** Nernst Equation **

- The basic
**Nernst Equation**is written as -

**E = E**^{o}- (RT/nF)lnQ

- The Nernst equation is derived from thermodynamic considerations.

- The reactants' free energies are expressed as electrical potentials.

- The term
**E**is the standard electric potential of the reference electrode^{o}

- The term
**lnQ**represents the natural logarithm (ln) of the reaction quotient (Q) of the species involved.

**lnQ**can be expressed as a logarithm to the base 10 by -

**2.303 log**._{10}Q

and**log**, for pH measurements, can be expresses in terms of the hydrogen ion activity by -_{10}Q

**-log**which is the_{10}a_{H+}**pH**of a solution.

Hence the equation becomes -

**R * T**

**E**= **E**^{o}+ **----------- * 2.303 pH****n * F**

- The constants of the
**Nernst equation**-

**R**is the universal gas constant -

**R**= 8.3145 J/mol.K (Joule per mol and per Kelvin)

**n**is the number of moles of electrons transferred in the balanced equation or the charge/valency of the ion. Which in the case of the hydrogen ion -

**n**= 1

**F**is the Faraday constant which is the electrical charge in coulombs (C) for every mole (mol) of reactant involved in the electrochemical cell -

**F**= 96485.309 C/mol

- At a temperature (
**T**) of 298.15^{o}K (25^{o}C) the**Nernst equation**can be rewritten as -