Galvanic Cell and Electrolysis Simulator
Equations in this simulation
| E° | standard electrode potential | measured against hydrogen at 1 mol/L and 25 °C; the metal with the lower E° gives up electrons and is the anode | |
|---|---|---|---|
| E°cell | standard cell potential | the voltage with both solutions at 1 mol/L; positive means the cell runs by itself |
With the current values:
| n | electrons transferred | 2 for zinc and copper | |
|---|---|---|---|
| F | Faraday constant | 96,485 C per mole of electrons | |
| Q | reaction quotient | [ion at the anode] ÷ [ion at the cathode], each to the power of its share of n; as the cell runs Q rises and E falls, until the cell is flat | |
| E | cell potential now | what the voltmeter reads with no current drawn |
With the current values:
| ΔG | Gibbs energy of the cell reaction | negative for a cell that runs by itself; −212 kJ/mol for the Daniell cell |
|---|
With the current values:
| I | current | r = 5 Ω is the cell's own resistance | |
|---|---|---|---|
| moles | metal dissolved or plated | Faraday's law: each mole of a 2+ ion needs two moles of electrons |
With the current values:
| Q | charge passed | I × t; the supply must give at least 1.23 V, plus about 0.6 V more to push the reactions along | |
|---|---|---|---|
| V | volume of each gas | at 25 °C and 1 atm, 24.5 L per mole: twice as much hydrogen as oxygen |
With the current values:
How to use the galvanic cell and electrolysis simulator
- In a galvanic cell, choose a metal for each side, each standing in a solution of its own ions, joined by a wire and a salt bridge. The metal with the lower standard potential is the anode: it dissolves, giving up electrons that run through the wire to the other electrode, where metal ions take them and plate out. The meter shows the cell potential.
- Change the concentrations to see the Nernst equation shift the voltage, and lower the load resistance to draw more current. Run the cell and watch the anode thin, the cathode thicken and, with copper, the blue solution fade, while the voltage slowly falls; the charts follow it. The Nernst Equation Calculator works out the potential of a half-cell at any concentration.
- Switch to electrolysis of water and set the supply voltage. Above about 1.8 V the current splits water: hydrogen collects over the negative electrode and oxygen over the positive one, twice as much hydrogen, as Faraday's laws predict from the charge passed.
Frequently asked questions
How does a galvanic cell make electricity?
Two metals hold on to their electrons with different strength, measured by their standard electrode potentials. Zinc (−0.76 V) gives its electrons up more readily than copper (+0.34 V), so in the Daniell cell zinc atoms dissolve as Zn²⁺, the electrons flow through the wire, and Cu²⁺ ions take them at the copper electrode. The salt bridge lets ions move between the beakers to keep both solutions neutral; without it the current stops at once.
How do I work out the cell potential?
E°cell = E°cathode − E°anode with both solutions at 1 mol/L: 0.34 − (−0.76) = 1.10 V for zinc and copper. At other concentrations the Nernst equation corrects it: E = E° − (RT ÷ nF) ln Q, where Q = [Zn²⁺] ÷ [Cu²⁺]. Ten times more zinc ions than copper ions lowers the voltage by about 30 mV.
What is Faraday's law of electrolysis?
The amount of substance made or used at an electrode is proportional to the charge passed: moles = Q ÷ (zF), where Q = I × t, z is the number of electrons per ion and F = 96,485 C/mol. Splitting water needs 2 electrons per hydrogen molecule and 4 per oxygen molecule, which is why exactly twice as much hydrogen collects.
Why does electrolysis of water need more than 1.23 V?
1.23 V is the thermodynamic minimum, the cell potential of the reaction run backward. In practice the electrode reactions need an extra push, the overpotential, and the solution has resistance, so real cells run at 1.8 to 2.5 V. Pure water barely conducts, so an electrolyte such as sodium sulfate is added; it carries the current without being used up.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.