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
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.
A half-cell called standard hydrogen electrode
represented by Pt(s) l H2(g) l H+(aq), is assigned
a zero potential at all temperatures corresponding to the reaction
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=