General Chemistry Principles, Patterns, and Applications, 2011

. Zn 2+ (aq) + Pb(s) → Zn(s) + Pb 2+ (aq)
11. Each reaction takes place in acidic solution. Balance each reaction and then determine whether it occurs
spontaneously as written under standard conditions.
a. Se(s) + Br 2 (l) → H 2 SeO 3 (aq) + Br − (aq)
b. NO 3 − (aq) + S(s) → HNO 2 (aq) + H 2 SO 3 (aq)
c. Fe 3+ (aq) + Cr 3+ (aq) → Fe 2+ (aq) + Cr 2 O 7 2− (aq)
12. Calculate E° cell and ΔG° for the redox reaction represented by the cell diagram Pt(s)∣ Cl 2 (g, 1 atm)∥ ZnCl 2 (aq, 1
M)∣ Zn(s). Will this reaction occur spontaneously?
13. If you place Zn-coated (galvanized) tacks in a glass and add an aqueous solution of iodine, the brown color of
the iodine solution fades to a pale yellow. What has happened? Write the two half-reactions and the overall
balanced chemical equation for this reaction. What is E° cell ?
14. Your lab partner wants to recover solid silver from silver chloride by using a 1.0 M solution of HCl and 1 atm
H 2 under standard conditions. Will this plan work?
A N S W E R S
1. Pt(s)∣ H 2 (g, 1 atm) | H + (aq, 1M)∥ Cu 2+ (aq)∣ Cu(s)
2.
3.
a. Cl 2 (g) + H 2 (g) → 2Cl − (aq) + 2H + (aq); E° = 1.358 V
b. Br 2 (l) + 2Fe 2+ (aq) → 2Br − (aq) + 2Fe 3+ (aq); E° = 0.316 V
c. 2Fe 3+ (aq) + Cd(s) → 2Fe 2+ (aq) + Cd 2+ (aq); E° = 1.174 V
[1] Concentrated solutions of salts (about 1 M) generally do not exhibit ideal behavior, and the actual standard
state corresponds to an activity of 1 rather than a concentration of 1 M. Corrections for nonideal behavior are
important for precise quantitative work but not for the more qualitative approach that we are taking here.
[2] As we shall see in Section 19.7 "Electrolysis", this does not mean that the reaction cannot be made to occur at
all under standard conditions. With a sufficient input of electrical energy, virtually any reaction can be forced to
occur.
19.3 Comparing Strengths of Oxidants and Reductants
L E A R N I N G O B JE C T I V E
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