4/11/2019 1 52 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 E cell = E red – E ox ● Nernst equation and Common reference electrodes ● Standard and Absolute potentials ● Latimer and Pourbaix diagrams ● Calculating E cell under non-standard state conditions ● Conventions 54 A 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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4/11/2019
1
52
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
4/11/2019
2
55Voltaic pileInvented by Alessandro Volta (1800) but the elements of the pile
(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
4/11/2019
8
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
(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
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
(Accepted) Nomenclature and Terminology that you know, but may have forgotten
4/11/2019
9
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
(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
(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
(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
(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
(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
(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
4/11/2019
12
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)
4/11/2019
13
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
4/11/2019
14
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