Lecture #2 of 17 - University of California, Irvineardo/echem/UCI-CHEM248-2019S... ·...
Transcript of Lecture #2 of 17 - University of California, Irvineardo/echem/UCI-CHEM248-2019S... ·...
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Lecture #2 of 17
53
Looking forward… our review of Chapter “0”
● Cool applications
● Redox half-reactions
● Balancing electrochemical equations
● History of electrochemistry
● IUPAC terminology and Ecell = Ered – Eox
● Nernst equation and Common reference electrodes
● Standard and Absolute potentials
● Latimer and Pourbaix diagrams
● Calculating Ecell under non-standard state conditions
● Conventions
54A Short History Lesson…
Electrochemistry associated with Luigi Galvani who discovered
“animal electricity,” while trying to Frankenstein frogs legs (1791)
Luigi Galvani(1737–1798)
from Wiki
Physician, Physicist, Philosopher
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55Voltaic pileInvented by Alessandro Volta (1800) but the elements of the pile
(galvanic cells) were named after Galvani.
(salt water)
What are the combined half-reactions?
At the Tempio Voltiano (the Volta Temple)
near Volta's home in Como, Italy.
http://en.wikipedia.org/wiki/Voltaic_pile
Alessandro Volta(1745–1827)
from Wiki
Volta presenting his "Voltaic
Pile" to Napoleon and his
court… and now he is a Count!
http://en.wikipedia.org/wiki/Alessandro_Volta
Physicist
56Galvanic Cells
Physically separating the
half-reactions allows the
electrons to go over a
long distance, from the
anode to the cathode via
a (solid) conductor: basis
for conversion of chemical
energy into electricity =
“Electrochemistry” (2019)!
Salt bridge is an ionic conduit to
prevent buildup of charge in both
compartments and also to prevent
bulk mixing of the two solutions
Every non-equilibrium
cell is a galvanic cell (in
one direction, i.e. the
spontaneous direction)
57Electrolysis of water
Volta’s results were shared with
the scientific community and then,
boom, many people demonstrated
electrolysis the same year, and
later, electroplating!
William Cruickshank(17??–1810(1))
Johann Wilhelm Ritter(1776–1810)
Sir Anthony Carlisle(1768–1840)
William Nicholson(1753–1815)
http://en.wikipedia.org/wiki/Johann_Wilhelm_Ritter
Chemist
Chemist Surgeon
Chemist
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58Daniell (galvanic) Cell (1836)
Half-reactions are
physically separated!
anode
oxidation
cathode
reduction
Zn (s) Zn2+ (aq) + 2e– Cu2+ (aq) + 2e– Cu (s)
NET REACTION: Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)
John Frederic Daniell(1790–1845)
from Wiki
No more H2 from the
(primary) battery!
Chemist, Meteorologist
59Voltage Produced by Galvanic Cells
The difference in electric
potential between the anode
and the cathode is called:
Cell potential
Cell voltage
emf (electromotive force)
Cell DiagramZn (s) + Cu2+ (aq) Cu (s) + Zn2+ (aq)
[Cu2+] = 1 M and [Zn2+] = 1 M
Zn (s) | Zn2+ (aq, 1 M) || Cu2+ (aq, 1 M) | Cu (s)
anode cathodesalt bridge
This should be –0.76 V!(we will discuss this soon)
60EXAMPLE: What is the (standard) potential of a galvanic cell
consisting of a Cd electrode in a 1.0 M Cd(NO3)2 solution and a
Cr electrode in a 1.0 M Cr(NO3)3 solution?
Cd2+ (aq) + 2e– Cd (s) E0 = -0.40 V
Cr3+ (aq) + 3e– Cr (s) E0 = -0.74 V
Cd2+ will get reduced to Cd
Cr will get oxidized to Cr3+
… thus, it is reducing
2e– + Cd2+ (1 M) Cd (s)
Cr (s) Cr3+ (1 M) + 3e–Anode (oxidation):
Cathode (reduction):
2Cr (s) + 3Cd2+ (1 M) 3Cd (s) + 2Cr3+ (1 M)
x 2
x 3
E0 = Ecathode – Eanodecell0 0
E0 = -0.40 V – (-0.74 V) cell
E0 = +0.34 V (positive = spontaneous, since ∆𝐺 = −𝑛𝐹𝐸)cell
More negative of the two
Which half-reaction is reducing?
