A research lab is constructing a series of galvanic cells at 298 K by pairing the…

CHEMISTRY · Multi-part · A Level · Chemistry · Electrode potentials · Electrode potentials

Problem

A research lab is constructing a series of galvanic cells at 298 K by pairing the four half-reactions in the table. Each half-reaction can be used in either its oxidation or reduction direction.

Label	Half-Reaction	$E^{\circ}_{\text{red}}$ (V)
1	$\text{D}^{2+}+2e^{−}\rightarrow \text{D}$	$+0.34$
2	$\text{E}^{3+}+3e^{−}\rightarrow \text{E}$	$−0.20$
3	$\text{F}^+ + e^{−}\rightarrow \text{F}$	$+1.10$
4	$\text{G}^{2+}+2e^{−}\rightarrow \text{G}$	$−0.44$

(a) List all unique, non-degenerate overall reactions that can be produced by pairing two different half-reactions from the table (one operating as an oxidation and the other as a reduction). For each reaction, specify the direction of electron flow for each half-reaction. (b) For every overall reaction identified in part (a), balance the reaction, calculate

E^{\circ}_{\text{cell}}

, and state the corresponding value of

n

. (c) Rank the overall reactions from the one expected to have the most negative

\Delta G^{\circ}

(i.e., most favorable) to the one with the least negative

\Delta G^{\circ}

. Identify any ties based on

E^{\circ}_{\text{cell}}

. (d) When a tie exists in

E^{\circ}_{\text{cell}}

, apply the quantitative relationship between

\Delta G^{\circ}

n

, and

E^{\circ}_{\text{cell}}

to break the tie. Provide the final ranking that accounts for both

E^{\circ}_{\text{cell}}

and

n

. (e) Choose the reaction that your analysis indicates is most thermodynamically favorable. Explain, in one or two well-organized paragraphs, how both half-reaction potentials and the stoichiometry of electron transfer combine to make this reaction particularly favorable compared with the alternatives.

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