For the first row of transition metals the E0 values are
Fe = -0.44
Explain the irregularities in the above values ?
The Standard Electrode Potential (E0 values for M2+/M as well as for M3+/M2+) depend on the thermochemical parameters such as enthalpies and ionization energies.
There is no regular trend in the E0 values of first transiytion element is because their ionization enthalpies (IE1 + IE2) and submlimation enthalpies do not show any regular trend. The general trend towards less negative E0 values along the series is due to the general increase in the sum of first and second ionization enthalpies.