Electrochemistry
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Transcript of Electrochemistry
![Page 1: Electrochemistry](https://reader035.fdocuments.in/reader035/viewer/2022062418/5550638eb4c90574428b54f4/html5/thumbnails/1.jpg)
Electrochemistry
Electrode Potentials
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Electrochemistry
1. What are electrode potentials?
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Electrochemistry
1. What are electrode potentials?
• Electric potential arising from the separation of charges in the equilibrium in a redox half equation.
• It is measured with respect to S.H.E.
Examples:
Zn2+ (aq) + 2e– Zn ⇌ (s)
Fe3+ (aq) + e– Fe⇌ 2+ (aq)
2H+ (aq) + e– H⇌ 2 (g)
Cu2+ (aq) + 2e– Cu (s)⇌
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Electrochemistry
2. What can we know from electrode potentials?
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Electrochemistry
2. What can we know from electrode potentials?
1. [Sign]
+ forward reaction (reduction) favoured
– backward reaction (oxidation) favoured
2. [Magnitude]
– the extent the reaction is favoured
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Electrochemistry
3. How can we measure standard electrode potentials?
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Electrochemistry
3. How can we measure standard electrode potentials?
- connect the half cell that you wish to study to the SHE
Note:• You need to be know how to draw the cell setup.• Things to note when drawing half cell: (1) salt bridge, (2)
voltmeter and (3) ensure all gases, solutions are at standard conditions.
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Electrochemistry
4. How can we use standard electrode potentials?
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Electrochemistry
4. How can we use standard electrode potentials?
- to predict whether a redox reaction is feasible when 2 species are mixed.
Examples:
I2 + Cr2+ feasible?
V3+ + Cu2+ feasible?
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Electrochemistry
4. How can we use standard electrode potentials?
Strategy
1. Identify possible oxidation/ reduction reactions
2. Find electrode potentials for these half equations
3. Calculate Ecell = Ered – Eox
Ecell
+ feasible
– not feasible
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Electrochemistry
Galvanic Cells
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Electrochemistry
5. How to distinguish anode and cathode?
Galvanic Cell
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Electrochemistry
5. How to distinguish anode and cathode?
Positive remove electrons Reduction Cathode
Negative produce electrons Oxidation Anode
Electrons flow from AC
Galvanic Cell
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Electrochemistry
6. How to draw cell diagram?
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Electrochemistry
6. How to draw cell diagram?
Example
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Electrochemistry
6. How to draw cell diagram?
1. Anode || Cathode
2. Electrodes at the extreme ends.
3. Anode: Fe2+ Fe3+
Cathode: H+ H2
4. If redox species of the same phase, separate by comma; different phase by |
Pt (s) | Anode || Cathode | Pt (s)
Pt (s) | Fe2+ Fe3+ || H+ H2 | Pt (s)
Pt(s) | Fe2+, Fe3+(aq) || H+(aq) | H2(g) | Pt(s)
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Electrochemistry
Electrolytic Cells
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Electrochemistry
7. How to distinguish anode and cathode?
Electrolytic Cell
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Electrochemistry
7. How to distinguish anode and cathode?
Positive attract anions oxidized Anode
Negative attract cations reduced Cathode
Electrons flow from AC
Electrolytic Cell
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Electrochemistry
8. How to predict what species is discharged?
1. Identify all ions in solution (including H2O)
2. Cations attracted to cathode;
Anions attracted to anode
3. Find electrode potentials for these half equations
E°
Cathode more positive or less negative is discharged
Anode more negative or less positive is discharged
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Electrochemistry
Calculations (Strategy)
Question will surely involve 1 or more of the formulas:
Q = I t = n F
I: current (A) n: moles of electrons!
t: time (s) F: Faradays constant (96500 C/mol)
F = Le L: Avogadro’s constant
e: 1.6 x 10–19 C