… if your answer is negative then you switched the anode/cathode in the galvanic cell
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61Electrochemistry:
conventions… oh, conventions!
Cathode – electrode where catholyte species are reduced
Anode – electrode where anolyte species are oxidized
62Electrochemistry:
conventions… oh, conventions!
Cathode – electrode where catholyte species are reduced
Anode – electrode where anolyte species are oxidized
Negative/Positive electrode – cathode or anode?… it depends!
For the discharging (galvanic) battery, label the anode and cathode.
http://autoshop101.com/
63Electrochemistry:
conventions… oh, conventions!
Cathode – electrode where catholyte species are reduced
Anode – electrode where anolyte species are oxidized
Negative/Positive electrode – cathode or anode?… it depends!
For the charging (electrolytic) battery, label the anode and cathode.
http://autoshop101.com/
e– e–
anodecathode
This is a generator
(AKA power supply)
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64Electrochemistry:
conventions… oh, conventions!
Positive electrode – positively charged; immersed in the posolyte
Negative electrode – negatively charged; immersed in the negolyte
… Sheesh!
… Take-home message: For batteries, don’t call electrodes
anodes and cathodes (but naming convention used by most is for
discharge)
http://autoshop101.com/
anode
e– e–
cathode
cathodeanode
e– e–
… I’m not kidding!
Zn Cu
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
– –
low impedance to measure current
Zn | Zn2+(aq) || Cu2+(aq) | Cu
IcellJohn Frederic Daniell
(1790–1845)from Wiki
Chemist, Meteorologist
The Daniell Cell (1836)
Zn Cu
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
– –
low impedance to measure current
Zn | Zn2+(aq) || Cu2+(aq) | Cu
Icell
This only works for
less than one second
and then stops due to
Kirchhoff’s current law,
which states that all
current at each location
must sum to zero…
… capacitive charging
The Daniell Cell (1836)
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Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
Zn Cu
– –
Ai+
Bi–
Icell
Now it works =
“electrochemistry”!
Salt bridge
contains an
inert, redox
inactive salt
solution
(electrolyte)
Zn | Zn2+(aq) || Cu2+(aq) | Cu
low impedance to measure current
The Daniell Cell (1836)
Zn Cu
– –
Ai+
Bi–
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
Icell
Zn | Zn2+(aq) || Cu2+(aq) | Cu
low impedance to measure current
* Name this cell type
* Identify anode
* Identify cathode
* Name the
electrode signs
The Daniell Cell (1836)
Zn Cu
– –
Ai+
Bi–
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
Icell
Zn | Zn2+(aq) || Cu2+(aq) | Cu
low impedance to measure current
* Name this cell type
* Identify anode
* Identify cathode
* Name the
electrode signs
* primary galvanic cell
(A/–) (C/+)
The Daniell Cell (1836)
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Zn Cu
– –
Ai+
Bi–
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)
Icell
Zn | Zn2+(aq) || Cu2+(aq) | Cu
low impedance to measure current
The Daniell Cell (1836)
(A/–) (C/+)
This will eventually fully
discharge and reach
equilibrium (ΔG = Ecell = 0)
Then, either direction of
polarization bias results
in electrolytic function
(i.e. charging)!
71PROBLEM TIME!
You try!
(a) What is the standard Ecell for agalvanic cell based on zinc and silver?
(b) If we wanted to electrolyticallycharge the cell from part a (beforeany reactions took place), whatpotential would we have to apply?
72PROBLEM TIME!
You try!
(a) What is the standard Ecell for agalvanic cell based on zinc and silver?
(b) If we wanted to electrolyticallycharge the cell from part a (beforeany reactions took place), whatpotential would we have to apply?
