23. Given the standard free energy of formation of is -237.2 kJ/mol, and for its ionization into and — Electrochemistry Chemistry Question
Question
23. Given the standard free energy of formation of $H_2O(l)$ is -237.2 kJ/mol, and $\Delta G^\circ$ for its ionization into $H^+$ and $OH^-$ is 80 kJ/mol. Calculate the standard EMF of the cell: $Pt / H_2(1 bar) / H^+(1 M) // OH^-(1 M) / O_2(1 bar) / Pt$ at 298 K.
Answer: A
💡 Solution & Explanation
Anode: $H_2 \rightarrow 2H^+ + 2e^-$. Cathode: $1/2 O_2 + H_2O + 2e^- \rightarrow 2OH^-$. Overall: $H_2 + 1/2 O_2 + H_2O \rightarrow 2H^+ + 2OH^-$. $dG^\circ = dG^\circ_{formation}(H_2O) + 2 \times dG^\circ_{ionization} = -237.2 + 2(80) = -77.2 kJ = -77200 J$. $dG^\circ = -nFE^\circ \implies -77200 = -2 \times 96500 \times E^\circ \implies E^\circ = 0.40 V$.
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