Question

For a galvanic cell, the following half reactions are given. Decide, which will remain as reduction reaction and which will be reversed to become an oxidation reaction. Give reason for your answer.
(I) Cr³⁺ + 3e⁻ → Cr(s); E° = −0.74 V
(II) Fe²⁺ + 2e⁻ → Fe(s); E° = −0.44 V

Hint:

In a galvanic cell, the substance with the higher reduction potential is reduced, and the other is oxidized.

Answer 1

In the case of galvanic cells, the half-reaction with a higher reduction potential (more positive) will occur as the reduction reaction, while the half-reaction with the lower reduction potential will undergo oxidation. - For reaction (I), Cr^{3+} + 3e^{-} \rightarrow \text{Cr(s)} with E^\circ = -0.74 V will undergo oxidation. - For reaction (II), Fe^{2+} + 2e^{-} \rightarrow \text{Fe(s)} with E^\circ = -0.44 V will remain as the reduction reaction. Thus, reaction (II) remains as a reduction reaction, and reaction (I) will be reversed to become oxidation.