What does the Nernst equation do?
Finds a cell's actual voltage under real conditions, not just the ideal standard value - correcting for the real concentrations via Q.
// chemistry › Cell Potential
Nernst Equation
Calculate cell voltage E = E° − (0.0591/n)logQ, with symbol legend and real-world examples.
E = E\circ - \frac{0.0591}{n}\log Q
A mind behind this: Walther Nernst 1864–1941
Frequently asked questions
Why does a battery's voltage drop as it's used?
As it runs, reactants are consumed and Q rises, so the equation gives a lower voltage. When it reaches equilibrium the voltage hits zero - the battery is dead.
What is the 0.0591 term?
A bundled constant for 25°C: it is RT/F converted from natural log to base-10 log, the value that appears for room-temperature cells.
Why divide by n?
n is the electrons moved per cycle. Reactions moving more electrons are less sensitive to concentration per volt, so dividing by n scales the correction.
Where is it used?
Batteries and fuel cells, electroplating, corrosion protection, and the electrical signals of nerve and muscle cells. pH meters use it too.