2. Redox in Electrochemistry
Electrochemistry is the study of the redox processes by which chemical energy is converted to electrical energy and vice versa.
Section 20-1

3. Redox in Electrochemistry (cont.)
A salt bridge is a pathway to allow the passage of ions from one side to another, so that ions do not build up around the electrodes.
An electrochemical cell is an apparatus that uses a redox reaction to produce electrical energy or uses electrical energy to cause a chemical reaction.
Section 20-1

4. Redox in Electrochemistry (cont.)
A voltaic cell is a type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction.
Section 20-1

5. Chemistry of Voltaic Cells
An electrochemical cell consists of two parts called half-cells, in which the separate oxidation and reduction reactions take place.
The electrode where oxidation takes place is called the anode.
The cathode is the electrode where reduction occurs.
Section 20-1

6. Calculating Electrochemical Cell Potentials
The tendency of a substance to gain electrons is its reduction potential.
Section 20-1

7. Calculating Electrochemical Cell Potentials (cont.)
The standard hydrogen electrode consists of a small sheet of platinum immersed in a hydrochloric acid solution that has a hydrogen ion concentration of 1 M. Hydrogen gas (H2), at a pressure of 1 atm, is bubbled in and the temperature is maintained at 25°C.
Section 20-1

8. Calculating Electrochemical Cell Potentials (cont.)
Formula for cell potential
E0cell = E0reduction – E0oxidation
Section 20-1

9. End of Section 20-1

10. Dry Cells
A battery is one or more voltaic cells in a single package that generates electric current.
Section 20-2

11. Dry Cells (cont.)
A dry-cell is an electrochemical cell in which the electrolyte is a moist paste. The paste in a zinc-carbon cell consists of zinc chloride, manganese(IV) oxide, ammonium chloride, and a small amount of water.
Section 20-2

12. Dry Cells (cont.)
Primary batteries produce electric energy by means of redox reaction that are not easily reversed.
Secondary batteries depend on reversible redox reactions and are rechargeable.
Section 20-2

13. Fuel Cells
A fuel cell is a voltaic cell in which the oxidation of a fuel is used to produce electric energy.
Section 20-2

14. Fuel Cells (cont.) How a fuel cell works
Potassium hydroxide is often the electrolyte.
The oxidation half reaction
2H2(g) + 4OH– → 4H2O + 4e–
The reduction half reaction
O2(g) + 2H2O(l) + 4e– → 4OH–(aq)
When combined, the equation is the same as burning hydrogen in oxygen to form water.
Section 20-2

15. Corrosion
Corrosion is the loss of metal resulting from an oxidation-reduction reaction of the metal with substances in the environment.
Section 20-2

16. Galvanization is the process of coating iron with a layer or zinc.
Corrosion (cont.)
Galvanization is the process of coating iron with a layer or zinc.
Section 20-2

17. End of Section 20-2

18. Reversing Redox Reactions
The use of electrical energy to bring about a chemical reaction is called electrolysis.
An electrochemical cell in which electrolysis occurs is called an electrolytic cell.
Section 20-3

19. Applications of Electrolysis (cont.)
Objects can be electroplated with a metal such as silver.
The cathode is the object to be electroplated, where reduction occurs.
The anode is a bar of silver, where silver is oxidized and silver ions transferred to the cathode.
Section 20-3