Strengths of Oxidizing and Reducing Agents; Free Energy and Redox Reactions

Name ______Date ______Period ___

Homework

Chapter 20: Electrochemistry

Exercises: Sections 20.4, 20.5:

Strengths of Oxidizing and Reducing Agents; Free Energy and Redox Reactions

1. (a) A Standard Reduction PotentialTable shows reduction half-reactions and reduction

potentials for various elements and ions. From top to bottom, the reduction potentials are listed

from the most (+) to the most (−). Would you expect to find strong oxidizers near the top or the

bottom of the list? Explain.

(b) Does the oxidant appear on the left or on the right side of a reduction half-reaction? Explain.

2. While looking at a table of standard reduction potentials (Appendix E in the textbook, or Green Sheets from

AP), choose the substance from the following pairs, that is the stronger oxidizing agent.

(a) Cl2(g) or Br2(g)

(b) Ni2+(aq) or Cd2+(aq)

(c) BrO3-(aq) or IO3-

(d) H2O2(aq) or O3(g)

3. From each of the following pairs of substances, use data in Appendix E to choose the one that is the stronger

reducing agent:

4. From each of the following pairs of substances, use data in Appendix E to choose the one that is the

stronger reducing agent.

(a) Ca(s) or Mg(s)

(b) Mn(s) or Al(s)

(c) H2(g, acidic solution) or H2S (g)

(d) H2SO3(aq) or H3AsO3(g)

5. Is each of the following substances likely to serve as strong oxidant, a weak oxidant, a strong reductant, or

Explain your choices.

(a) Na(s)

(b) O3(g)

(d) Ca2+(aq)

6. Based on the data in Appendix E,

(a) Which of the following is the strongest oxidizing agent, and which is the weakest? Explain.

Ce4+ Br2 H2O2 Zn

(b) Which of the following is the strongest reducing agent, and which is the weakest? Explain.

F- Zn N2H5+ I2 NO

7. The standard reduction potential for the reduction of RuO4-(aq) toRuO42-(aq) is +0.59V. By using Table

20.1 on page 857 of the textbook, suggest one or more substances that can oxidize RuO42-(aq) to RuO4 -(aq).

8. (a) What is the relationship between the emfof a reaction and the change in Gibbs free energy?

8. Continued:

(b) Calculate the standardemf and free-energy change at 25oC for each of the reactions below.

i. F2(g) + 2Cl-(aq) → 2F-(aq) + Cl2(g)

ii. Zn(s) + Ba2+(aq) → Zn2+(aq) + Ba(s)

8. Continued:

iii. 3Fe2+(aq) → Fe(s) + 2Fe3+(aq)

iv. Hg22+(aq) + 2Cu+(aq) → 2Hg(l) + 2Cu2+(aq)

(b) Which of the reactions in 8 (a) are spontaneous under standard conditions?

9. For each of the following reactions, write a balanced equation, calculate standard emf, and ΔGo at 298K.

(a) Aqueous iodide ion is oxidized to I2(s) by Hg22+(aq)

(b) In acidic solution copper (I) ion is oxidized to copper (II) ion by nitrate ion.

9. Continued:

10. How is Eocell related to the equilbrium constant, Keq?

11. If the equilibrium constant for a two-electron redox reaction at 298 K is 1.5 x 10 – 4, calculate the

corresponding ∆Go and Eocell under standard conditions.

12. Using the standard reduction potentials listed in appendix E, calculate the equilibrium constant for each of

the following reactions at 298 K:

(a) Fe(s) + Ni2+(aq) → Fe2+(aq) + Ni(s)

12. Continued:

(b) 10 Br – (aq) + 2 MnO4 – (aq) + 16 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 Br2(l)