Electrochemical power from spontaneous redox reactions — Daniell cell
& Nernst equation
E°cell (standard)
— V
Ecell (Nernst)
— V
Current I
— mA
Power P
— mW
ΔG° reaction
— kJ/mol
Reaction quotient Q
—
Electrochemistry & equations
Galvanic (voltaic) cell: converts chemical energy
of a spontaneous redox reaction directly into electrical energy.
Named after Alesandro Volta and Luigi Galvani.
Nernst equation: E = E° − (RT/nF)·ln(Q), where R =
8.314 J/mol·K, T = temperature, n = electrons transferred, F = 96485
C/mol, Q = [anode ions]/[cathode ions] for typical 2-electrode cell.
Gibbs free energy: ΔG = −nFE. For spontaneous
reaction, ΔG < 0 → E > 0.
Salt bridge / porous separator: allows ion
migration (Na⁺, K⁺, NO₃⁻) to maintain charge neutrality in each
half-cell without direct mixing of solutions.
About the Galvanic Cell Simulator
A galvanic (voltaic) cell converts the chemical energy of a spontaneous redox reaction directly into electrical energy. Two different metals are immersed in electrolyte solutions connected by a salt bridge; the less noble metal acts as the anode and oxidises, releasing electrons that flow through an external circuit to the cathode, where reduction occurs. The potential difference — the cell voltage — is determined by the standard reduction potentials of the two half-reactions.
The Nernst equation extends this picture to real conditions: E = E° − (RT/nF) ln Q, where Q is the reaction quotient of ion concentrations. As the cell discharges, Q rises toward the equilibrium constant K and the voltage falls to zero. Common galvanic pairs include zinc-copper (Daniell cell, ~1.1 V) and zinc-silver (~1.56 V); the electrochemical series ranks metals by their tendency to oxidise.
This simulator lets you choose metal pairs and ion concentrations, watch animated electron flow and ion migration, and see how the Nernst equation shifts the open-circuit voltage in real time. It is an ideal tool for understanding electrochemistry, battery chemistry, and corrosion.
Frequently Asked Questions
How does a galvanic cell produce electricity?
At the anode, a metal oxidises and releases electrons that travel through an external wire to the cathode, where they reduce ions in solution. This flow of electrons is an electric current. The two half-reactions are spatially separated so electrons must travel through the external circuit rather than transferring directly.
What is the Nernst equation?
E = E° − (RT/nF) ln Q, where E° is the standard potential, R the gas constant, T temperature in Kelvin, n the number of electrons transferred, F Faraday's constant, and Q the reaction quotient. It shows how cell voltage drops from its standard value as reactant concentrations decrease and product concentrations rise.
What does the salt bridge do?
It completes the ionic circuit by allowing counterions to migrate between half-cells, maintaining electrical neutrality in both compartments. Without a salt bridge, charge would accumulate and quickly stop the reaction. A saturated KCl or KNO₃ solution in an agar gel is common.
Why does the Daniell cell produce about 1.1 V?
The standard reduction potential of Cu²⁺/Cu is +0.34 V and of Zn²⁺/Zn is −0.76 V. The cell voltage is the cathode potential minus the anode potential: 0.34 − (−0.76) = 1.10 V under standard conditions (1 M solutions, 25 °C).
What is the difference between a galvanic cell and an electrolytic cell?
A galvanic cell generates electricity from a spontaneous redox reaction (negative ΔG). An electrolytic cell uses an external voltage to drive a non-spontaneous reaction (positive ΔG), such as electroplating or water splitting. Batteries are galvanic; chargers operate them as electrolytic cells.
About Galvanic Cell
A galvanic (voltaic) cell converts chemical energy from spontaneous redox reactions into electrical energy. It consists of two half-cells: an anode (where oxidation occurs, releasing electrons) and a cathode (where reduction occurs, consuming electrons). The classic Daniell cell uses a zinc anode in ZnSO₄ solution and a copper cathode in CuSO₄ solution, connected by a salt bridge that maintains electrical neutrality. Zinc oxidizes spontaneously (Zn to Zn2+ + 2e-) while copper ions are reduced at the cathode (Cu2+ + 2e- to Cu), with electrons flowing through the external circuit as measurable current.
