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Redox Reactions and Electrochemistry
Redox Reactions and Electrochemistry
Redox Reactions and Electrochemistry Redox Reactions (19.1) Galvanic Cells (19.2) Standard Reduction Potentials (19.3) Thermodynamics of Redox Reactions (19.4) The Effect of Concentration on Cell Emf
(19.5) Batteries (19.6) Corrosion (19.7) Electrolysis (19.8) Electrometallurgy (19.9)
General Chemistry I – Concepts Representations of matter (1.3-1.4) Formula calculations and stoichiometry (3.6-
3.9) All concepts related to redox reactions
(assigning oxidation numbers, assigning oxidation versus reduction, balancing electrons between oxidation and reduction half-reactions and oxidizing and reducing agents), molar concentration, dilutions, and solution stoichiometry (4.5-4.6)
19.1 Redox Reactions
Review: How do we assign oxidation numbers?◦ Using “rules” from Chapter 4◦ Using electronegativity from Chapter 9
p. 248-249 of LA book
p. 248-249 of LA book
Figure 4.10, p 113
19.1 Redox Reactions
Review: How do we assign oxidation numbers?
Review: What is oxidation? Review: What is reduction? Review: What is an oxidizing agent? Review: What is a reducing agent? Review: What is a redox reaction? Consider the example of zinc and acid…
p. 249 of LA book
19.1 Redox Reactions
Balancing more complicated redox reactions:◦ Acidic solution◦ Basic solution
Half reactions and overall reactions:◦ Mass balanced◦ Charge balanced
What do these reactions have in common?
p. 250-251 of LA book
19.1 Redox ReactionsPractice:What is the balanced (net) redox reaction for the reaction of aqueous nitrate ion with copper to form copper(II) and nitric oxide in acidic solution?- What is the oxidizing agent?- What is the reducing agent?- How many electrons are transferred?- What does this look like?
p. 252 of LA book
19.1 Redox ReactionsPractice:What is the balanced (net) redox reaction for the reaction of aqueous permanganate with lead to form lead(II) and manganese dioxide in basic solution?- What is the oxidizing agent?- What is the reducing agent?- How many electrons are transferred?- What does this look like?
p. 253 of LA book
19.2 Galvanic Cells
Review: Reaction of zinc with acid:◦ This reaction is
spontaneous.◦ What would this
look like?
Figure 4.12, p 115
p. 254 of LA book
19.2 Galvanic Cells
Review: Reaction of zinc with acid:◦ This reaction is
spontaneous◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.14, p 117
p. 254 of LA book
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ This reaction is
spontaneous◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.13, p 116
p. 254 of LA book
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ This reaction is
spontaneous.◦ What would this
look like?◦ What is
happening with the electrons?
Figure 4.14, p 117
p. 254 of LA book
19.2 Galvanic Cells
Review: Reaction of zinc with copper(II):◦ What would the
half reactions look like?
Figure 4.13, p 116
p. 255 of LA book
19.2 Galvanic Cells
The reaction of zinc with copper(II):◦ What is happening with the electrons?
How can we measure this transfer of electrons (measure the number of electrons or the potential of these electrons)?
To insert a meter (or a device to use the energy), need to separate the half-reactions
p. 255 of LA book
19.2 Galvanic Cells
What is a “cathode”?What is an “anode”?
What is a salt bridge? What does it do?
p. 256 of LA book
Figure 19.1, p 665
19.2 Galvanic Cells
What is a galvanic or voltaic cell?Experimental apparatus for generating electricity through the use of a spontaneous reaction.
What is the measured potential? What is this called?
Figure 19.2, p 667
p. 257 of LA book
19.2 Galvanic Cells
What is “cell diagram” or “cell notation”?Conventional notation for representing galvanic cells
What is the cell diagram for this cell?
