Cell EMF Calculator (Electromotive Force)
Calculate the EMF (electromotive force) of an electrochemical cell. Determine cell potential from standard electrode potentials or calculate using the Nernst equation for nonstandard concentrations.
Select the oxidizing agent (gets reduced)
Select the reducing agent (gets oxidized)
Concentration of cathode ion (default: 1 M)
Concentration of anode ion (default: 1 M)
Temperature in Celsius (default: 25°C)
What is cell EMF?
Electromotive force (EMF) is the maximum potential difference between two electrodes in an electrochemical cell. It represents the driving force that pushes electrons through the external circuit. Standard EMF (E°_cell) is measured under standard conditions (1 M concentrations, 1 atm pressure, 25°C). A positive EMF indicates a spontaneous reaction.
How do you calculate cell EMF?
E_cell = E_cathode - E_anode. For standard conditions: simply subtract the standard reduction potentials. For nonstandard conditions, use the Nernst equation: E = E° - (RT/nF)ln(Q), where n = electrons transferred, Q = reaction quotient. At 25°C: E = E° - (0.0591/n)log(Q).
What is the Nernst equation?
The Nernst equation relates cell potential to concentration: E = E° - (RT/nF)ln(Q). At 298 K (25°C): E = E° - (0.05916/n)log(Q). For dilution: E = E° - (0.05916/n)log([C_products]^coef / [C_reactants]^coef). This accounts for how concentration changes affect EMF.
Which metals make the best batteries?
The greatest EMF comes from combining the strongest oxidizing agent (highest E°) with the strongest reducing agent (lowest E°). Zn/Cu gives E° = +0.34 - (-0.76) = 1.10 V. Li/F₂ would give ~5.6 V but is impractical. Common batteries: alkaline (Zn/MnO₂, ~1.5V), lead-acid (Pb/PbO₂, ~2V), lithium-ion (~3.7V).
What is standard electrode potential?
Standard electrode potential (E°) is measured relative to the hydrogen electrode (defined as 0 V). Positive E° means stronger oxidizing agent; negative E° means stronger reducing agent. Fluorine has the highest E° (+2.87V), making it the strongest oxidizer; lithium has the lowest (-2.93V), making it the strongest reducer.