Electrochemistry Thermodynamics

Question 1

What reaction occurs at anode and cathode respectively?

Answer 1

Oxidation and Ruduction

Question 2

Compare Anode and Cathode potential in FC

Answer 2

Anode potential is less than cathode potential (for electrons)

Question 3

How to find the cell voltage of a FC?

Answer 3

High cathode potential minus the lower anode potential

Question 4

Half cell reaction for Anode in FC? (For proton conduction membrane aka cation conductor)

Answer 4

H2 —> 2H+ + 2e-

Question 5

Half cell reaction for Cathode in FC? (For proton conduction membrane aka cation conductor)

Answer 5

2H+ + 2e- + 1/2O2 —> H2O

Question 6

Half cell reaction for Anode in electrolysis? (For proton conduction membrane aka cation conductor)

Answer 6

H2O —> 2H+ + 2e- + 1/2O2

Question 7

Half cell reaction for cathode in electrolysis? (For proton conduction membrane aka cation conductor)

Answer 7

2H+ + 2e- —> H2

Question 8

Half cell reaction for Anode in FC? (For oxygen ion conduction membrane aka anion conductor)

Answer 8

O^2- + H2 —> H2O + 2e-

Question 9

Half cell reaction for cathode in FC? (For oxygen ion conduction membrane aka anion conductor)

Answer 9

1/2O2 + 2e- —> O^2-

Question 10

Half cell reaction for cathode in electrolysis? (For oxygen ion conduction membrane aka anion conductor)

Answer 10

H2O + 2e- —> O^2- + H2

Question 11

Half cell reaction for anode in electrolysis? (For oxygen ion conduction membrane aka anion conductor)

Answer 11

O^2- —> 1/2O2 + 2e-

Question 12

Example of oxygen ion conduction membrane?

Answer 12

SOFC

Question 13

Example of proton conduction membrane?

Answer 13

PEFC, PAFC

Question 14

What is the driving force for ionic transportation in electrolysis?

Answer 14

Electrical potential difference

Question 15

What is the driving force for ionic transportation in FC ?

Answer 15

Chemical potential difference

Question 16

Compare Anode and Cathode potential in electrolysis cell

Answer 16

Anode potential is greater than cathode potential and anode is the positive pole like in a galvanic cell

Question 17

What is enthalpy?

Answer 17

The enthalpy is the sum of the system’s internal energy plus the product of its pressure and volume. It can be understood as the total energy available for the reaction.

Question 18

What is gibbs free energy?

Answer 18

The Gibbs free energy considers the entropy losses and hence represents the energy, which can be converted to electricity in the fuel cell reaction, i.e., the usable energy.

Question 19

What is the value for elementary charge constant e?

Answer 19

1,602 10^-19 C

Question 20

What is Avogadro constant N_A?

Answer 20

6,022 10^23 1/mol

Question 21

What is Faraday‘s constant F?

Answer 21

F= e*N_A
= 96485 C/mol

Question 22

What are the equations for Faraday‘s law?

Answer 22

-E°_H = (dH°)/(z*F) ————— Thermoneutral potential in V

-E° = (dG°)/(z*F) ————— Standard potential in V
z= number of e-; F= Faraday‘s constant

Question 23

What is the difference between thermoneutral and standard potential?

Answer 23

Thermoneutral potential is the highest theoretical potential provided whereas standard takes the entropy losses into account.

Question 24

Difference between lower heating value and higher heating value?

Answer 24

Higher heating value (286 kJ/mol) included the released heat of vaporisation. Whether the lower heating value or the higher heating value is to be chosen depends on whether the water produced is assumed to be gaseous or liquid. Gaseous products means lower heating value (252 kJ/mol) and it results in higher cell efficiency.

Question 25

How to calculate the enthalpy of reaction?

Answer 25

∆𝑯 = ∑𝑯𝒑𝒓𝒐𝒅𝒖𝒄𝒕𝒔 - ∑𝑯𝒓𝒆𝒂𝒄𝒕𝒂𝒏𝒕𝒔

Question 26

How to calculate the cell efficiency?

Answer 26

η = ΔG / ΔH

Question 27

How to calculate Gibbs free energy?

Answer 27

dG = dH -TdS (assuming the reaction is isothermal, when not the case - SdT is part of the equation)

Question 28

What is the -dH° in a hydrogen/oxygen reaction, whereby the water generated is assumed to be in the gaseous state?

Answer 28

241,8 kJ/mol

Question 29

What is the -dG° in a hydrogen/oxygen reaction, whereby the water generated is assumed to be in the gaseous state?

Answer 29

228,6 kJ/mol

Question 30

What does the Nernst potential show?

Answer 30

Deviation of the potential from the standard conditions

Question 31

How are the chemical potential and Gibbs free energy related?

Answer 31

dG = Sigma 𝜇_i*dn
AND

dG = Sigma 𝜇_i* 𝜐_i

Question 32

Formula for chemical potential in liquids?

Answer 32

μ_i =μ°_i +RTlna_i
Where a_i is the activity defunded by concentration (c_i) activity coefficient (y_i looking gamma)

Question 33

Formula for chemical potential in ideal gases?

Answer 33

μ_i =μ°_i +RT*ln(p_i/p°)
Where p_i is partial pressure

Question 34

In a reaction bB + cC —> dD + eE how to calculate the equilibrium constant K?

Answer 34

((a_D)^d * (a_E)^e)/((a_B)^b * (a_C)^c): Products/Reactants
So it can be said that K= (big Pi) a_i^ υ_i where υ_i is the stoichiometric factor and negative for reactants

Question 35

How to calculate the dRG for a reaction?

Answer 35

dRG = dRG° + RT ln K where at equilibrium -dRG° = RT ln K

Question 36

What is dRG in a spontaneous and non spontaneous reaction?

Answer 36

dRG < 0 : Spontaneous reaction
dRG > 0 : Non-spontaneous reaction (it is spontaneous in the opposite direction, i.e. favouring reactants)

Question 37

What are the Nernst equations?

Answer 37

E_N = E° - ((RT/z*F) (sigma) υ_i ln a_i)

E_N = E° - ((RT/zF)ln (big Pi) a_i^ υ_i) where υ_i is negative for reactants

Question 38

When is activity a_i = 1?

Answer 38

Activity of solids is 1. In ideal solutions a=1 at 1 mol/liter and for 1 bar partial pressure of a component in gases.

Question 39

What is the equation which shows the dependance of open cell voltage on temperature?

Answer 39

(dE/dT)_P = (dS/z*F)

Question 40

What is the equation which shows the dependance of open cell voltage on pressure?

Answer 40

(dE/dP)_T = -(dV/z*F) where dV is the volume and can be derived with the ideal gas law