1. Chemistry 21.1

2. Electrochemical Cells
21.1
Fireflies, anglerfish, luminous shrimp, squid, jellyfish, and even bacteria give off energy in the form of light as a result of redox reactions. You will discover that the transfer of electrons in a redox reaction produces energy.

3. Electrochemical Processes
21.1
Electrochemical Processes
Electrochemical Processes
For any two metals in an activity series, which metal is more readily oxidized?
What type of chemical reaction is involved in all electrochemical processes?

4. Electrochemical Processes
21.1
Electrochemical Processes
For any two metals in an activity series, the more active metal is the more readily oxidized.

5. Electrochemical Processes
21.1
Electrochemical Processes
A Spontaneous Redox Reaction

6. Electrochemical Processes
21.1
Electrochemical Processes
Zinc metal oxidizes spontaneously in a copper-ion solution. a) A zinc strip is immersed in a solution of copper sulfate. b) As the redox reaction proceeds, copper plates out onto the zinc, and the blue copper sulfate solution is replaced by a solution of zinc sulfate. Classifying How can you classify this reaction?

7. Electrochemical Processes
21.1
Electrochemical Processes

8. Electrochemical Processes
21.1
Electrochemical Processes
Redox Reactions and Electrochemistry
All electrochemical processes involve redox reactions.
An electrochemical process is any conversion between chemical energy and electrical energy.
An electrochemical cell is any device that converts chemical energy into electrical energy or electrical energy into chemical energy.

9. Voltaic Cells How does a voltaic cell produce electrical energy? 21.1

10. 21.1
Voltaic Cells
Electrical energy is produced in a voltaic cell by spontaneous redox reactions within the cell.
Voltaic cells (named after their inventor) are electrochemical cells used to convert chemical energy into electrical energy.

11. Constructing a Voltaic Cell
21.1
Voltaic Cells
Constructing a Voltaic Cell
A half-cell is one part of a voltaic cell in which either oxidation or reduction occurs.
The half-cells are connected by a salt bridge—a tube containing a strong electrolyte, often potassium sulfate (K2SO4).

12. The electrode at which oxidation occurs is called the anode.
21.1
Voltaic Cells
An electrode is a conductor in a circuit that carries electrons to or from a substance other than a metal.
The electrode at which oxidation occurs is called the anode.
The electrode at which reduction occurs is called the cathode.

13. 21.1
Voltaic Cells
Volta built his electrochemical cell using piles of silver and zinc plates separated by cardboard soaked in salt water. He used his cell to obtain an electrical current.
Volta built his electrochemical cell using piles of silver and zinc plates separated by cardboard soaked in salt water. He used his cell to obtain an electrical current.

14. How a Voltaic Cell Works
21.1
Voltaic Cells
How a Voltaic Cell Works

15. 21.1 > Electrochemical Cells Voltaic Cells
In this voltaic cell, the electrons generated from the oxidation of Zn to Zn2+ flow through the external circuit (the wire) into the copper strip. These electrons reduce the surrounding Cu2+ to Cu. To maintain neutrality in the electrolytes, anions flow through the salt bridge

16. 21.1 > Electrochemical Cells Voltaic Cells
In this voltaic cell, the electrons generated from the oxidation of Zn to Zn2+ flow through the external circuit (the wire) into the copper strip. These electrons reduce the surrounding Cu2+ to Cu. To maintain neutrality in the electrolytes, anions flow through the salt bridge.

17. 21.1 > Electrochemical Cells Voltaic Cells
In this voltaic cell, the electrons generated from the oxidation of Zn to Zn2+ flow through the external circuit (the wire) into the copper strip. These electrons reduce the surrounding Cu2+ to Cu. To maintain neutrality in the electrolytes, anions flow through the salt bridge.

18. 21.1 > Electrochemical Cells Voltaic Cells
In this voltaic cell, the electrons generated from the oxidation of Zn to Zn2+ flow through the external circuit (the wire) into the copper strip. These electrons reduce the surrounding Cu2+ to Cu. To maintain neutrality in the electrolytes, anions flow through the salt bridge.

