Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 ELECTROCHEMISTRY Chapter 20. 2 TRANSFER REACTIONS Atom/Group transfer HCl + H 2 O ---> Cl - + H 3 O + Electron transfer Cu(s) + 2 Ag + (aq) ---> Cu.

Similar presentations


Presentation on theme: "1 ELECTROCHEMISTRY Chapter 20. 2 TRANSFER REACTIONS Atom/Group transfer HCl + H 2 O ---> Cl - + H 3 O + Electron transfer Cu(s) + 2 Ag + (aq) ---> Cu."— Presentation transcript:

1 1 ELECTROCHEMISTRY Chapter 20

2 2 TRANSFER REACTIONS Atom/Group transfer HCl + H 2 O ---> Cl - + H 3 O + Electron transfer Cu(s) + 2 Ag + (aq) ---> Cu 2+ (aq) + 2 Ag(s)

3 3 Electron Transfer Reactions Electron transfer reactions are oxidation- reduction or redox reactions.Electron transfer reactions are oxidation- reduction or redox reactions. Redox reactions can result in the generation of an electric current or be caused by imposing an electric current.Redox reactions can result in the generation of an electric current or be caused by imposing an electric current. Therefore, this field of chemistry is often called ELECTROCHEMISTRY.Therefore, this field of chemistry is often called ELECTROCHEMISTRY.

4 4 Why Study Electrochemistry? BatteriesBatteries CorrosionCorrosion Industrial production of chemicals such as Cl 2, NaOH, F 2 and AlIndustrial production of chemicals such as Cl 2, NaOH, F 2 and Al Biological redox reactionsBiological redox reactions The heme group

5 5 Review of Terminology for Redox Reactions OXIDATIONloss of electron(s) by a species; increase in oxidation number.OXIDATIONloss of electron(s) by a species; increase in oxidation number. REDUCTIONgain of electron(s); decrease in oxidation number.REDUCTIONgain of electron(s); decrease in oxidation number. OXIDIZING AGENTelectron acceptor; species is reduced.OXIDIZING AGENTelectron acceptor; species is reduced. REDUCING AGENTelectron donor; species is oxidized.REDUCING AGENTelectron donor; species is oxidized. OXIDATIONloss of electron(s) by a species; increase in oxidation number.OXIDATIONloss of electron(s) by a species; increase in oxidation number. REDUCTIONgain of electron(s); decrease in oxidation number.REDUCTIONgain of electron(s); decrease in oxidation number. OXIDIZING AGENTelectron acceptor; species is reduced.OXIDIZING AGENTelectron acceptor; species is reduced. REDUCING AGENTelectron donor; species is oxidized.REDUCING AGENTelectron donor; species is oxidized.

6 6 Review of Cheesy Ways to remember these terms OIL RIGOIL RIG (Oxidation Is Losing, Reduction Is Gaining)(Oxidation Is Losing, Reduction Is Gaining) LEO (the lion) goes GERLEO (the lion) goes GER Losing Electrons Oxidation, Gaining Electrons ReductionLosing Electrons Oxidation, Gaining Electrons Reduction OLE -OLE - Oxidation Losing ElectronsOxidation Losing Electrons OIL RIGOIL RIG (Oxidation Is Losing, Reduction Is Gaining)(Oxidation Is Losing, Reduction Is Gaining) LEO (the lion) goes GERLEO (the lion) goes GER Losing Electrons Oxidation, Gaining Electrons ReductionLosing Electrons Oxidation, Gaining Electrons Reduction OLE -OLE - Oxidation Losing ElectronsOxidation Losing Electrons

7 7 Oxidation Haiku! Lost an electron But now feeling positive Oxidized is cool!

8 8 OXIDATION-REDUCTION REACTIONS Direct Redox Reaction Oxidizing and reducing agents in direct contact. Cu(s) + 2 Ag+(aq) ---> Cu2+(aq) + 2 Ag(s)

9 9 Copper + Silver Ion

10 10 OXIDATION-REDUCTION REACTIONS Indirect Redox Reaction A battery functions by transferring electrons through an external wire from the reducing agent to the oxidizing agent.

