ElectrochemistryG =

Electrical work

w =

n =

wmax

# moles e-

F = charge on 1 mol e-

=electrical potential

- n F wmax = H - TS

Electrochemistry

electrons

ose lectronsxidation

ain lectronseduction

reduction oxidation

LEO

GER Ger

Electrochemistry

silver Ag(s)

aluminum Al(s)

Ag(s)

Al(s)

these are reactions

G =

Gof =

a) oxidationb) reduction

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-

a) oxidationb) reduction

reduction

K+ Cl-

anode cathode

1 mol Al3+ + 3 mol NO3-

1 molecule Al3+

1M AgNO31M Al(NO3)3

AgAl

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

3e-

a) oxidationb) reduction

reduction

K+ Cl-

anode cathode

1 mol Al3+ + 3 mol NO3-

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)

F2 is spontaneously

Li is spontaneously

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

reduced

oxidized Li is a agentreducing

a) oxidizingb) reducing

F2 is an agent

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: Ag+ + e- Agoxidation reaction: Al Al3+ + 3e-

0.80 1.66

o (V)

a)

b)

3( )

o is intensive

_____________ ____3Ag+ o

cell =+Al 3Ag +Al3+ 2.46 V

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

Balancing redox reactions

Cr2O72- (aq)

balance O

balance H

balance charge

balance Cr

Cr2O72- Cr3+ 2

add H2O

+ H2O 7

add H+

H++14

add e-

e-+ 6

Cr3+ (aq)

Cr2O72- + 14 H+ + 6 e- 2 Cr3+ + 7 H2O

oxidation or reduction

oxidation state of Cr

O = 2-

Cr2O72- Cr3+

Cr has been

Cr is an agent

6+ 3+

reduced

oxidizing

Cr2O72- + 14 H+ + 6 e- 2 Cr3+ + 7 H2O

oxidation or reduction

GER gain e- reduction

need oxidation reaction

2H+ (aq) H2(g)

balance charge with e-

2H+ + 2e- H2(g)

another reduction reaction

H2(g) 2H+ (aq) + 2e-( )3