Nernst equation

A basic equation of biophysics that describes the relationship between the equilibrium potential difference across a semipermeable membrane, and the equilibrium distribution of the ionic permeant species. It is described by: E = -(RT/zF).ln(C2/C1), where E is the potential on side 2 relative to side 1 (in volts), R is the gas constant (8.314 J K-1 mol-1 ), T is the absolute temperature, z is the charge on the permeant ion, F is the Faraday constant (96,500 C mol-1) and C1 and C2 are the concentrations (more correctly activities) of the ions on sides 1 and 2 of the membrane. It can be seen that this equation is a solution of the more general equation of electrochemical potential, for the special case of equilibrium. The equation described the voltage generated by ion-selective electrodes, like the laboratory pH electrode; and approximates the behaviour of the resting plasma membrane (see resting potential).