(a) Ecell = +0.80 V – (-0.76 V) = 1.56 V
(b) Ebias < –1.56 V
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73
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑛𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
74
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑛𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
integrate, over timedifferentiate, with respect to time
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
75
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑛𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
E0(Cu2+/0) = +0.34 V vs. SHE
E0(Cu0/2+) = –0.34 V vs. SHE
… is incorrect!
You can subtract redox
potentials but do not change the
sign of the potential and then
call it an oxidation potential!
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
4/11/2019
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76
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑛𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
Based on our current sign convention, it is best
to only write reduction potentials; however, if
we lived in an oxidation-potential-centric world,
we could write them all (i.e. everything) as
oxidation potentials; simply put, it is best to
not mix the conventions and so stick with
reduction potentials
E0(Cu2+/0) = +0.34 V vs. SHE
E0(Cu0/2+) = –0.34 V vs. SHE
… is incorrect!
You can subtract redox
potentials but do not change the
sign of the potential and then
call it an oxidation potential!
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
77
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
78
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝝁, in units of J/mol)
Chemical potential (𝝁, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
Cannot be
measured
independently!
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
4/11/2019
10
79
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
80
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
81
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• Batteries have anodes and cathodes, but these names change depending on if the battery is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative electrode and positive electrode is preferred
International Union of Pure and Applied
Chemistry (IUPAC)
opposites
(Sources: B&F, M3LC course textbook,and http://goldbook.iupac.org/)
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
4/11/2019
11
82International Union of Pure and Applied
Chemistry (IUPAC)
• Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol)
• Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+)
• (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reductionThis relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and…
… partial molar Gibbs free energy is the electrochemical potential ( 𝜇, in units of J/mol)
Chemical potential (𝜇, in units of J/mol)
Galvani/Inner (electric) potential (ϕ, in units of V)
… and in summary, 𝜇 = 𝜇 + 𝑧𝐹ϕAlso, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases)
Also, E = IR (Ohm’s law) when resistance is constant
• Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions
• Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable
• A battery has an anode/anolyte and a cathode/catholyte, but these descriptors change depending on whether the battery is being discharged (galvanic) or charged (electrolytic); negative electrode/negolyte and positive electrode/posolyte are better
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
83
Electrochemical potential of species i in phase β is an energy (J/mol),
𝝁𝒊𝜷=
𝝏𝑮
𝝏𝒏𝒊𝜷
𝑻,𝒑,𝒏𝒋≠𝒊
= 𝝁𝒊𝜷+ 𝒛𝒊𝑭𝝓
𝜷, where
G (Gibbs free energy (J))
ni (amount of species i (mol))
𝝁𝒊 = 𝝁𝒊𝟎 + 𝑹𝑻 𝒍𝒏𝒂𝒊 (chemical potential (J/mol))
zi (valency of species i)
F ≈ 105 (Faraday constant (C/mol)
ϕβ (Galvani/inner electric potential (V))
ai (activity of species i)
For an uncharged species 𝜇𝑖β= 𝜇𝑖
β.
Parsons, Pure & Appl. Chem., 1973, 37, 501
IUPAC Gold (http://goldbook.iupac.org) 83
For “clarity,” a brief (more rigorous) “review” of thermodynamics…
84Half reactions, at non-unity activity, obey the Nernst equation…
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
What is Q?
𝑄 = 𝑝 𝑎𝑝
𝑣𝑝
𝑟 𝑎𝑟𝑣𝑟=
𝑝 γ𝑝𝑐𝑝
𝑐𝑝0
𝑣𝑝
𝑟 γ𝑟𝑐𝑟𝑐𝑟
0
𝑣𝑟 , because 𝜇𝑖 = 𝜇𝑖0 + 𝑅𝑇 ln 𝑎𝑖
𝑄 = 𝑝 𝑐𝑝
𝑣𝑝
𝑟 𝑐𝑟𝑣𝑟
, for dilute solutions… which we never have, and where
ap is the activity of product p
ar is the activity of reactant r
vi is the stoichiometric number of i
γi is the activity coefficient of i
ci is the concentration of i
ci0 is the standard state concentration of i
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85Half reactions, at non-unity activity, obey the Nernst equation…
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
But first… what is Q, again? … the reaction quotient!
