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Chapter 21 – Electrochemistry

Chapter 21 – Electrochemistry. 21.1Electrochemical Cells . Electrochemical Cells. Two types of Electrochemical cell Voltaic Cell – An electrochemical cell in which a spontaneous chemical reaction produces a flow of electrons

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Chapter 21 – Electrochemistry

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  1. Chapter 21 – Electrochemistry 21.1Electrochemical Cells

  2. Electrochemical Cells • Two types of Electrochemical cell • Voltaic Cell – An electrochemical cell in which a spontaneous chemical reaction produces a flow of electrons • Electrolytic cell – This electrochemical cell requires an electric current to force a reaction to occur.

  3. Constructing a Voltaic Cell Anode: where oxidation occurs Cathode: where reduction occurs • Salt bridge: tube containing electrolyte which allows current to flow. Ex.Na2SO4(aq) Half-cell: where either oxidation or reduction occurs Anode half reaction Cathode half reaction

  4. How a Voltaic Cell Works Cathode half reaction Anode half reaction Add the two half cells making sure mass and charge are conserved In this Voltaic cell The zinc electrode slowly dissolves as it forms zinc ions. The copper electrode gets larger as copper ions are reduced to copper metal. ANode forOXidation REDuction at CAThode RED CAT : : AN OX

  5. Cell demo

  6. Cell animation

  7. Cell: Kent Chemistry

  8. Reduction Potentials • A voltmeter in the circuit can measure the electrical potential of the cell in Volts. • A table showing the reduction potentials for reduction pairs can be constructed using a hydrogen electrode as a standard (0.00V) • The higher up in the table the pair are, the less likely is the half reaction. • It is the same list as the activity series (table J: Activity series given in the Regents Chem Reference tables.

  9. Reduction Potentials Ex. Write out half cell equations, identify the anode and cathode and identify the direction of electron flow for the following reaction +2 +2 0 Higher one in table J is oxidized Lower one is reduced 0 Zn(s) + Pb2+(aq)  Zn2+(aq) + Pb(s) Step 1: Assign oxidation numbers. LEO GER Step 2: Write out half reactions. Zn(s)  Zn2+(aq) + 2e- OXidation ANode Pb2+(aq)  2e-+ Pb(s) REDuction CAThode Step 3:Use RED CAT and AN OX to decide which reaction occurs at the anode and cathode Step 4: Decide on direction of electron flow. It always flows from the cathode to the anode.

  10. Electron flow Salt bridge - Zn Anode Pb Cathode + Zn2+(aq) Pb2+(aq) Zn(s)  Zn2+(aq) + 2e- OXidation ANode Pb2+(aq)  2e-+ Pb(s) REDuction CAThode

  11. END OF SHOW

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