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.

OBJECTIVE: EOCELL = EOREDUCTION – EOOXIDATION 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

Zn(S)/Zn2+||Cu2+/Cu(S) OBJECTIVE: 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

Zn(S)/Zn2+||Cu2+/Cu(S) OBJECTIVE: 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..

Zn(S)/Zn2+||Cu2+/Cu(S) OBJECTIVE: 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.

∆G = –2.303 RT Log K wMAX = nFE0 : and (∆G = - wMAX) OBJECTIVE: 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: Zn(S)/Zn2+||Cu2+/Cu(S) 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 [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.

( ) ( ) ENONSTANDARD = EO – 0.0592 V (LOG Q) n ENONSTANDARD = EO – 0.0592 V * LOG [Zn2+] n [Cu2+] ( ) ENONSTANDARD = EO – 0.0592 V * LOG (0.40) n (0.020) ( ) 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

FOR THE CELL : Zn(S)/Zn2+||Cu2 /Cu(S) 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