E0 value for the Mn3+/ Mn2+ couple is positive (+ 1.5 V) whereas that of Cr3+/ Cr2+ is negative (-0.4 V). Why?
Dear Student
The E0 value is standard electrode potential which depends on ionization energy. Since, Mn+2 ion gets a d5 configuration which is half filled and hence third ionization energy becomes much higher for the cation and it becomes more stable so it gets a higher positive E0 value, while the Cr+2 ion gets a d4 configuration and so it has less E0 value.
Regards
The E0 value is standard electrode potential which depends on ionization energy. Since, Mn+2 ion gets a d5 configuration which is half filled and hence third ionization energy becomes much higher for the cation and it becomes more stable so it gets a higher positive E0 value, while the Cr+2 ion gets a d4 configuration and so it has less E0 value.
Regards