Deduced from the following values of half cells, what combination of two half cells would result in — Electrochemistry Chemistry Question
Question
Deduced from the following $E^\circ$ values of half cells, what combination of two half cells would result in a galvanic cell with the largest positive standard cell potential? (i) $A^{3-} \rightarrow A^{2-} + e^-$, $E^\circ = 1.5\text{ V}$; (ii) $B^{2+} + e^- \rightarrow B^+$, $E^\circ = 2.1\text{ V}$; (iii) $C^{2+} + e^- \rightarrow C^+$, $E^\circ = +0.5\text{ V}$; (iv) $D \rightarrow D^{2+} + 2e^-$, $E^\circ = -1.5\text{ V}$. Note: The potentials given are strictly for the reactions exactly as written.
💡 Solution & Explanation
The largest cell potential is formed by combining the strongest oxidation and the strongest reduction. The given half-reactions are: (i) oxidation ($E_{ox} = 1.5\text{ V}$), (ii) reduction ($E_{red} = 2.1\text{ V}$), (iii) reduction ($E_{red} = 0.5\text{ V}$), (iv) oxidation ($E_{ox} = -1.5\text{ V}$). The maximum positive potential is generated by combining the best oxidation (i) and the best reduction (ii): $E^\circ_{cell} = 1.5\text{ V} + 2.1\text{ V} = 3.6\text{ V}$.