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.