1 ELECTROCHEMISTRYELECTROCHEMISTRY Redox reactions results in the generation of an electric current (electricity).Redox reactions results in the generation of an electric current (electricity). Therefore, this field of chemistry is often called ELECTROCHEMISTRY.Therefore, this field of chemistry is often called ELECTROCHEMISTRY.

2 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

3 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. Batteries are voltaic cells

4 Electron transfer Electron transfer With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.” Zn is oxidized and is the reducing agent Zn(s) ---> Zn 2+ (aq) + 2e-Zn is oxidized and is the reducing agent Zn(s) ---> Zn 2+ (aq) + 2e- Cu 2+ is reduced and is the oxidizing agent Cu 2+ (aq) + 2e- ---> Cu(s)Cu 2+ is reduced and is the oxidizing agent Cu 2+ (aq) + 2e- ---> Cu(s) The electrons are transferred directly when the reactants collide. No useful work is obtained from the chemical energy involved which is instead released as heat!

5 Harnessing the energy We can harness this energy if we separate the oxidizing agent from the reducing agent, thus requiring the e- transfer to occur through a wire! We can harness the energy that way to run a motor, light a bulb, etc.

6 To obtain a useful current, the oxidizing and reducing agents are separated so that electron transfer occurs thru an external wire.To obtain a useful current, the oxidizing and reducing agents are separated so that electron transfer occurs thru an external wire. Galvanic cell This is accomplished in a GALVANIC or VOLTAIC cell. A group of such cells is called a battery.

7 A voltaic cell cannot operate if a charge differential exists.. Sustained electron flow cannot occur in this. Why not? As soon as electrons flow a separation of charge occurs which stops the flow of electrons. How do we fix it? As soon as electrons flow a separation of charge occurs which stops the flow of electrons. How do we fix it?

8 salt bridge—It contains concentrated solutions of inert electrolyte. It’s job is to balance the charge in each half reaction compartments. It connects the two compartments, ions flow from it, AND keeps each “cell” neutral. A salt bridge completes the circuit by allowing the migration of anions from one container into the salt bridge and from the salt bridge into the other container.

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10 Observations There is a flow of electrical current through the external circuit. The zinc rod loses weight, while the copper rod acquires weight. The concentration of ZnSO 4 solution increases, while that of CuSO 4 solution decreases. The two solutions in the beakers have electrical neutrality.

11 Electrons travel thru external wire. Salt bridge allows anions and cations to move between electrode compartments.Salt bridge allows anions and cations to move between electrode compartments. Electrons travel thru external wire. Salt bridge allows anions and cations to move between electrode compartments.Salt bridge allows anions and cations to move between electrode compartments. Zn --> Zn e- Cu e- --> Cu <--AnionsCations--> Oxidation Anode Negative Oxidation Anode Negative Reduction Cathode Positive Reduction Cathode Positive RED CAT