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Redox and electrode potentials

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Question 12

Four redox systems relevant to hydrogen–oxygen fuel cells are shown below:

Redox systemE∘ / VH2O(l)+e−⇌OH−(aq)+12H2(g)−0.83H+(aq)+e−⇌12H2(g)+0.0012O2(g)+H2O(l)+2e−⇌2OH−(aq)+0.4012O2(g)+2H+(aq)+2e−⇌H2O(l)+1.23 \begin{array}{|c|c|} \hline \text{Redox system} & E^\circ \text{ / V} \\ \hline \text{H}_2\text{O(l)} + \text{e}^- \rightleftharpoons \text{OH}^-\text{(aq)} + \frac{1}{2}\text{H}_2\text{(g)} & -0.83 \\ \text{H}^+\text{(aq)} + \text{e}^- \rightleftharpoons \frac{1}{2}\text{H}_2\text{(g)} & \phantom{+}0.00 \\ \frac{1}{2}\text{O}_2\text{(g)} + \text{H}_2\text{O(l)} + 2\text{e}^- \rightleftharpoons 2\text{OH}^-\text{(aq)} & +0.40 \\ \frac{1}{2}\text{O}_2\text{(g)} + 2\text{H}^+\text{(aq)} + 2\text{e}^- \rightleftharpoons \text{H}_2\text{O(l)} & +1.23 \\ \hline \end{array} Redox systemH2​O(l)+e−⇌OH−(aq)+21​H2​(g)H+(aq)+e−⇌21​H2​(g)21​O2​(g)+H2​O(l)+2e−⇌2OH−(aq)21​O2​(g)+2H+(aq)+2e−⇌H2​O(l)​E∘ / V−0.83+0.00+0.40+1.23​​

Which statement(s) is/are correct for an alkaline hydrogen–oxygen fuel cell?

  1. The reaction at the negative electrode is: OH−(aq)+12H2(g)→H2O(l)+e−\displaystyle \text{OH}^-\text{(aq)} + \frac{1}{2}\text{H}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)} + \text{e}^-OH−(aq)+21​H2​(g)→H2​O(l)+e−.
  2. The overall cell reaction is: H2(g)+12O2(g)→H2O(l)\displaystyle \text{H}_2\text{(g)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)}H2​(g)+21​O2​(g)→H2​O(l).
  3. The standard cell potential is 0.43 V.

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Redox and electrode potentials Questions

  1. A Level
  2. /Chemistry
  3. /Redox and electrode potentials