Lecture 25 3/28/07

Secondary Batteries (rechargeable)NiCad

E° = 1.229 V

Cathode: 2NiO(OH) (s) + 2H2O + 2e- 2Ni(OH)2 (s) +

2OH- Anode: Cd(s) + 2OH- - Cd(OH)2 (s) + 2e-

Secondary Batteries (rechargeable)NiMH

E° = 1.4 V

Cathode: NiO(OH) (s) + H2O + e- Ni(OH)2 (s) + OH-

Anode: MH(s) + OH- - M (s) + H2O + e-

H2 (g) + 2 AgCl (s) 2H+ (aq) + 2 Cl- (aq) + 2Ag(s)

This reaction occurs in a cell with H2 (g) pressure of 1.0 atm and [Cl-] = 1.0 M at 25˚C; the measured Ecell = 0.34 V. What is the pH of the solution?

E˚(cathode) = 0.222V

Ecell = 0.01V for a galvanic cell with this reaction at 25˚C.

Sn(s) + Pb2+ (aq) Sn2+ (aq) + Pb(s)

What is the equilibrium constant for the reaction?

Electrolysis of molten salts

Cathode: 2Na+ (l) + 2e- 2Na(l) E° = -2.71 V

Anode:2Cl- (l) Cl2 (g) + 2e- E° = 1.36 V

Net: 2NaCl (l) Cl2 (g) + 2Na(l) E° =

Electrolysis of aqueous solutions

What would happen if you put electricity into a solution of KI?

Possible oxidation reactions?

Possible reduction reactions?

Actual Reaction?

General rules in aqueous solutions

Reduction 6H2O + 2e- H2 (g) + 2OH- E° = -0.8277 V

Oxidation 6H2O O2 (g) + 4H3O+ + 4e- E° =

1.229 V

Counting electrons

Mass timeand C/sec)or (A Current

timeand C/sec)or (A Current Mass

1.50 amps flow through a Ag+(aq) solution for 15.0 min.

What mass of Ag metal is deposited?

The anode reaction in a lead storage battery is:

Pb(s) + HSO4-(aq) PbSO4(s) + H+(aq) + 2e-

If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last?

Recap

Balancing Redox reactions Electrochemical cells Batteries Standard Reduction Potential table

Corrosion Nernst equation Electrolysis

Molten aqueous

Counting electrons

Acid Mine DrainageREDOX in the real world

FeS2 (pyrite) + O2 SO42- + Fe2+

www.state.sd.us/denr/DES/mining/P000106.jpg

http://www.nelpi.org/tarcreek/slides/5s.html

Example

Calculate the equilibrium constant for:2Ag+ (aq) + Hg (l) ↔ 2Ag(s) + Hg2+ (aq)

E° (V)Hg2+ (aq) + 2e- Hg (l) 0.855Ag+ (aq) + e- Ag(s) 0.7994

Primary Batteries (non-rechargeable)Oxyride battery

E° = 1.7 V Cathode: NiOOH + H2O + e- Ni(OH)2 + OH- (1)

Anode: MnO2 (aq) + H2O + e- MnO(OH) (s) + OH-

New battery Vacuum pouring technology Should last 2X longer than alkaline battery

Primary Batteries (non-rechargeable)Oxyride battery

Not responsible for this one

E° = 1.7 V Cathode: NiOOH, MnO2

Anode: Zinc

New battery Vacuum pouring technology Should last 2X longer than alkaline battery