19. 21.1 > Electrochemical Cells Voltaic Cells
In this voltaic cell, the electrons generated from the oxidation of Zn to Zn2+ flow through the external circuit (the wire) into the copper strip. These electrons reduce the surrounding Cu2+ to Cu. To maintain neutrality in the electrolytes, anions flow through the salt bridge.

20. Representing Electrochemical Cells
21.1
Voltaic Cells
Representing Electrochemical Cells
You can represent the zinc-copper voltaic cell using the following shorthand.

21. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Using Voltaic Cells as Energy Sources
What current technologies use electrochemical processes to produce electrical energy?

22. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Current technologies that use electrochemical processes to produce electrical energy include dry cells, lead storage batteries, and fuel cells.

23. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Dry Cells
A dry cell is a voltaic cell in which the electrolyte is a paste. The half reactions for one type of dry cell are shown below.

24. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Both dry cells and alkaline batteries are single electrochemical cells that produce about 1.5 V.
Both dry cells and alkaline batteries are single electrochemical cells that produce about 1.5 V. a) The dry cell is inexpensive, has a short shelf life, and suffers from voltage drop when in use. b) The alkaline battery costs more than the dry cell, has a longer shelf life, and does not suffer from voltage drop. Inferring What is oxidized in these cells and what is reduced?

25. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Lead Storage Batteries
A battery is a group of cells connected together. The half-reactions for a lead storage battery are as follows.
One cell of a 12-V lead storage battery is illustrated here. Current is produced when lead at the anode and lead(IV) oxide at the cathode are both converted to lead sulfate. These processes decrease the sulfuric acid concentration in the battery. Reversing the reaction recharges the battery.

26. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
A 12-V car battery consists of six voltaic cells connected together. One cell of a 12-V lead storage battery is illustrated here.
One cell of a 12-V lead storage battery is illustrated here. Current is produced when lead at the anode and lead(IV) oxide at the cathode are both converted to lead sulfate. These processes decrease the sulfuric acid concentration in the battery. Reversing the reaction recharges the battery.

27. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
The lead-acid battery in an automobile acts as a voltaic cell (top) when it supplies current to start the engine. Some of the power from the running engine is used to recharge the battery which then acts as an electrolytic cell (bottom). You will learn more about electrolytic cells in Section 21.3.

28. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
Fuel Cells
Fuel cells are voltaic cells in which a fuel substance undergoes oxidation and from which electrical energy is continuously obtained.

29. Using Voltaic Cells as Energy Sources
21.1
Using Voltaic Cells as Energy Sources
The hydrogen-oxygen fuel cell is a clean source of power. Such cells are often used in spacecraft.
The hydrogen–oxygen fuel cell is a clean source of power. Such cells are often used in spacecraft. Predicting What waste products, if any, are produced?

30. 21.1 Section Quiz.
21.1.

31. 21.1 Section Quiz.
1. Zn is above Pb in the activity series of metals. Which of the following statements is correct?
Zn will react with Pb2+.
Pb2+ will react with Zn2+.
Zn2+ will react with Pb.
Pb will react with Zn2+.

32. 21.1 Section Quiz.
2. The reactions that take place in electrochemical cells involve electron transfers. What name is given to such reactions?
oxidation reactions
reduction reactions
spontaneous redox reactions
double replacement reactions

33. 21.1 Section Quiz.
3. Portable sources of electrical energy consisting of groups of voltaic cells connected together are called
batteries
alkaline cells.
dry cells.
fuel cells.

34. 21.1 Section Quiz.
4. In an automobile storage battery, sulfuric acid (H2SO4) is used as the
cathode.
electrolyte.
anode.
oxidizing agent.

35. 21.1 Section Quiz.
5. In the hydrogen-oxygen fuel cell, the product(s) of the overall reaction is/are
water and hydroxide ions.
hydrogen and oxygen.
water.
hydroxide ions.

36. END OF SHOW