Electron Transfer Reactions · Paper 2 — Free Chemistry SL Practice Questions

Vanadium(V) oxide ($\text{V}_2\text{O}_5$) is used as a catalyst in the Contact Process for the manufacture of sulfuric acid. In one step of the catalytic cycle, $\text{V}_2\text{O}_5$ is reduced to vanadium(IV) oxide ($\text{VO}_2$) by sulfur dioxide ($\text{SO}_2$), producing sulfate ions ($\text{SO}_4^{2-}$). In a subsequent step, $\text{VO}_2$ is re-oxidised back to $\text{V}_2\text{O}_5$ by oxygen gas. Standard electrode potentials at $298\,\text{K}$: $$\text{SO}_4^{2-}(\text{aq}) + 4\text{H}^+(\text{aq}) + 2e^- \rightleftharpoons \text{SO}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l}) \quad E^\circ = +0.17\,\text{V}$$ $$\text{V}_2\text{O}_5(\text{s}) + 2\text{H}^+(\text{aq}) + 2e^- \rightleftharpoons \text{V}_2\text{O}_4(\text{s}) + \text{H}_2\text{O}(\text{l}) \quad E^\circ = +1.00\,\text{V}$$ The Contact Process operates at approximately $450\,°\text{C}$.