Galvanic cells and electrolysis – standard electrode potentials
ChemistryElectrochemistryAges 17–18Virtual lab
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Electrochemistry
Galvanic cell mode: two metal electrodes sit in solutions of their own salts, joined by a wire and a salt bridge; electrons flow through the wire from the anode (the metal with the lower E°, which is oxidized and dissolves) to the cathode (whose ions are reduced and deposit), and the voltmeter reads the standard cell potential E°cell = E°(+) − E°(−) from the standard electrode potential table. Electrolysis mode: a DC power source drives electrons to the cathode; ions migrate to the electrodes, producing Cu, H₂, O₂, Cl₂ or Na depending on the solution, and the product mass follows m = M·I·t/(n·F). The ΔG, K & Nernst view adds ΔG° = −nFE°cell and K = e^(nFE°/RT) for each cell, concentration sliders for both half-cells so that E follows the Nernst equation, a graph of E against log Q and a Cu–Cu concentration cell. The Decomposition voltage tab sweeps the voltage from 0 to 4 V, records the current–voltage curve, fits a straight line to find the decomposition voltage and compares it with the theoretical value from E°; the overpotential changes with the electrode (platinum, graphite) and the product.
Lesson: Standard electrode potentials, galvanic (voltaic) cells; electrolysis of solutions and molten salts; the Nernst equation and ΔG° = −nFE°; decomposition voltage and overpotential
What it shows
Two opposite processes are placed side by side. In a galvanic cell, a spontaneous redox reaction turns chemical energy into electrical energy: the metal with the lower standard electrode potential is oxidized, and the cell potential is the difference between the two E° values. The ΔG, K & Nernst view links E°cell to ΔG° = −nFE° and to the equilibrium constant K, and shows how E falls as the reaction quotient Q rises, reaching zero at equilibrium. Electrolysis works the other way, using electrical energy to drive a non-spontaneous reaction; the products depend on which species are most easily reduced and oxidized. The Decomposition voltage tab shows that almost no current flows until the voltage passes the theoretical value plus the overpotential, which is large for O₂ and for H₂ on graphite and small for deposited metals and Cl₂.
How to use
In Galvanic cell mode, go through the Electrode pair options and ask students to predict the voltmeter reading from the E° values. Press ΔG, K & Nernst, move the two concentration sliders, press Record point several times and check that the points lie on a line of gradient −0.0592/n; then try the Cu–Cu concentration cell. Press Switch to electrolysis, try each Electrolyte and change the Current to compare the mass of product. In the Decomposition voltage tab, choose a solution and an electrode, press Sweep 0–4 V, then Fit line, and compare the measured value with the theoretical one.
Parameters you can change
- Mode Galvanic cell, Electrolysis, Decomposition voltage
- Electrode pair (galvanic cell) Zn–Cu, Mg–Cu, Fe–Cu, Zn–Ag, Cu–Ag, Zn–Fe, Al–Cu, Cu–Cu (concentration cell)
- Electrolyte (electrolysis) CuSO₄ solution, inert electrodes, CuSO₄ solution, Cu anode (refining/plating), NaCl solution, with diaphragm, Molten NaCl
- Current 0.5–5 A
- Animation speed 0.5–3 ×
- Galvanic cell view Standard cell (E°), ΔG, K and Nernst equation
- Metal-ion concentration, left half-cell (Nernst) 0.0001–2 mol/L
- Metal-ion concentration, right half-cell (Nernst) 0.0001–2 mol/L
- Solution (decomposition voltage) HCl 1 mol/L, H₂SO₄, [H⁺] = 1 mol/L, CuSO₄ 1 mol/L, [H⁺] = 1 mol/L, ZnCl₂ 1 mol/L
- Electrode (decomposition voltage) Platinum, Graphite
- Applied voltage 0–4 V
Questions to explore
- Which electrode pair gives the largest cell potential, and how can you predict this from the standard electrode potentials?
- At the negative electrode of a galvanic cell, does oxidation or reduction take place, and what happens to its mass?
- Why is sodium produced when molten NaCl is electrolyzed, but not when NaCl solution is electrolyzed?
- For H₂SO₄ on platinum, how far above the theoretical value is the measured decomposition voltage, and what changes on graphite?
