Cmc chapter 20

2. Chapter Menu Electrochemistry Section 20.1 Voltaic Cells Section 20.2 Batteries Section 20.3 Electrolysis Exit Click a hyperlink or folder tab to view the corresponding slides. 3. Section 20-1 Section 20.1Voltaic Cells

Describea way to obtain electrical energy from a redox reaction.

oxidation:the loss of electrons from the atoms of a substance; increases an atoms oxidation number

Identifythe parts of a voltaic cell, and explain how each part operates.

Calculatecell potentials, and determine the spontaneity of redox reactions.

reduction:the gain of electrons by the atoms of a substance; decreases the atoms oxidation number 4. Section 20-1 Section 20.1Voltaic Cells(cont.) salt bridge electrochemical cell voltaic cell half-cell In voltaic cells, oxidation takes place at the anode, yielding electrons that flow to the cathode, where reduction occurs. anode cathode reduction potential standard hydrogen electrode 5. Section 20-1 Redox in Electrochemistry

Electrochemistry is the study of the redox processes by which chemical energy is converted to electrical energy and vice versa.

Redox reactions involve a transfer of electrons from the species that is oxidized to the species that is reduced.

6. Section 20-1 Redox in Electrochemistry(cont.) 7. Section 20-1 Redox in Electrochemistry(cont.)

Asalt bridgeis a pathway to allow the passage of ions from one side to another, so that ions do not build up around the electrodes.

Anelectrochemical cell is an apparatus that uses a redox reaction to produce electrical energy or uses electrical energy to cause a chemical reaction.

8. Section 20-1 Redox in Electrochemistry(cont.)

Avoltaic cellis a type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction.

9. Section 20-1 Chemistry of Voltaic Cells

An electrochemical cell consists of two parts calledhalf-cells , in which the separate oxidation and reduction reactions take place.

The electrode where oxidation takes place is called theanode .

Thecathodeis the electrode where reduction occurs.

10. Section 20-1 Chemistry of Voltaic Cells(cont.)

Electric potential energy is a measure of the amount of current that can be generated from a voltaic cell to do work.

Electric charge can flow between two points only when a difference in electric potential energy exists between the two points.

A volt is a unit used to measure cell potentialthe force from the difference in electric potential energy between two electrodes.

11. Section 20-1 Calculating Electrochemical Cell Potentials

The tendency of a substance to gain electrons is itsreduction potential .

When two half-reactions are coupled, the voltage generated corresponds to the difference in potential between the half-reactions.

12. Section 20-1 Calculating Electrochemical Cell Potentials(cont.)

Thestandard hydrogen electrodeconsists of a small sheet of platinum immersed in a hydrochloric acidsolution that has ahydrogen ionconcentration of 1M .Hydrogen gas (H 2 ), at apressure of 1 atm, isbubbled in and thetemperature is maintained at 25C.

13. Section 20-1 Calculating Electrochemical Cell Potentials(cont.)

The standard hydrogen electrode is the standard against which all other reduction potentials are measured.

14. Section 20-1 Calculating Electrochemical Cell Potentials(cont.) 15. Section 20-1 Calculating Electrochemical Cell Potentials(cont.)

Formula for cell potential

E 0 cell=E 0 reduction E 0 oxidation

16. Section 20-1 Use Standard Reduction Potentials

Cell potentials can be used to determine if a proposed reaction under standard conditions will be spontaneous.

If the calculated potential is positive, the reaction is spontaneous.

If the calculated potential is negative, the reaction is not spontaneous.

Section 20-1 Section 20.1 Assessment In electrochemistry, the site where oxidation occurs is called ____.A. electrode B. anode C. cathode D. ion 18.

Section 20-1 Section 20.1 Assessment The standard potential of a voltaic cell is the difference between the:A. electrode voltage B. standard reduction potentialof the cell and hydrogen C. standard reduction potentialsof the half-cell reactions D. half-cell reactions and thesalt bridge 19. End of Section 20-1 20. Section 20-2 Section 20.2Batteries

Describethe structure, composition, and operation of the typical carbon-zinc dry-cell battery.

reversible reaction:a reaction that can take place in both the forward and reverse directions

Distinguishbetween primary and secondary batteries, and give two examples of each type.

Explainthe structure and operation of the hydrogen-oxygen fuel cell.

Describethe process of corrosion of iron and methods to prevent corrosion.

21. Section 20-2 Section 20.2Batteries(cont.) battery dry cell primary battery secondary battery Batteries are voltaic cells that use spontaneous reactions to provide energy for a variety of purposes. fuel cell corrosion galvanization 22. Section 20-2 Dry Cells

Abatteryis one or more voltaic cells in a single package that generates electric current.

