Nernst Equation: The cell potential of a half cell (as well as that of a complete cell) depends upon the concentrations of involved ions, pressure of the gaseous species (if involved) and the temperature. The relation connecting them is given by the Nernst equation.
It is expressed as
E = E° - (RT/nF)ln Q°
Q° = Product of concentration (or pressure) of products each raised to the corresponding stochiometric number/Product of concentration (or pressure) of reactants each raised to the corresponding stochiometric number
n = number of electrons involved in the hall cell reaction