Question

These equations below show two standard reduction potentials.

Which value represents the standard cell potential of the spontaneous overall reaction?

Answer 1

We have
Mn2+ + 2e- → Mn (reduction)
Fe2+ → Fe3+ + e- (oxidation)

Since reduction occurs at the cathode, the cathode is Mn(s).
The overall cell potential is
Ecell = Ered,cathode - Ered,anode
= -1.18 - 0.77
= -1.95V

The reaction is spontaneous since Ecell is negative.