The cell potential (EMF) is calculated from standard reduction potentials in the electrochemical series: E°cell = E°cathode minus E°anode. The Nernst equation corrects for non-standard concentrations: E = E° minus (RT/nF) times ln(Q), where Q is the reaction quotient, n is moles of electrons transferred, R is the gas constant, T is temperature, and F is Faraday's constant (96,485 C/mol). As the cell discharges, reactant concentrations change, Q approaches the equilibrium constant K, and the cell voltage decays toward zero at equilibrium.
This simulator lets you select anode and cathode materials from the electrochemical series, set ion concentrations, and observe the resulting cell voltage, spontaneous current direction, and how voltage changes as concentrations evolve over time. You can explore concentration cells (same electrodes, different concentrations), temperature effects on cell EMF, and the relationship between standard free energy change and cell potential: delta-G° = minus nFE°.
Frequently Asked Questions
What is the difference between a galvanic cell and an electrolytic cell?
A galvanic cell converts spontaneous chemical energy to electrical energy — the redox reaction is thermodynamically favorable (delta-G < 0) and drives current through an external circuit. An electrolytic cell does the opposite: it uses externally supplied electrical energy to force a non-spontaneous reaction (delta-G > 0). A rechargeable battery discharges as a galvanic cell and charges as an electrolytic cell using the same electrode reactions in reverse. The key distinction is directionality: galvanic cells release energy; electrolytic cells consume it.
What is a salt bridge and why is it necessary?
A salt bridge is a tube containing an electrolyte solution (often KCl in agar gel) connecting the two half-cells of a galvanic cell. As electrons flow through the external circuit from anode to cathode, positive ions accumulate at the cathode and negative ions accumulate at the anode, creating a charge imbalance that would quickly stop current flow. The salt bridge allows ions to migrate between half-cells — anions migrate toward the anode side, cations toward the cathode side — maintaining electrical neutrality without mixing the electrode solutions.
How does the Nernst equation affect cell voltage?
The Nernst equation E = E° minus (RT/nF) times ln(Q) shows that cell voltage depends on the concentrations of reactants and products. At standard conditions (all concentrations 1 M, 25°C, 1 atm gas), E = E°. When reactant concentrations are higher than standard or product concentrations are lower, Q < 1 and ln(Q) < 0, increasing the cell voltage above E°. As the cell discharges, reactants are consumed and products accumulate, increasing Q, decreasing E, until Q = K (equilibrium constant) and E = 0 — the cell is dead.
What determines whether a redox reaction is spontaneous?
A redox reaction is spontaneous when delta-G = minus nF times E_cell < 0, requiring E_cell > 0. This means the cathode reduction potential must exceed the anode reduction potential. A species higher in the electrochemical series (more positive reduction potential) will spontaneously oxidize a species lower in the series. For example, copper (E° = +0.34 V) spontaneously deposits from solution when zinc (E° = minus 0.76 V) is the anode, because E°cell = 0.34 minus (minus 0.76) = +1.10 V > 0.
How are galvanic cells used in practical batteries?
All batteries are galvanic cells optimized for specific applications. Alkaline batteries (zinc anode, MnO₂ cathode, KOH electrolyte) provide ~1.5 V with high energy density for everyday electronics. Lead-acid batteries (Pb anode, PbO₂ cathode, H₂SO₄ electrolyte) provide ~2 V per cell and deliver high current for automotive starting. Lithium-ion cells (graphite anode, LiCoO₂ or LiFePO₄ cathode, organic electrolyte) provide ~3.6 V with exceptional energy density for portable electronics and EVs. Fuel cells are galvanic cells that never deplete as long as fuel is supplied.