HardChemistryHigh School (11–12)ElectrochemistryNumerical

Two half-reactions are known. Cr³⁺ + e⁻ → Cr²⁺ has E° = -0.41 V…

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Two half-reactions are known. $\text{Cr}^{3+} + e^- \rightarrow \text{Cr}^{2+}$ has $E^\circ = -0.41\ \text{V}$ . $\text{Cr}^{2+} + 2e^- \rightarrow \text{Cr}$ has $E^\circ = -0.91\ \text{V}$ . Find the Gibbs energy change for $\text{Cr}^{3+} + 3e^- \rightarrow \text{Cr}$ and the standard potential of $\text{Cr}^{3+}/\text{Cr}$ .

Need a reminder? The key ideaShow

$\Delta G^\circ = -nFE^\circ$ , with $F = 96500\ \text{C/mol}$ , and $E^\circ = \dfrac{0.0591\ \text{V}}{n}\log K$ at $298\ \text{K}$ . A reaction with $E^\circ > 0$ has $\Delta G^\circ < 0$ and $K > 1$ . When half-reactions with different numbers of electrons are added, add the Gibbs energies, not the potentials.

The worked solution

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