Nernst Equation Calculator

The Nernst equation adjusts a standard electrode or cell potential for the actual temperature and chemical activities in an electrochemical system. Standard potentials describe a specified reference state, but batteries, corrosion cells, sensors, and laboratory reactions often operate with nonstandard concentrations or gas pressures. The equation connects those conditions to voltage through E = E standard minus (RT divided by nF) times the natural logarithm of Q. In that expression, E is the nonstandard potential in volts, E standard is the standard potential, R is the universal gas constant 8.314462618 joules per mole-kelvin, T is absolute temperature in kelvin, n is the number of electrons transferred in the balanced redox reaction, F is Faraday's constant 96485.33212 coulombs per mole, and Q is the dimensionless reaction quotient. The calculator uses these physical constants directly and reports both the resulting potential and the correction subtracted from the standard value. The reaction quotient is built from product activities divided by reactant activities, with each activity raised to its stoichiometric coefficient. Pure solids and pure liquids are omitted because their standard-state activities are one. Dilute solution concentrations and ideal-gas pressure ratios are often used as activity approximations in introductory calculations. Q must be positive because the logarithm of zero or a negative number is undefined. When Q equals one, its logarithm is zero and the calculated potential equals the standard potential. A Q greater than one makes the logarithmic term positive and lowers the potential for the reaction as written. A Q below one gives a negative logarithm, so subtracting the correction raises the potential. The size of the change grows with temperature and shrinks as the number of transferred electrons increases. At 25 degrees Celsius, the base-ten form is often written with approximately 0.05916 divided by n, but this calculator uses the general natural-log form so it works at any positive temperature. Use a consistently balanced overall reaction when identifying n and constructing Q. Reversing the reaction changes the sign of the standard potential and replaces Q with its reciprocal. Potentials predict thermodynamic driving force under the entered assumptions; they do not predict reaction rate, current, internal resistance, or kinetic overpotential. For precise work, replace concentration approximations with activities and use conditions appropriate to the electrochemical convention being applied.