Equlibria at electrodes

Question 1

How does the energy of the electrons in the Pt electrode and energy of the solution reach equilibrium?

Answer 1

The homo of the Solution species transfers electrons to the platnum electrode until the energy of the electrons of the Pt electrode match the energy of electons of the HOMO of the solution species

Question 2

The number of electrons required to achieve equilibrium depends on what?

Answer 2

The relative initial energies of the solution redox species and the electrons in the Pt electrode

Question 3

why is the electrode potential for Ru(NH3)6
3+/2+ more negative than Fe(CN)6
4-/3-?

Answer 3

The HOMO of Ru(NH3)6
3+/2+ is of higher energy than Fe(CN)6
4-/3- , so more electrons are needed to transfer to the electrode to reach equilibrium

Question 4

What’s the Nernst equation?

Answer 4

𝐸 = 𝐸𝑜 +𝑅𝑇/𝑛𝐹 * ln[𝑂]/[𝑅]

E = Measure electrode potential
E𝑜 = Electrode potential of species

Question 5

What is the Nernst Equation for the reaction: Cu2+ + 2e- ↔ Cu

Answer 5

E = E𝑜 +RT/2F*ln[Cu2+]/[Cu]

n = 2 as there are 2 electrons involved in the reacion

Question 6

What is the measured electrode potential when [Cu2+] = 1 M, 0.1 M and 0.01 M?
Assume E𝑜 = 0.34 V

Answer 6

E1 = 0.34 V (Because ln 1 = 0)
E2 = 0.34 + (8.314*298)/(2*96485)*ln(0.1) = 0.31 V
E3 = 0.34 + (8.314*298)/(2*96485)*ln(0.01) = 0.28 V

Question 7

What is the measured electrode potential when [A3+] = 1M, 0.1 M and 0.01 M
Assume E𝑜 = 1.6 V

Answer 7

E1 = 1.6 V (Because ln 1 = 0)
E2 = 1.6 + (8.314*298)/(3*96485)*ln(0.1) = 1.58 V
E3 = 0.34 + (8.314*298)/(3*96485)*ln(0.01) = 1.56 V

Question 8

What is the Fermi level EF? and where is the conduction band in Pt? And why does it have metallic conductivity?

Answer 8

The fermi level is the average energy level of the available electrons in a metal.
The conduction band is formed by the overlap of the 6s 6p and 5d bands. The conduction band is partly filled with electrons, so it has metallic conductivity

Question 9

At 0 K, there is a sharp cutoff between the lower occupied levels and the higher empty levels, what is the fermi level here?

Answer 9

The fermi level or the fermi energy is the top filled level of the band at 0 K

Question 10

Some electrons can be thermally excited above the fermi level, which electrons are avvailable for excitation?

Answer 10

The electrons in partly filled energy levels and the electrons that are just above and below the fermi level

Question 11

if the HOMO of a species is higher than the fermi level of the platinum electrode, how does the fermi level increase to reach equilibrium?

Answer 11

the electrons in the HOMO of the species will transfer electrons to the fermi level of the platnum, raising the fermi level to the level of the HOMO of the species

Question 12

how can the equilibrium of the fermi level be pertrubed?

Answer 12

By applying external voltages to the electrode usualy by connecting it to a battery or an instrument called a potentiostat

Question 13

When a negative electrode potential is applied to the equilibrium of a Pt electrode and a solution with Fe(CN)6
3- and Fe(CN)6
4- ions, what will happen?

Answer 13

Electrons from the Pt electrode will move to the LUMO of the solution which is the Fe(CN)6
3-. This will cause the reduction of Fe(CN)6
3- to Fe(CN)6
4-. The reduction current will flow: Fe(CN)6
3- + e- → Fe(CN)6
4-

Question 14

When a positive electrode potential is applied to the equilibrium of a Pt electrode and a solution with Fe(CN)6
3- and Fe(CN)6
4-

Answer 14

Electrons from the HOMO of the solution which is the electrons from Fe(CN)6
4- go to the Pt electrode, which cause the oxidation of Fe(CN)6
4- to Fe(CN)6
3-. The oxidation current will flow: Fe(CN)6
4- - e- → Fe(CN)6
3-

Question 15

What is the measured electrode potential when [A2+] = .6M, 0.4 M and 0.2 M
Assume E𝑜 = 1.4 V

Answer 15

E1 = 1.4 + (8.314*298)/(2*96485)*ln(0.6) = 1.396 V
E2 = 1.4 + (8.314*298)/(2*96485)*ln(0.4) = 1.392 V
E3 = 1.4 + (8.314*298)/(2*96485)*ln(0.2) = 1.386 V