Exam 4A, Spring 1999

1. Predict the sign of ΔS° for the following reactions.

a. Na(s) → Na(g)

b. Cl₂(g) + 2 H₂O(l) → Cl^–(aq) + HClO(aq) + H₃O⁺(aq)

c. CO₂(g) + 3 H₂O(l) + Ca(NO₃)₂(aq) → CaCO₃(s) + 2 H₃O⁺(aq) + 2 NO₃^–(aq)

2. Complete and balance the following reactions:

a. HCO₃^–(aq) + KOH(aq)

b. AgNO₃(aq) + NaCl(aq)

c. CrO₄^2–(aq) + Cu(s) → Cr³⁺(aq) + Cu²⁺(aq) pH = 1

d. Mn²⁺(aq) + H₂O₂(aq) → MnO₂(s) + H₂O(l) pH = 14

3. Consider the formation of the complex ion Ag(NH₃)₂⁺(aq).

a. Find ΔG° for the reaction at 25 °C.

b. The following cell is constructed: Ag(s)|Ag⁺(aq)|| Ag(NH₃)₂⁺(aq)|NH₃(aq)|Ag(s); what is E° for the cell?

4. Consider the reaction: MgO(s) + HCl(aq) → H₂O(l) + Mg²⁺(aq) + Cl^–(aq).

a. Find ΔH° for the reaction.

b. Find ΔS° for the reaction.

c. Find ΔG° for the reaction at 25 °C.

d. Is the reaction spontaneous?

5. The following cell was constructed: Sn(s)|Sn²⁺(aq)|| I₂(s)|I^–(aq)|Pt.

a. Write the balanced reaction for the cell.

b. Find E° for the cell.

c. Find the thermodynamic equilibrium constant for the cell at 25 °C.

d. The concentration of ions in the anode half-cell are 0.10 M and the concentration of ions in the cathode half-cell are 0.050 M; find the cell potential at 25 °C.

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