𝑄 = 𝑝 𝑎𝑝
𝑣𝑝
𝑟 𝑎𝑟𝑣𝑟=
𝑝 γ𝑝𝑐𝑝
𝑐𝑝0
𝑣𝑝
𝑟 γ𝑟𝑐𝑟𝑐𝑟
0
𝑣𝑟 , because 𝜇𝑖 = 𝜇𝑖0 + 𝑅𝑇 ln 𝑎𝑖
𝑄 = 𝑝 𝑐𝑝
𝑣𝑝
𝑟 𝑐𝑟𝑣𝑟
, for dilute solutions… which we never have, and where
ap is the activity of product p
ar is the activity of reactant r
vi is the stoichiometric number of i
γi is the activity coefficient of i
ci is the concentration of i
ci0 is the standard state concentration of i
86Half reactions, at non-unity activity, obey the Nernst equation…
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
But first… what is Q, again? … the reaction quotient!
𝑄 = 𝑝 𝑎𝑝
𝑣𝑝
𝑟 𝑎𝑟𝑣𝑟=
𝑝 γ𝑝𝑐𝑝
𝑐𝑝0
𝑣𝑝
𝑟 γ𝑟𝑐𝑟𝑐𝑟
0
𝑣𝑟 , because fundamentally 𝜇𝑖 = 𝜇𝑖0 + 𝑅𝑇 ln 𝑎𝑖
𝑄 = 𝑝 𝑐𝑝
𝑣𝑝
𝑟 𝑐𝑟𝑣𝑟
, for dilute solutions… which we never have!
ap is the activity of product p
ar is the activity of reactant r
vi is the stoichiometric number of i
γi is the activity coefficient of i
ci is the concentration of i
ci0 is the standard state concentration of i
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
−𝑛𝐹𝐸 = −𝑛𝐹𝐸0 + 𝑅𝑇 ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹ln𝑄
87Half reactions, at non-unity activity, obey the Nernst equation…
Reaction quotient as
product and quotient of
species’ activities
from Wiki
Physicist
Walther Hermann Nernst
(1864–1941)
Nobel Prize (Chemistry, 1920)
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Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
−𝑛𝐹𝐸 = −𝑛𝐹𝐸0 + 𝑅𝑇 ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹
log𝑄
log 𝑒
𝐸 = 𝐸0 −𝑅𝑇
0.4343𝑛𝐹log𝑄
𝐸 = 𝐸0 −2.3026𝑅𝑇
𝑛𝐹log 𝑄
88Half reactions, at non-unity activity, obey the Nernst equation…
Reaction quotient as
product and quotient of
species’ activities
from Wiki
Physicist
Walther Hermann Nernst
(1864–1941)
Nobel Prize (Chemistry, 1920)
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
−𝑛𝐹𝐸 = −𝑛𝐹𝐸0 + 𝑅𝑇 ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹
log𝑄
log 𝑒
𝐸 = 𝐸0 −𝑅𝑇
0.4343𝑛𝐹log𝑄
𝐸 = 𝐸0 −2.3026𝑅𝑇
𝑛𝐹log𝑄
… and at 298.15 K, 𝐸 = 𝐸0 −0.05916 V
𝑛log𝑄
89Half reactions, at non-unity activity, obey the Nernst equation…
Reaction quotient as
product and quotient of
species’ activities
from Wiki
Physicist
Walther Hermann Nernst
(1864–1941)
Nobel Prize (Chemistry, 1920)
Take ∆𝐺 = ∆𝐺0 + 𝑅𝑇 ln𝑄 and use the relation ∆𝐺 = −𝑛𝐹𝐸,
−𝑛𝐹𝐸 = −𝑛𝐹𝐸0 + 𝑅𝑇 ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹ln𝑄
𝐸 = 𝐸0 −𝑅𝑇
𝑛𝐹
log𝑄
log 𝑒
𝐸 = 𝐸0 −𝑅𝑇
0.4343𝑛𝐹log 𝑄
𝐸 = 𝐸0 −2.3026𝑅𝑇
𝑛𝐹log𝑄
… and at 298.15 K, 𝐸 = 𝐸0 −0.05916 V
𝑛log𝑄
90Half reactions, at non-unity activity, obey the Nernst equation…
Memorize ~60 mV per order in log10, but do not forget n and that this is at 25 °C!
