Equations

Question 1

What are the SI units of electrochemistry?

Answer 1

• Electric charge: coloumb C.
• Electric current (I): amps A (1A = 1Cs-1)
• Potenital difference: volts V (V = I x R)

Question 2

How do we use standard reduction potentials? (Equations).

Answer 2

RHS Cathode:
Aox + ne- –> Ared
Eo (Aox/Ared)

LHS Anode:
Bred –> Box + ne-
Eo = -Eo (Box/Bred)

Overall: RHS - LHS
Eo(cell): Eo(Aox/Ared) - Eo(Box/Bred)

Question 3

Outline the reactions in a H2 fuel cell.

Answer 3

Anode: H2 –> 2H+ + 2e-
Cathode: 1/2O2 + 2H+ +2e- –> H2O
Overall: 2H2 + O2 –> 2H2O

Question 4

State the equation for gibbs free energy change (∆G) and annotate.

Answer 4

∆G = -nFE

n: number of electrons transferred
F: Faraday constant
E: standard cell potential

Question 5

State the equation that combines standard cell potential + equilibrium constant.

What values for this equation favour products/reactants?

Answer 5

lnK = nF/RT Eocell

Products: E > 0, lnK > 0, K > 1

Reactants: E < 0, lnK < 0, K < 1

Question 6

State the Nernst equation and annotate.

Answer 6

Ecell = Eocell - RT/nF lnQ

Ecell: cell potential
Eocell: standard cell potential
R: ideal gas constant
T: temperature in K
n: number moles of electrons
F: Faraday constant
Q: reaction quotient

Question 7

State the equation used when identifying changes in Eo/Gibbs free energy.

Answer 7

∆S = nF (E’ - E)/T’ - T