Electrochemical Cell Voltage Calculator
Calculate the standard cell potential (E°cell) for any electrochemical cell from standard electrode potentials. Determine spontaneity and write cell notation.
Electrochemical Cells Guide
Cell Potential Calculation
E°cell = E°cathode − E°anode. The cathode is the electrode where reduction occurs (gains electrons); the anode is where oxidation occurs (loses electrons). By convention, standard electrode potentials are all written as reduction potentials. The more positive the reduction potential, the stronger the oxidising agent. Example: zinc-copper cell. Cathode (Cu²⁺/Cu): +0.34 V. Anode (Zn²⁺/Zn): −0.76 V. E°cell = 0.34 − (−0.76) = +1.10 V. A positive E°cell means the reaction is spontaneous in the forwar
Gibbs Free Energy and Spontaneity
ΔG° = −nFE°cell. Where n = moles of electrons transferred, F = Faraday's constant (96,485 C/mol), E°cell = standard cell potential. If E°cell > 0: ΔG° < 0 → spontaneous. If E°cell < 0: ΔG° > 0 → non-spontaneous (would require external energy — electrolysis). If E°cell = 0: ΔG° = 0 → equilibrium. For the zinc-copper cell (n=2): ΔG° = −2 × 96485 × 1.10 = −212 kJ/mol. Relationship to equilibrium: ΔG° = −RT ln K, so ln K = nFE°/RT = nE°/0.02569 at 298 K.
The Electrochemical Series
The electrochemical series lists half-cells in order of standard electrode potential, from most negative (strongest reducing agents: Li, K, Na, Mg, Al) to most positive (strongest oxidising agents: F₂, MnO₄⁻, O₂, Cl₂). Rules: a more positive half-cell always oxidises a more negative one. Displacement reactions: zinc displaces copper from copper sulfate solution because Zn has a more negative E° (−0.76 V) than Cu (+0.34 V). Electroplating: the metal to be deposited is the cathode in an electrolyt
Real Cells vs Standard Conditions
Standard electrode potentials apply at 298 K, 1 mol/L concentrations, and 1 atm for gases. Real cells deviate due to concentration effects (Nernst equation): E = E° − (RT/nF) × ln Q. At 298 K: E = E° − (0.0257/n) × ln Q. This is important for: batteries as they discharge (reactant concentrations decrease), pH cells (glass electrode measures H⁺ concentration), and biological systems where concentrations are far from 1 mol/L. The Daniell cell (Zn/Cu) in everyday conditions operates at approximatel
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