calculator
Compute cell potentials and explore electrochemical reactions
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Electrolytic Cell
An electrolytic cell is an electrochemical device that uses an external electrical energy source to drive non-spontaneous redox reactions, converting electrical energy into chemical energy. Unlike a galvanic cell, the anode is connected to the positive terminal of the power supply and the cathode to the negative terminal, and oxidation still occurs at the anode while reduction occurs at the cathode. Electrolytic cells are used industrially in processes such as electroplating, electro-refining of metals, chlor-alkali production, and the electrolysis of water.
Cell EMF
The electromotive force (EMF) of an electrochemical cell is the maximum potential difference between the two electrodes when no current is flowing (open-circuit condition), representing the driving force for electron transfer in the external circuit. It is determined by the difference in the electrode potentials of the cathode and anode and is directly related to the Gibbs free energy change of the reaction by ΔG° = −nFE°. A positive cell EMF indicates a spontaneous reaction (ΔG < 0), while a negative cell EMF indicates a non-spontaneous reaction under the given conditions.
Standard Electrode Potential
The standard electrode potential (E°) is the potential difference developed at an electrode when it is in contact with a 1 mol L⁻¹ solution of its ions at 25 °C (298 K) and 1 atm pressure, measured relative to the standard hydrogen electrode (SHE), which is assigned a potential of exactly 0.00 V. Positive values of E° indicate a greater tendency for reduction (the species is a stronger oxidising agent), while negative values indicate a tendency for oxidation. Standard electrode potentials are tabulated and used to predict the feasibility of redox reactions and to calculate cell EMFs.
Named after Italian physician Luigi Galvani (1737–1798), who discovered animal electricity through frog leg experiments. The term "voltaic cell" honours Alessandro Volta, who built the first true electrochemical cell around 1800.