11 11 Electrochemical Cells An apparatus that allows a redox reaction to occur by transferring electrons through an external connector.An apparatus that allows a redox reaction to occur by transferring electrons through an external connector. Product favored reaction ---> voltaic or galvanic cell ----> electric currentProduct favored reaction ---> voltaic or galvanic cell ----> electric current Reactant favored reaction ---> electrolytic cell ---> electric current used to cause chemical change.Reactant favored reaction ---> electrolytic cell ---> electric current used to cause chemical change. This is important to distinguish these types due to subtle differences!This is important to distinguish these types due to subtle differences! Batteries are voltaic cells

12 12 Balancing Equations for Redox Reactions Some redox reactions have equations that must be balanced by special techniques. MnO 4 - + 5 Fe 2+ + 8 H + ---> Mn 2+ + 5 Fe 3+ + 4 H 2 O This is all review from Chapter 5, so you dont need any review…. Right?This is all review from Chapter 5, so you dont need any review…. Right? Mn = +7 Fe = +2 Fe = +3 Mn = +2

13 13 Fine, lets look at some examples! Consider the reduction of Ag + ions with copper metal. Cu + Ag + --give--> Cu 2+ + Ag

14 14 Balancing Equations Step 1:Divide the reaction into half- reactions, one for oxidation and the other for reduction. OxCu ---> Cu 2+ Red Ag + ---> Ag Step 2:Balance each for mass. Already done in this case. Step 3:Balance each half-reaction for charge by adding electrons. Ox Cu ---> Cu 2+ + 2e- Red Ag + + e- ---> Ag

15 15 Balancing Equations Step 4:Multiply each half-reaction by a factor so that the reducing agent supplies as many electrons as the oxidizing agent requires. Reducing agent Cu ---> Cu 2+ + 2e- Oxidizing agent 2 Ag + + 2 e- ---> 2 Ag Step 5:Add half-reactions to give the overall equation. Cu + 2 Ag + ---> Cu 2+ + 2Ag The equation is now balanced for both charge and mass.

16 16 Reduction of VO 2 + with Zn

17 17 Balancing Equations Balance the following in acid solution VO 2 + + Zn ---> VO 2+ + Zn 2+ VO 2 + + Zn ---> VO 2+ + Zn 2+ Step 1:Write the half-reactions OxZn ---> Zn 2+ RedVO 2 + ---> VO 2+ Step 2:Balance each half-reaction for mass. OxZn ---> Zn 2+ Red VO 2 + ---> VO 2+ + H 2 O 2 H + + Add H 2 O on O-deficient side and add H + on other side for H-balance.

18 18 Balancing Equations Step 3:Balance half-reactions for charge. OxZn ---> Zn 2+ + 2e- Rede- + 2 H + + VO 2 + ---> VO 2+ + H 2 O Step 4:Multiply by an appropriate factor. OxZn ---> Zn 2+ + 2e- Red 2e- + 4 H + + 2 VO 2 + ---> 2 VO 2+ + 2 H 2 O Step 5:Add balanced half-reactions Zn + 4 H + + 2 VO 2 + ---> Zn 2+ + 2 VO 2+ + 2 H 2 O

19 19 Tips on Balancing Equations Never add O 2, O atoms, or O 2- to balance oxygen.Never add O 2, O atoms, or O 2- to balance oxygen. Never add H 2 or H atoms to balance hydrogen.Never add H 2 or H atoms to balance hydrogen. Be sure to write the correct charges on all the ions.Be sure to write the correct charges on all the ions. Check your work at the end to make sure mass and charge are balanced.Check your work at the end to make sure mass and charge are balanced. PRACTICE!PRACTICE!

20 20 Lets Look at A Demo! The Hydrolysis of Water!!!


Download ppt "1 ELECTROCHEMISTRY Chapter 20. 2 TRANSFER REACTIONS Atom/Group transfer HCl + H 2 O ---> Cl - + H 3 O + Electron transfer Cu(s) + 2 Ag + (aq) ---> Cu."

Similar presentations


Ads by Google