Student Reader

Dielectric Constant

The dielectric constant (ε, Greek epsilon) is a property of a solvent. It is a measure of how well the solvent reduces interactions between ions in solution.

A dielectric constant greater than or equal to 20 means the medium is a good solvent (ie, at 20°C dH2O has an ε ≈ 80) and an ε below that means the medium is a poor solvent (ie,at 20°C acetic acid has an ε ≈ 6).

F = [ k · q1 · q2 ] / [ ε · r2 ]

FGiven two charges (ie, Na+ and Cl-, they exert a force F on each other, either attractive or repulsive.
kProportionality constant.
Magnitude of the charges.
rDistance between the charges.
εDielectric constant of the surrounding medium.
Dielectric ConstantComments