23. Section 20-2 Dry Cells(cont.)

Adry-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.

The anode is the zinc shell.

The cathode is a carbon rod, but reduction occurs in the paste.

In the alkaline cell, zinc is in a powdered form and mixed with potassium hydroxide contained in a steel case.

Alkaline batteries are small and more useful in small devices.

Silver batteries are similar to alkaline but smaller.

Primary batteriesproduce electric energy by means of redox reaction that are not easily reversed.

Secondary batteries depend on reversible redox reactions and are rechargeable.

27. Section 20-2 Lead-Acid Storage Battery

Lead-acid storage batteries are common in automobiles.

The electrolyte solution is sulfuric acid, hence the name.

The anode consists of grids of porous lead.

The cathode consists of lead grids filled with lead(IV) oxide.

28. Section 20-2 Lithium Batteries

Lithium is the lightest known metal and has the lowest standard reduction potential of the metallic elements.

Lithium batteries can be either primary or secondary.

29. Section 20-2 Fuel Cells

Afuel cellis a voltaic cell in which the oxidation of a fuel is used to produce electric energy.

30. Section 20-2 Fuel Cells(cont.)

How a fuel cell works

Potassium hydroxide is often the electrolyte.

The oxidation half reaction

2H 2 (g) + 4OH -> 4H 2 O + 4e

The reduction half reaction

O 2 (g) + 2H 2 O(l) + 4e -> 4OH (aq)

When combined, the equation is the same as burning hydrogen in oxygen to form water.

31. Section 20-2 Corrosion

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

Rusting begins in a chip or pit in the iron surface, which become the anode.

Fe(s) -> Fe 2+ (aq) + 2e

Iron(II) becomes part of the water solution.

32. Section 20-2 Corrosion(cont.)

The cathode is usually at the edge of the water drop where water, iron, and air come into contact.

The reduction reaction is O 2 (g) + 4H + (aq)+ 4e -> 2H 2 O(l).

Next the oxidation 4Fe 2+ (aq) + 2O 2 (g) + 2H 2 O(l) + 4e -> 2Fe 2 O 3 (s) + 4H + .

Rusting is slow, but salts speed the process.

33. Section 20-2 Corrosion(cont.) 34. Section 20-2 Corrosion(cont.)

Paint and other covers seal out moisture to prevent corrosion.

Blocks of metal that are more easily oxidized than steel, such as magnesium, aluminum, or titanium, are often attached to the hulls of shipsthey corrode while the iron in the hull is protected.

35. Section 20-2 Corrosion(cont.)

Galvanizationis the process of coating iron with a layer or zinc.

Zinc oxidizes at the surface, creating a layer of metal-oxide that protects from further corrosion.

Section 20-2 Section 20.2 Assessment Which type of battery has a reversible spontaneous reaction? A. alkaline battery B. secondary battery C. primary battery D. zinc-carbon battery 37.

Section 20-2 Section 20.2 Assessment Which is NOT a method of preventing corrosion?A. painting B. galvanization C. coating with electrolytes D. sacrificial anode 38. End of Section 20-2 39. Section 20-3 Section 20.3Electrolysis

Describehow it is possible to reverse a spontaneous redox reaction in an electrochemical cell.

redox reaction:an oxidation-reduction reaction electrolysis electrolytic cell

Comparethe reactions involved in the electrolysis of molten sodium chloride with those in the electrolysis of brine.

Discussthe importance of electrolysis in the smelting and purification of metals.

In electrolysis, a power source causes nonspontaneous reactions to occur in electrochemical cells. 40. Section 20-3 Reversing Redox Reactions

The use of electrical energy to bring about a chemical reaction is calledelectrolysis .

An electrochemical cell in which electrolysis occurs is called anelectrolytic cell .

41. Section 20-3 Applications of Electrolysis

Electrolysis of water is one method of obtaining hydrogen gas for commercial use.

42. Section 20-3 Applications of Electrolysis(cont.)

Electrolysis can separate molten sodium chloride into sodium metal and chlorine gas in a chamber called a Downs cell.

In the decomposition of brine, an aqueous solution of NaCl, electrolysis is used to produce hydrogen gas, chlorine gas, and sodium hydroxide.

The Hall-Hroult process requires large amounts of energy, which is the primary reason for recycling aluminum.

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 Section 20.3 Assessment Which of the following is NOT a product of electrolysis of brine?A. Chlorine gas B. Hydrogen gas C. Sodium hydroxide solution D. Sodium metal 47.

