Exam 4B, Spring 1999

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

a. K(g) → K(s)

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

c. CuCO₃(s) + 2 HNO₃(aq) → CO₂(g) + H₂O(l) + Cu²⁺(aq) + 2 NO₃^–(aq)

2. Complete and balance the following reactions:

a. HPO₄^2–(aq) + NaOH(aq)

b. CaCl₂(aq) + Na₂SO₄(aq)

c. CrO₄^2–(aq) + Fe(s) → Cr³⁺(aq) + Fe²⁺(aq) pH = 1

d. MnO₄^–(aq) + NO₂^–(aq) → MnO₂(s) + NO₃^–(aq) pH = 14

3. Consider the formation of the complex ion Cd(NH₃)₄²⁺(aq).

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

b. The following cell is constructed: Cd(s)|Cd²⁺(aq)|| Cd(NH₃)₄²⁺(aq)|NH₃(aq)|Cd(s); what is E° for the cell?

4. Consider the reaction: CaO(s) + HCl(aq) → H₂O(l) + Ca²⁺(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: Zn(s) | Zn²⁺(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.

Answers