1. Chemistry 21.2

2. Half-Cells and Cell Potentials
21.2
Batteries provide current to power lights and many kinds of electronic devices—such as the personal digital assistant shown here. You will learn how to calculate electrical potential.

3. 21.2
Electrical Potential
Electrical Potential
What causes the electrical potential of an electrochemical cell?

4. 21.2
Electrical Potential
The electrical potential of a cell results from a competition for electrons between two half-cells.
The electrical potential of a voltaic cell is a measure of the cell’s ability to produce an electric current.
The tendency of a given half-reaction to occur as a reduction is called the reduction potential.

5. 21.2
Electrical Potential
The difference between the reduction potentials of the two half-cells is called the cell potential.

6. 21.2
Electrical Potential
A working voltaic cell can be constructed using a lemon and strips of copper and zinc.
A working voltaic cell can be constructed using a lemon and strips of copper and zinc.

7. Standard Cell Potential
21.2
Standard Cell Potential
Standard Cell Potential
What value is assigned to the electrical potential of a standard hydrogen electrode?

8. Standard Cell Potential
21.2
Standard Cell Potential
The standard cell potential (Eo ) is the measured cell potential when the ion concentrations in the half-cells are 1M, any gases are at a pressure of 101 kPa, and the temperature is 25°C.
cell

9. Standard Cell Potential
21.2
Standard Cell Potential
The standard hydrogen electrode is used with other electrodes so the reduction potentials of the other cells can be measured.
The standard hydrogen electrode is arbitrarily assigned a standard reduction potential of 0.00 V at 25°C.

10. Standard Cell Potential
21.2
Standard Cell Potential
The standard reduction potential of the hydrogen electrode has been assigned a value of 0.00 V.

11. Standard Reduction Potentials
21.2
Standard Reduction Potentials
Standard Reduction Potentials
How can you determine the standard reduction potential of a half-cell?

12. Standard Reduction Potentials
21.2
Standard Reduction Potentials
You can determine the standard reduction potential of a half-cell by using a standard hydrogen electrode and the equation for standard cell potential.

13. Standard Reduction Potentials
21.2
Standard Reduction Potentials
Voltaic Cell
This voltaic cell consists of zinc and hydrogen half-cells. Interpreting Diagrams Where does reduction occur, and what is reduced in this cell?

14. Standard Reduction Potentials
21.2
Standard Reduction Potentials

15. Standard Reduction Potentials
21.2
Standard Reduction Potentials

16. Standard Reduction Potentials
Simulation 27
Simulate the operation of voltaic cells.

17. Calculating Standard Cell Potentials
21.2
Calculating Standard Cell Potentials
Calculating Standard Cell Potentials
How can you interpret the cell potential of a redox reaction in terms of the spontaneity of the reaction?

18. Calculating Standard Cell Potentials
21.2
Calculating Standard Cell Potentials
If the cell potential for a given redox reaction is positive, then the reaction is spontaneous as written. If the cell potential is negative, then the reaction is nonspontaneous.

19. Calculating Standard Cell Potentials
21.2
Calculating Standard Cell Potentials
Table 21.2

20. Calculating Standard Cell Potentials
21.2
Calculating Standard Cell Potentials
Table 21.2
(continued)

21. Determining Reaction Spontaneity

22. Determining Reaction Spontaneity

23. Determining Reaction Spontaneity

24. for Conceptual Problem 21.1
Problem Solving 21.9 Solve Problem 9 with the help of an interactive guided tutorial.

25. 21.1

26. 21.1

27. 21.1

28. 21.1

29. for Sample Problem 21.1
Problem Solving Solve Problem 12 with the help of an interactive guided tutorial.

30. 21.2

31. 21.2

32. 21.2

33. 21.2

34. 21.2 Section Quiz.
21.2.

35. 21.2 Section Quiz.
1. The electrical potential of a cell results from the competition for _________ between two half-cells.
electrolytes
electrons
oxygen
protons

36. 21.2 Section Quiz.
2. All half-cell potentials are measured relative to the standard
hydrogen electrode.
platinum electrode.
oxygen electrode.
copper electrode.

37. 21.2 Section Quiz.
3. The standard reduction potential of a half-cell is determined by comparing it to the
standard hydrogen electrode.
oxidation-half cell.
fluorine half-cell.
lithium half-cell.

38. 21.2 Section Quiz
4. Choose the correct words for the spaces. If the cell potential for a given redox reaction is ______, then the reaction is spontaneous as written. If the cell potential is ________, then the reaction is nonspontaneous.
negative, positive
positive, negative
zero, positive
negative, zero

39. END OF SHOW