given MnO2/Mn+2 and Cr+3/Cr half cells, determine the overall electrochemical reaction that proceeds spontaneously and the E^0 values
The overall electrochemical reaction that proceeds spontaneously when the MnO2/Mn+2 and Cr+3/Cr half cells are combined in a galvanic cell is:
MnO2 + 4H+ + 2e- -> Mn+2 + 2H2O E^0 = 1.23V
Cr+3 + 3e- -> Cr E^0 = -0.74V
Overall reaction:
MnO2 + 4H+ + Cr+3 -> Mn+2 + Cr + 2H2O E^0 = 1.23V + (-0.74V) = 0.49V
So the overall reaction is:
MnO2 + 4H+ + Cr+3 -> Mn+2 + Cr + 2H2O
with E^0 = 0.49V.