Electrochemistry Cell Potential

This calculator builds a galvanic cell from two standard reduction potentials: E°cell = E°cathode − E°anode, where both half-reaction potentials are entered as reduction potentials (never flip the anode's sign yourself — the subtraction already handles the fact that the anode undergoes oxidation). With the default zinc-copper cell (cathode Cu²⁺/Cu at +0.34 V, anode Zn²⁺/Zn at −0.76 V), that gives the classic 1.10 V standard cell potential. From there it applies the Nernst equation, E = E° − (RT/nF)·ln(Q), to correct for non-standard conditions — concentrations other than 1 M — using the reaction quotient Q built from the product and reactant ion concentrations you supply and the number of electrons transferred, n, in the balanced redox reaction. The engine also converts cell potential into Gibbs free energy via ΔG = −nFE (both at standard conditions and at the actual Nernst-corrected conditions), and derives the equilibrium constant from ln(K) = nFE°/RT, tying together three ways chemists express the same underlying thermodynamic favorability.

A positive cell potential is flagged as spontaneous — the reaction runs forward as written without external energy input — while a negative one means the reverse reaction is favored instead. The most consequential input to get right is n, the electrons transferred: it must match the actual balanced half-reactions (values that appear directly in both the exponential Nernst term and the linear ΔG and lnK formulas), so an incorrect electron count skews every downstream number, not just one. Also note temperature here is entered in kelvin, not Celsius; 298.15 K is room temperature and the default, but forgetting the +273.15 offset when using a different temperature is a common data-entry slip.