Practice:What is the cell diagram for:1. Aqueous lead ions reacting with zinc2. Aqueous copper ions reacting with lead3. Zinc metal reacting with acid
p. 257-258 of LA book
19.2 Galvanic Cells
Practice:What is the cell diagram for zinc metal reacting with acid
Figure 19.3, p 667
p. 258 of LA book
19.3 Standard Reduction PotentialsReview: All of these redox reactions are spontaneous: Zinc with aqueous
copper ions (standard cell potential of 1.10 V)
Lead with aqueous copper ions
Zinc with aqueous lead ions
Zinc with aqueous hydrogen ions
Figure 4.14, p 117
p. 258 of LA book
19.3 Standard Reduction Potentials
Zinc with aqueous copper ions (standard cell potential of 1.10 V)
Lead with aqueous copper ions Zinc with aqueous lead ions Zinc with aqueous hydrogen ions Can we measure a standard half-
reaction potential? What if we compare to a standard half-
reaction potential that is zero?
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
Zinc with aqueous hydrogen ions◦ Standard reduction potential (Eo
red) of:
◦ What is the standard oxidation potential (Eo
ox) of:
+ o22H aq 2e H g 0.0 V by definitionredE
+ o2H g 2H aq 2e ?oxE
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of zinc reacting with aqueous hydrogen ions
Figure 19.4, p 668
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard reduction potential of zinc?
Figure 19.4, p 668
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of copper reacting with aqueous hydrogen ions
Figure 19.4, p 668
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard reduction potential of copper?
Figure 19.4, p 668
p. 259 of LA book
19.3 Standard Reduction Potentials
What if we compare to a standard half-reaction potential that is zero?
What is the standard cell potential of copper reacting with aqueous zinc ions?
Figure 19.1, p 665
p. 260 of LA book
Table19.1, p 673
p. 260 of LA book
19.3 Standard Reduction Potentials
What does standard reduction potential (Eo
red) tell us? What are the rules for calculating
standard cell potential (Eo)?◦ Reversing the reaction◦ Intensive or extensive
What does standard cell potential (Eo) tell us?
p. 260-261 of LA book
19.3 Standard Reduction Potentials
Practice:What is the standard cell potential for the reactions of:
Lead with aqueous copper ions Zinc with aqueous lead ions
p. 261 of LA book
Table19.1, p 670
p. 261 of LA book
Will tin reduce iodine?
19.3 Standard Reduction Potentials
Table19.1, p 670
p. 261 of LA book
Will tin reduce iodine?Will silver reduce iodine?
19.3 Standard Reduction Potentials
19.3 Standard Reduction Potentials
Practice:What is a stronger oxidizing agent, Au3+ or Ag+?What is a stronger reducing agent, Al or Mg?
p. 262 of LA book
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
Therefore, Eo and free energy (ΔG) should be related.
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
p. 264 of LA book
19.4 Thermodynamics of Redox Reactions
Figure 19.5, p 674
p. 265 of LA book
How is free energy related to work?
How does cell potential relate to free energy?◦ What is n?
What does this mean for spontaneity?
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
What is the standard free energy change (ΔGo) for each of these reactions:
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
p. 265-266 of LA book
19.4 Thermodynamics of Redox Reactions
Figure 19.5, p 674
p. 266 of LA book
How are cell potential and equilibrium related?
What does this mean for spontaneity?
How do we calculate an equilibrium constant given cell potential?
19.4 Thermodynamics of Redox Reactions
Review: All of these redox reactions are spontaneous:
What is the equilibrium constant for each of these reactions:
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
p. 266 of LA book
19.5 The Effect of Concentration on Cell Emf Review: All of these redox reactions are
spontaneous:
What if these are not under standard conditions?
How is cell potential calculated under non-standard conditions?
2+ 2+ o
2+ 2+ o
2+ 2+ o
2+ 2+ o2
Zn s Cu aq Zn aq Cu s 1.10 V
Pb s Cu aq Pb aq Cu s 0.47 V
Zn s Pb aq Zn aq Pb s 0.61 V
Zn s 2H aq Zn aq H g 0.76 V
E
E
E
E
p. 267 of LA book
19.5 The Effect of Concentration on Cell Emf
What will happen to the cell potential if the reactant concentration is less than 1 M (and the product concentration is 1 M)?