from Wiki
Physicist
Walther Hermann Nernst
(1864–1941)
Nobel Prize (Chemistry, 1920)
Reaction quotient as
product and quotient of
species’ activities
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91
standard (SHE)
Rigorously, each needs
to be divided by the
standard-state condition
92
Thus, the potentials for half-cell reactions are actually
full-cell potential (difference(s)) versus SHE, or other!
standard (SHE)
93
standard (SHE)
* Normal hydrogen electrode (NHE) is an empirical SHE ([H+] = 1; not standard state)* Standard hydrogen electrode (SHE) is a hypothetical, perfect NHE (a = 1; not empirical)* Reversible hydrogen electrode (RHE) is the SHE but the same regardless of pH* And generally, formal potentials (E0’) take into consideration non-idealities and changesin ionic strengths so that the reaction quotient only has concentrations, and not activities
Ramette, J. Chem. Educ., 1987, 64, 885
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94
Potential Standard Potential
* Normal hydrogen electrode (NHE) is an empirical SHE ([H+] = 1; not standard state)* Standard hydrogen electrode (SHE) is a hypothetical, perfect NHE (a = 1; not empirical)* Reversible hydrogen electrode (RHE) is the SHE but the same regardless of pH* And generally, formal potentials (E0’) take into consideration non-idealities and changesin ionic strengths so that the reaction quotient only has concentrations, and not activities
standard (SHE)
Ramette, J. Chem. Educ., 1987, 64, 885
95
Potential Standard Potential
standard (SHE)
Given this value, what
is this experimental
redox potential versus?
96
vs. SHE
Potential Standard Potential
standard (SHE)
Given this value, what
is this experimental
redox potential versus?
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97
Look up half-reactions and standard reduction potentials in an
Electrochemical Series table (CRC, B&F Appendix C, WWW):
Anode: E0anode = -0.76 V
Cathode: E0cathode = +1.51 V
Note: Although strictly correct, do not use “–E0” as the “E0 for oxidation”
Note: Be careful to choose the correct half-reaction with MnO4–
Zn Zn2+ + 2e–
MnO4– + 8H+ + 5e– Mn2+ + 4H2O
EXAMPLE: Write a balanced chemical equation and
calculate the standard cell potential for the galvanic cell:
Zn(s) | Zn2+ (1 M) || MnO4– (1 M), Mn2+ (1 M), H+ (1 M) | Pt(s)
98CRC Handbook of Chemistry and Physics, 92nd Edition
http://folk.ntnu.no/andersty/2.%20Klasse/KJ1042%20Termodynamikk%20med%20lab/Lab/
Oppgave%205%20-%20Standard%20reduksjonspotensial/Rapportfiler/E0.pdf
* All values versus SHE
MnO4– + 8H+ + 5e–
Mn2+ + 4H2O
Zn Zn2+ + 2e–
99
Anode: E0anode = -0.76 V
Cathode: E0cathode = +1.51 V
Note: Although strictly correct, do not use “–E0” as the “E0 for oxidation”
Note: Be careful to choose the correct half-reaction with MnO4–
To get the balanced overall reaction… ?
