Three aqueous half-cell couples are available under standard conditions at 298 K: 1
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
Three aqueous half-cell couples are available under standard conditions at 298 K:
1. MnO4⁻(aq) + 8 H⁺(aq) + 5 e⁻ → Mn2+(aq) + 4 H2O(l) E° = +1.51 V
2. Fe3+(aq) + e⁻ → Fe2+(aq) E° = +0.77 V
3. Br2(l) + 2 e⁻ → 2 Br⁻(aq) E° = +1.07 V
A student constructs a cell in which permanganate ions in acidic solution are allowed to react with bromide ions, producing Mn2+ and Br2 under standard conditions.
(a) Write the balanced overall chemical equation, including states of matter, for the spontaneous reaction between the appropriate species from the list above.
(b) Calculate the standard cell potential for the reaction you wrote in part (a).
(c) Using your result from part (b), calculate the standard Gibbs free-energy change, in kilojoules per mole of reaction, for the overall reaction. Clearly indicate the value of the stoichiometric factor that you use in your calculation.
(d) Determine the equilibrium constant, K, for the reaction at 298 K.
(e) Classify the cell as galvanic or electrolytic under standard conditions and justify your classification using the numerical results obtained in parts (b)–(d).