X. Electrochemistry
Key focus of this chapter: reduction potential
This chapter focuses on reduction potential and gives concise summaries of the important things about reduction half-reaction, electrochemical cells, standard free-energy change, and quantitative electrolysis in more detail.
A. Reduction half-reaction, Eo (V)
: magnitude of ability to accept electrons by comparing with the standard hydrogen electrode
(2H+(aq) + 2e– → H2(g) Eo = 0 V)
1. Standard electrode potential
 | Meaning |
 | Easily release electrons rather than hydrogen → oxidation |
 | Easily accept electrons rather than hydrogen → reduction |
Reduction half-reaction |  | Strength oxidation (Anode) | Strength reduction (Cathode) |
 |  |  |  |
- Qs/ Which of the following represents the reaction for the strongest reduction in a galvanic cell?
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ANS: C
The strong reduction means the strong ability to accept electron(s). Therefore, the most positive standard reduction potential is + 0.80V
2. Anode and cathode
Meaning | Galvanic cells | Electrolytic cells | |
Anode | Releasing electron (oxidation) | Negative (-) | Positive (+) |
Cathode | Accepting electron (reduction) | Positive (+) | Negative (-) |
B. Reduction petential in cells
1. Electromotive force (E.M.F.)
: the difference of electric potential force between anode and cathode
- The decision of spontaneous or non-spontaneous reaction by the value of overall Eocell from Eoreduction + Eooxidatio.
• Qs/ Determine if the reaction is a spontaneous or non-spontaneous reaction.
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2. Shorthand notation
- Ex/ Shorthand notation from the spontaneous reaction between Cu(s) and Ag(s).
Processing | Reactions | |
Reduction half-reaction |  | |
Oxidation and reduction |  | |
Multiply coefficient to cancel electrons |  | |
 |  | |
Shorthand notation and meaning for galvanic cell | Shorthand notation |  |
Meaning for galvanic cell |  | |
C. Electrochemical cells
: generating an electric current by reaction between oxidation and reduction.
Cell type | Features | |
 | Voltaic cell |  |
Daniell cell |  | |
 |  | |
D. Standard free-energy change
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Qs/ Calculate the standard free-energy change, ΔG, from the reaction.
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E. Quantitative electrolysis
1. Charge, C
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2. Faraday, F
Qs/ Calculate Faraday when a direct current of 5.0 A is passed through an aqueous solution of AgNO3 for 32 minutes and 10 seconds.
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Qs/ How many grams of Pb are produced from a lead storage battery when this battery is charged for 42 minutes and 50 seconds with a constant current of 2A?
PbSO4(s) + H+(aq) + 2e– → Pb(s) + HSO4–(aq)
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