What will happen to the cell potential if the product concentration is less than 1 M (and the reactant concentration is 1 M)?
p. 268 of LA book
19.5 The Effect of Concentration on Cell Emf
Practice:What are the cell potentials for these reactions (at 25oC)? Zn(s) | Zn2+ (0.75 M) ǁ Cu2+ (0.0015 M) | Cu(s) Zn(s) | Zn2+ (0.0015 M) ǁ Cu2+ (0.75 M) | Cu(s) Pb(s) | Pb2+ (0.75 M) ǁ Cu2+ (0.0015 M) | Cu(s) Pb(s) | Pb2+ (0.0015 M) ǁ Cu2+ (0.75 M) | Cu(s)
Are these reactions spontaneous (at 25oC)?
p. 268-270 of LA book
19.5 The Effect of Concentration on Cell Emf What is a concentration cell?
A galvanic cell constructed from two half-cells composed of the same material but differing in ion concentrations.◦ What are the oxidation and reduction half
reactions◦ What is Eo
cell?◦ What is the diagram of this cell on the
particle level? Macroscopically?◦ Is this spontaneous? (What would be
measured)?
p. 270-271 of LA book
19.5 The Effect of Concentration on Cell Emf
Practice:What are the cell potentials for these reactions (at 25oC)? Pb(s) | Pb2+ (0.0015 M) ǁ Pb2+ (0.75 M) | Pb(s) Pb(s) | Pb2+ (0.75 M) ǁ Pb2+ (0.0015 M) | Pb(s)
Are these reactions spontaneous (at 25oC)?
p. 271 of LA book
19.6 Batteries
Review: What is a spontaneous redox reaction (or galvanic cell) in terms of:◦ Cell potential◦ Gibbs free energy◦ Equilibrium constant
How would this be useful in designing a stand-alone source of electricity?
What is a battery?A galvanic cell or a series of combined galvanic cells, that can be used as a source of direct electrical current at a constant voltage
p. 273 of LA book
19.6 Batteries What are the half reactions of the lead
storage battery?◦ What happens when the battery is charged?◦ How can the charge on the battery be
monitored?
Figure 19.9, p 681
p. 273-274 of LA book
19.6 Batteries What are fuel cells? What reactions are involved in the fuel
call and what is the standard potential?
Figure 19.11, p 684
p. 274 of LA book
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for many metals in the presence of water or hydrogen ions?
p. 275 of LA book
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for many metals in the presence of water or hydrogen ions?
p. 275 of LA book
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for iron in the presence of hydrogen ions?
p. 276 of LA book
Figure 19.13, p 686
19.7 Corrosion
Review: What is the spontaneous redox reaction (or galvanic cell) for iron in the presence of hydrogen ions?
What does this mean for the protection of iron surfaces?◦ Tin-plated◦ Galvanized◦ Stainless steel
What is a sacrificial electrode?
p. 277 of LA book
Figure 19.15, p 687
19.8 Electrolysis
Review: What indicates a redox reaction that is not spontaneous?
Can a redox reaction that isn’t spontaneous be made spontaneous?
What is electrolysis? What are some specific examples of
electrolysis (keeping in mind the reaction at the anode and cathode)?
p. 277-278 of LA book
19.8 Electrolysis
Figure 19.16, p 688
p. 278 of LA book
19.8 Electrolysis
Figure 19.18, p 689
p. 278-279 of LA book
19.8 Electrolysis
What would happen if these processes were combined?◦ Electrolysis of salt
water (seawater)?
Can we determine how much of a substance is reduced or oxidized?
p. 279 of LA book
Figure 19.19, p 691
19.8 Electrolysis
Practice:What mass of zinc can be plated onto an iron nail (with a mass of 1.565 g) when 355 mA is used for 25 minutes in aqueous zinc chloride?
What is the density of the galvanized nail?
Figure 19.19, p 691
p. 280 of LA book
19.9 Electrometallurgy
Review: What is spontaneous – the reduction of aluminum ions to aluminum metal or the oxidation of aluminum metal to aluminum ions?
How do we refine or prepare aluminum?
Can we use the same principles to refine other metals?
What about purification?
p. 281 of LA book
19.9 Electrometallurgy
Can we use the same principles to refine other metals?
What about purification?
Figure 19.21, p 693
p. 281 of LA book
