1.1 What is Chemistry?

http://www.ck12.org Chapter 23. Electrochemistry

The Nernst Equation

Up to this point, our discussion of cell potentials has focused on the standard states. However, in real life we will
rarely be using standard state conditions, so we need a way to work with more practical situations. For conditions
that are not standard-state, we use the Nernst equation, named after the German chemist Walther Nernst (winner of
the 1920 Nobel Prize in Chemistry).

FIGURE 23.10

Walther Nernst.

The Nernst equation has the following form:

E=E◦−RTnFln Q

where E is the reaction potential under the actual conditions, E° is the reaction potential under standard conditions, R
is the universal gas constant (8.314 J/K•mol), T is the temperature (in Kelvin), n is the number of moles of electrons
transferred in the redox reaction, F is a value known as the Faraday constant (96,485 C/mol), and Q is the reaction
quotient. Recall that the reaction quotient takes the same form as the equilibrium constant expression, except that
it is true even when the reaction is not at equilibrium. For example, the reaction quotient for the following generic
reaction is given below: