Transcript galvanicAP.ppt

THE VOLTAIC (GALVANIC) ELECTROCHEMICAL
CELL. 4/26
OBJECTIVES:
1. USING STANDARD REDUCTION POTENTIALS
TO PREDICT CELL STANDARD VOLTAGE (E0)
AND SPONTANEITY.
2. CALCULATING WORK POTENTIAL OF A
VOLTAIC CELL.
3. USING THE NERNST EQUATION TO FIND
NONSTANDARD VOLTAGE.
4. CALCULATING ∆G = –RT Ln K
5. CALCULATING MOLES FROM APPLIED
CURRENT.
6. CALCULATING CURRENT FROM MOLES
REACTED.
7. CONSTRUCTING THE CELL COMPONENTS
FROM THEORY AND LOGIC.
OBJECTIVE:
1. 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
OBJECTIVE:
1. USING STANDARD REDUCTION POTENTIAL,
PREDICT CELL STANDARD VOLTAGE (E0)
AND SPONTANEITY FOR
Zn(S)/Zn2+||Cu2+/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
OBJECTIVE:
1. USING STANDARD REDUCTION POTENTIAL,
PREDICT CELL STANDARD VOLTAGE (E0)
AND SPONTANEITY FOR
Zn(S)/Zn2+||Cu2+/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..
OBJECTIVE:
1. USING STANDARD REDUCTION POTENTIAL,
PREDICT CELL STANDARD VOLTAGE (E0) AND
SPONTANEITY FOR
Zn(S)/Zn2+||Cu2+/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.
OBJECTIVE:
1. CALCULATING WORK and ∆G OF THE CELL:
Zn(S)/Zn2+||Cu2+/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
OBJECTIVE:
1. CALCULATING NON-STANDARD E WITH THE
NERNST EQUATION FOR:
Zn(S)/Zn2+||Cu2+/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
n
ENONSTANDARD = EO – 0.0592 V * LOG
n
NOTE ♫ : values of the voltages and n,
you can use the Nernst equation to solve
for Q or molarities of ions.
[Zn2+]
[Cu2+]
)
[Zn2+]
[Cu2+]
)
(
(
ENONSTANDARD = EO – 0.0592 V (LOG Q)
n
ENONSTANDARD = EO – 0.0592 V * LOG
n
ENONSTANDARD = EO – 0.0592 V * LOG
n
[Zn2+]
[Cu2+]
(
)
(0.40)
(0.020)
(
ENONSTANDARD = 0.0296 V (1.30) = 1.06 V
1. 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
)
1. OBJECTIVE CALCULATING ∆G = –RT Ln K OR
(∆G = –2.303 RT Log K)
FOR THE CELL : Zn(S)/Zn2+||Cu2 /Cu(S)
∆G = –2.303 RT Log K =-nFEo
Log Kc =
nEo
0.0592 V