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THE VOLTAIC (GALVANIC) ELECTROCHEMICAL CELL. 4/26. OBJECTIVES: USING STANDARD REDUCTION POTENTIALS TO PREDICT CELL STANDARD VOLTAGE ( E 0 ) AND SPONTANEITY. CALCULATING WORK POTENTIAL OF A VOLTAIC CELL. USING THE NERNST EQUATION TO FIND NONSTANDARD VOLTAGE. CALCULATING ∆G = –RT Ln K
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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: • 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: • 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: • 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: • 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 = +1.10V 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: • 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 = +1.10V • ∆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: • CALCULATING NON-STANDARD E WITH THE NERNST EQUATION FOR: • Zn(S)/Zn2+||Cu2+/Cu(S) • Zn0(S) + Cu2+ Cu0(s) + Zn2+ EO = +1.10V 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
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 • 0.0592V
