Silver is extracted from its ore via the leaching process for the cyanide ion in that ore. Shown below is the overall reaction.
4 Ag (s) + 8 CN⁻ (aq)  + O₂ (g) + 2 H₂O (l) → 4 [Ag(CN)₂]⁻ (aq) + 4 OH⁻ (aq)
Use the given data to calculate ΔG° for the above reaction at 25 °C.


Ag⁺ (aq) + 2 CN⁻ (aq) → Ag(CN)₂⁻ (aq);    K_f = 3.00×10²⁰
H₂O (l) ⇌ H⁺ (aq) + OH⁻ (aq);                   K_w = 1.00×10⁻¹⁴ 
O₂ (g) + 4 H⁺ (aq) + 4 e⁻ → 2 H₂O (l);        E° = 1.229 V
Ag⁺ (aq) + e⁻ → Ag (s);                              E° = 0.800 V

• A. ΔG° = 931 kJ
• B. ΔG° = −930 kJ
• C. ΔG° = −588 kJ
• D. ΔG° = −313 kJ

Answer: (D)