Section 20-3 Section 20.3 Assessment What is required to drive a nonspontaneous reaction in an electrolytic cell?A. electrodes B. additional ions C. an energy source D. an electrolyte 48. End of Section 20-3 49. Resources Menu Chemistry Online Study Guide Chapter Assessment Standardized Test Practice Image Bank Concepts in Motion 50. Study Guide 1 Section 20.1Voltaic Cells Key Concepts

In a voltaic cell, oxidation and reduction take place at electrodes separated from each other.

The standard potential of a half-cell reaction is its voltage when paired with a standard hydrogen electrode under standard conditions.

The reduction potential of a half-cell is negative if it undergoes oxidation when connected to a standard hydrogen electrode. The reduction potential of a half-cell is positive if it undergoes reduction when connected to a standard hydrogen electrode.

51. Study Guide 1 Section 20.1Voltaic Cells(cont.) Key Concepts

The standard potential of a voltaic cell is the difference between the standard reduction potentials of the half-cell reactions.

52. Study Guide 2 Section 20.2Batteries Key Concepts

Primary batteries can be used only once; secondary batteries can be recharged.

When a battery is recharged, electric energy supplied to the battery reverses the direction of the batterys spontaneous reaction.

Fuel cells are batteries in which the substance oxidized is a fuel from an external source.

Methods of preventing corrosion are painting, coating with another metal, or using a sacrificial anode.

53. Study Guide 3 Section 20.3Electrolysis Key Concepts

In an electrolytic cell, an outside source of power causes a nonspontaneous redox reaction to occur.

The electrolysis of molten sodium chloride yields sodium metal and chlorine gas. The electrolysis of brine yields hydrogen gas, sodium hydroxide, and chlorine gas.

Metals such as copper are purified in an electrolytic cell.

Electrolysis is used to electroplate objects and to produce pure aluminum from its ore.

Chapter Assessment 1 A salt bridge is used for what? A. electrolysis B. allowing ions to move fromone half-cell to the other C. increasing the reductionpotential D. linking multiple voltaic cellstogether 55.

Chapter Assessment 2 Batteries that can be used more than once are also called ____. A. primary batteries B. secondary batteries C. tertiary batteries D. fuel cells 56.

Chapter Assessment 3 Corrosion is loss of metal by what mechanism? A. electrolysis B. galvanization C. oxidation-reduction reaction D. salt bridge 57.

Chapter Assessment 4 Electrolysis of H 2 O results in what products? A. H +and OH B. H 2 O 2and O 2 C. NaOH and H 2 D. H 2and O 2 58.

Chapter Assessment 5 Which of the following is NOT a dry-cell?A. a car battery B. a silver battery C. a zinc-carbon battery D. an alkaline battery 59.

STP 1 Which is NOT a characteristic of an acid? A. sour taste B. conduct electricity in solution C. reactivity with some metals D. slippery feel 60.

STP 2 Which metal has the lowest standard reduction potential? A. Sodium B. Magnesium C. Lithium D. Silver 61.

STP 3 Which statement is NOT true about batteries? A. Batteries are composed of twohalf-cells. B. Secondary batteries are alsoknown as storage batteries. C. Redox reactions in zinc-carbonbatteries are easily reversible. D. Batteries are compact forms ofvoltaic cells. 62.

STP 4 Which of the following is the equation used to calculate a cell potential? A. E 0 cell=E 0 oxidation E 0 reduction B. E 0 cell=E 0 reduction E 0 oxidation C. E 0 cell=E 0 reduction+ E 0 oxidation D. E 0 cell=E 0 reduction xE 0 oxidation 63.

STP 5 Which is NOT an example of a sacrificial anode?A. magnesium B. aluminum C. iron D. titanium 64. IB Menu Click on an image to enlarge. 65. IB 1 66. IB 2 67. IB 3 68. IB 4 69. IB 5 70. IB 6 71. IB 7 72. IB 8 73. IB 9 74. IB 10 75. IB 11 76. IB 12 77. IB 13 78. IB 14 79. IB 15 80. IB 16 81. IB 17 82. IB 18 83. IB 19 84. CIM Figure 20.2Voltaic Cells 85. Help Click any of the background top tabs to display the respective folder. Within the Chapter Outline, clicking a section tab on the right side of the screen will bring you to the first slide in each respective section. Simple navigation buttons will allow you to progress to the next slide or the previous slide. The Return button will allow you to return to the slide that you were viewing when you clicked either the Resources or Help tab. The Chapter Resources Menu will allow you to access chapter specific resources from the Chapter Menu or any Chapter Outline slide. From within any feature, click the Resources tab to return to this slide. To exit the presentation, click the Exit button on the Chapter Menu slide or hit Escape [Esc] on your keyboards while viewing any Chapter Outline slide. 86. End of Custom Shows This slide is intentionally blank.

Cmc chapter 20

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