Zn Zn2+ + 2e–
MnO4– + 8H+ + 5e– Mn2+ + 4H2O
EXAMPLE: Write a balanced chemical equation and
calculate the standard cell potential for the galvanic cell:
Zn(s) | Zn2+ (1 M) || MnO4– (1 M), Mn2+ (1 M), H+ (1 M) | Pt(s)
Look up half-reactions and standard reduction potentials in an
Electrochemical Series table (CRC, B&F Appendix C, WWW):
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100
Anode: E0anode = -0.76 V
Cathode: E0cathode = +1.51 V
Note: Although strictly correct, do not use “–E0” as the “E0 for oxidation”
Note: Be careful to choose the correct half-reaction with MnO4–
To get the balanced overall reaction, multiply the anode
reaction by 5 and add to 2 times the cathode reaction, giving:
Ecell = E0cathode – E0
anode = 1.51 V + 0.76 V = +2.27 V
Zn Zn2+ + 2e–
MnO4– + 8H+ + 5e– Mn2+ + 4H2O
2MnO4– (aq) + 16H+ (aq) + 5Zn (s) 5Zn2+ (aq) + 2Mn2+ (aq) + 8H2O (l)
EXAMPLE: Write a balanced chemical equation and
calculate the standard cell potential for the galvanic cell:
Zn(s) | Zn2+ (1 M) || MnO4– (1 M), Mn2+ (1 M), H+ (1 M) | Pt(s)
Look up half-reactions and standard reduction potentials in an
Electrochemical Series table (CRC, B&F Appendix C, WWW):
101
* All values versus SHE
CRC Handbook of Chemistry and Physics, 92nd Edition
http://folk.ntnu.no/andersty/2.%20Klasse/KJ1042%20Termodynamikk%20med%20lab/Lab/
Oppgave%205%20-%20Standard%20reduksjonspotensial/Rapportfiler/E0.pdf
Q: What processes occur in electrochemistry? … one more …
(remember this?)
* How negative can Eo be?
102
Example: solvated electrons
Q: What processes occur in electrochemistry? … one more …
A: Winter, 2017: Those involving the motion/transport of charge –
carried by entities other than unsolvated electrons and holes –
through phase(s), or the transfer of charge across interface(s).
Prof. Robert Hamers (Univ. of Wisconsin)
http://hamers.chem.wisc.edu/people
Zhu, …, Hamers, Nature Materials, 2013, 12, 836
diamond
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103First description of conductivity using solvated electrons
Cady, J. Phys. Chem., 1897, 1, 707
During the first part of the twentieth century, E. C. Franklin and C. A. Kraus probably did more to elucidate the chemistry of
liquid ammonia solutions than everybody else combined… It is perhaps little known that their work was prompted by the
research and insight of H. P. Cady, carried out while he was an undergraduate! Whilst working on cobalt ammine
complexes, Cady proposed that ammonia in these (and other “double salts”) must function in a manner akin to water in salts
with water of crystallization. He suggested further that liquid ammonia would probably be found to resemble water in its
physical and chemical properties—thus adding a second to our list of ionizing solvents. Cady’s undergraduate work, carried
out without supervision, published in 1897, was perhaps the first physical chemistry study of liquid ammonia solutions.
Zurek, Edwards, & Hoffman, Angew. Chem. Int. Ed., 2009, 48, 8198
104
Example: solvated electrons
Q: What is electrochemistry? … one more …
A: Any process involving the motion/transport of charge – carried
by entities other than unsolvated electrons and holes – through
phase(s), or the transfer of charge across interface(s).
Prof. Robert Hamers (Univ. of Wisconsin)
http://hamers.chem.wisc.edu/people
Zhu, …, Hamers, Nature Materials, 2013, 12, 836
What is this?
diamond
105Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Pure & Appl. Chem., 1986, 58, 955
Prof. Sergio Trasatti
(Università de Milano, Italy)
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106Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Pure & Appl. Chem., 1986, 58, 955
FOR YOUR REFERENCE
107Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
FOR YOUR REFERENCE
108Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
… but we need an electrode!
FOR YOUR REFERENCE
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109Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
… but we need an electrode!
FOR YOUR REFERENCE
110Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955… but we need an electrode!
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
FOR YOUR REFERENCE
111Absolute potentials can be measured / approximated…
very carefully…
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955… but we need an electrode!
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
FOR YOUR REFERENCE
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112Absolute potentials can be measured / approximated…
very carefully…
Farrell and McTigue, Electroanal. Chem. Interfac. Electrochem., 1982, 139, 37
Trasatti, Electroanal. Chem. Interfac. Electrochem., 1974, 52, 313
Trasatti, Pure & Appl. Chem., 1986, 58, 955
Born–Haber cycle:
e(Hg)
𝜇𝑒𝐻𝑔
… but we need an electrode!
Hg
Pt
FOR YOUR REFERENCE