The concentration of all species involved in the species involved in the electrode reaction is unity.This need not be always true.
Nernst shows that for the electrode reaction:
the electrode potential at any concentration measured with respect to standard hydrogen electrode can be represented by:
but concentration of solid M is taken as unity as we have
R is gas constant (8.314 JK–1 mol–1),
F is Faraday constant (96487 C mol–1), T is temperature in kelvin and [Mn+] is the concentration of the species, Mn
Let us take a electrode reaction
The Nernst equation of this electrode
Instead of activity, we can take molar concentration.
For pure solid and liquid molar concentration is taken as unity.
Strong electrolytes: The molar conductivity of a strong electrolyte decreases slightly with the increase in concentration. This decrease is due to the increase in interionic attractions as a result of greater numbr of ions per unit volume. With dilution, the ions are far apart, inter ionic attractions become weaker and conductance increases
Nernst equation is given as:
Ecell =
Where Q reaction quotient
Ecell is the cell potential at the temperature of interest.
is the standard cell potential
R is the universal gas constant
T is the abolute temperture
F is the Farday constant
n i the number of electron
At equilibrium
Ecell =0 and Q=k
K isthe equilibrium constant
0=
Fuel cell: A galvanic cell in which the reactants are continuously fed into the cell and the products are continuously removed is called a fuel cell.
The most important fuel cell is hydrogen oxygen fuel cell