The Born equation can be used for estimating the electrostatic component of Gibbs free energy of solvation of an ion. It is an electrostatic model that treats the solvent as a continuous dielectric medium (it is thus one member of a class of methods known as continuum solvation methods).
It was derived by Max Born.
where:
*N =  Avogadro constant
*z = charge of ion
*e = elementary charge, 1.6022 C
*&epsilon; = permittivity of free space
*r = effective radius of ion
*&epsilon; = dielectric constant of the solvent