Electrochemistry

Mechanical work

G =

Electrical work

w =

n =

w =

wmax

# moles e-

F = charge on 1 mol e-

=electrical potential

- Pext V - n F

Electrochemistry

electrons

ose lectronsxidation

ain lectronseduction

reduction oxidation

LEO

GER Ger

Electrochemistry

silver Ag(s)

aluminum Al(s)

Ag(s)

Al(s)

G =

Gof =

Ag+(aq)

Al3+(aq)

77 kJ mol-1

-481 kJ mol-1

Ag+(aq) + e-of

Al3+(aq) + 3e-

Ag(s) Ag+(aq) + e-

Al(s) Al3+(aq) + 3e-

Gof = 77 kJ mol-1

Gof = -481 kJ mol-1

Al(s) Al3+(aq) + 3e- Gof = -481 kJ mol-1

Ag+(aq) + e- Ag(s) Go = -77 kJ mol-13( ) 3( )__________________ ________________

3Ag+ Go =

spontaneous

+ Al 3Ag + Al3+ -712 kJ/mol

1 molecule Al3+

3Ag++ Al Al3+ + 3Ag

1M AgNO31M Al(NO3)3

AgAl

Ag+ + e- AgAl Al3+ + 3e-

3e-

oxidation reduction

K+ Cl-

anode cathode

1 mol Al3+ + 3 mol NO3-

1M AgNO31M Al(NO3)3

AgAlK+ Cl-

anode cathode

Ag+ +e- AgAl Al3+ + 3e-

oxidation reduction

Al(s)Al3+(1 M)Ag+(1 M)Ag(s)

Reduction Potential

Al(s) Al3+(aq) (1M) Ag+(aq) (1M) Ag(s)

3Ag+ + Al 3Ag + Al3+

Go =

o =

Go = -712 kJ/mol

wmax =

Al(s) Al3+ + 3e- Ag+ + e- Ag

standard reduction potentialstandard = 1M, 1 atmreduction potential = tendency to gain e-

wmax-n F o

half-reaction o (V)

o = 0 Standard Hydrogenelectrode

spontaneous reduction

spontaneous oxidation

(SHE)

F2 + 2e- 2F- 2.87Ag+ + e- Ag 0.80

Cu2+ + 2e- Cu 0.342H+ + 2e- H2 0.00Sn2+ + 2e- Sn -0.13

Li+ + e- Li -3.05Al3+ + 3e- Al -1.66

half-reaction o (V)F2 + 2e- 2F- 2.87Ag+ + e- Ag 0.80Cu2+ + 2e- Cu 0.342H+ + 2e- H2 0.00Sn2+ + 2e- Sn -0.13Al3+ + 3e- Al -1.66Li+ + e- Li -3.05

Al half-cell and Ag half-cell

reduction reaction: oxidation reaction:

ocell

ocell = o

red - oox

Ag+ (aq) + e- Ag(s)

Al3+ (aq) + 3e- Al(s)

o = 0.80 V

o = -1.66 V

ocell = 0.80 - (-1.66) = 2.46 V

ocell > 0

ocell < 0

voltaic or galvanic cell spontaneous

electrolytic cell non-spontaneous

Electrochemical work

3Ag+ + Al 3Ag + Al3+ ocell = 2.46 V

Go = wmax = -n = mol of e-

Go =

= -712170 CV

n

F = faraday = 96,500 C / mol e-

F

o = standard reduction potential V (J/C)

o

-(3 mol e-) (96,500 C/mol e-)(2.46V)

= -712170 J = -712 kJ

= -712 kJGo = wmax = -nFo = -RT ln K

Equilibrium constant, K

ln K = -712 kJ- RT

K = e287

= - nFo

- 8.314x10-3 x 298

= 287