THE VOLTAIC (GALVANIC) ELECTROCHEMICAL CELL. 4/26

1
THE VOLTAIC (GALVANIC) ELECTROCHEMICAL CELL. 4/26

• OBJECTIVES
• USING STANDARD REDUCTION POTENTIALS TO PREDICT
  CELL STANDARD VOLTAGE (E0) AND SPONTANEITY.
• CALCULATING WORK POTENTIAL OF A VOLTAIC CELL.
• USING THE NERNST EQUATION TO FIND NONSTANDARD
  VOLTAGE.
• CALCULATING ?G RT Ln K
• CALCULATING MOLES FROM APPLIED CURRENT.
• CALCULATING CURRENT FROM MOLES REACTED.
• CONSTRUCTING THE CELL COMPONENTS FROM THEORY AND
  LOGIC.

2

• OBJECTIVE
• USING STANDARD REDUCTION POTENTIALS TO PREDICT
  CELL STANDARD VOLTAGE (E0) AND SPONTANEITY.
• YOU NEED VOLTAGES FROM REDUCTION POTENTIAL TABLES
  FOR EACH HALF REACTION.
• REVERSE THE REDUCTION THAT HAS THE LOWEST
  VOLTAGE, THAT IS YOUR OXIDATION ( THE HIGHER
  VOLTAGE IS THE HIGHER REDUCTION POTENTIAL)
• BALANCE HALF REACTIONS AS USUAL, HOWEVER, NEVER
  MULTIPLY VOLTAGES.
• CALCULATE EO USING
• EOCELL EOREDUCTION EOOXIDATION

3

• OBJECTIVE
• USING STANDARD REDUCTION POTENTIAL, PREDICT CELL
  STANDARD VOLTAGE (E0) AND SPONTANEITY FOR
• Zn(S)/Zn2Cu2/Cu(S)
• EOCELL EOREDUCTION EOOXIDATION
• GIVEN FROM REDUCTION POTENTIAL TABLES
• Cu2 2e- ??Cu0(S) EO 0.34 V
• Zn2 2e- ??Zn0(S) EO -0.76 V

4

• OBJECTIVE
• USING STANDARD REDUCTION POTENTIAL, PREDICT CELL
  STANDARD VOLTAGE (E0) AND SPONTANEITY FOR
• Zn(S)/Zn2Cu2/Cu(S)
• GIVEN FROM REDUCTION POTENTIAL TABLES
• Cu2 2e- ??Cu0(S) EO 0.34 V
• Zn2 2e- ??Zn0(S) EO -0.76 V
• EOCELL EOREDUCTION EOOXIDATION
• E0CELL (0.34V) (-0.76V) 1.10V

THE CELL POTENTIAL OF THIS CELL IS POSITIVE,
WHICH MEANS THE CELL IS SPONTANEOUS AND ?G IS
NEGATIVE..
5

• OBJECTIVE
• USING STANDARD REDUCTION POTENTIAL, PREDICT CELL
  STANDARD VOLTAGE (E0) AND SPONTANEITY FOR
• Zn(S)/Zn2Cu2/Cu(S)
• GIVEN FROM REDUCTION POTENTIAL TABLES
• Cu2 2e- ??Cu0(S) EO 0.34 V
• Zn0(S) ?? Zn2 2e- EO 0.76 V
• Zn0(S) Cu2 ? Cu0(s) Zn2 EO 1.10 V

THE REDUCTION POTENTIAL OF THE ZINC ION IS LOWER
THAN COPPER THE ZINC HALF REACTION MUST BE
REVERSED AND THE SIGN OF ITS VOLTAGE RECIPROCATED.
6

• OBJECTIVE
• CALCULATING WORK and ?G OF THE CELL
• Zn(S)/Zn2Cu2/Cu(S)
• GIVEN FROM REDUCTION POTENTIAL TABLES
• Cu2 2e- ??Cu0(S) EO 0.34 V
• Zn0(S) ?? Zn2 2e- EO 0.76 V
• Zn0(S) Cu2 ? Cu0(s) Zn2 EO 1.10 V
• ?G 2.303 RT Log K
• OR
• wMAX nFE0 and (?G - wMAX)
• wMAX (2mol e-) (96,500 C/mol e-)(1.10 V)
• wMAX 212,000 J 212 kJ
• ?G -212 kJ

7

• OBJECTIVE
• CALCULATING NON-STANDARD E WITH THE NERNST
  EQUATION FOR
• Zn(S)/Zn2Cu2/Cu(S)
• Zn0(S) Cu2 ? Cu0(s) Zn2 EO 1.10 V

NON-STANDARD IS MOLARITIES OTHER THAN 1.0 AND
TEMPERARES OTHER THAN 25OC
ENONSTANDARD EO 0.0592 V (LOG Q)
n
(
)
ENONSTANDARD EO 0.0592 V LOG Zn2
n
Cu2
ENONSTANDARD EO 0.0592 V LOG Zn2
n
Cu2
(
)
NOTE ? values of the voltages and n, you can
use the Nernst equation to solve for Q or
molarities of ions.
8
ENONSTANDARD 0.0296 V (1.30) 1.06 V

• IF THE MOLARITIES ARE 1.O MOLAR
• (OR P 1 atm) FOR ALL SPECIES, Q 1 AND E0 E.
• 2. E RARLEY EO DUE TO INEFFICIENCY, BACK
  VOLTAGE AND RESISTANCE IN THE CELL

9

• OBJECTIVE CALCULATING ?G RT Ln K OR (?G
  2.303 RT Log K)
• FOR THE CELL Zn(S)/Zn2Cu2 /Cu(S)
• ?G 2.303 RT Log K -nFEo
• Log Kc nEo
• 0.0592 V