Utilizes relationship between chemical potential energy

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• Utilizes relationship between chemical potential
  energy electrical energy

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Redox Reactions

• battery to start car
• prevent corrosion
• cleaning with bleach (oxidizing agent)
• Na, Al, Cl prepared or purified by redox
  reactions
• breathing
• O2 ? H2O and CO2

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Redox Reactions

• Synthesis
• Decomposition
• Single Replacement
• DR rxns NOT redox rxn!

Redox rxns
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Predicting Redox Reactions

• Table J predict if given redox reaction will
  occur
• metals donate electrons to ion of metals below
  itself
• nonmetal steals electrons from ion of nonmetal
  below itself

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Predicting Single Replacement Redox Reactions

• Element Compound ?
• New Element New Compound
• If element above swapable ion, reaction is
  spontaneous
• If element below swapable ion, reaction is not
  spontaneous

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Predicting Redox Reactions

• A BX ? B AX
• If metal A above metal B (Table J) reaction is
  spontaneous
• X AY ? Y AX
• If nonmetal X above nonmetal Y (Table J)
  reaction is spontaneous

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Spontaneous or not?

• Li AlCl3 ?
• Cs CuCl2 ?
• I2 NaCl ?
• Cl2 KBr ?
• Fe CaBr2 ?
• Mg Sr(NO3)2 ?
• F2 MgCl2 ?

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Started with 1. Zn(NO3)2 Cu 2. AgNO3
Cu Which beaker had Zn ions which had Ag ions?
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Overview of Electrochemistry

• TWO kinds of cells
• 1. Galvanic or Voltaic (NYS Electrochemical)
• Use spontaneous rxn to produce flow of electrons
  (electricity) Exothermic
• 2. Electrolytic
• Use flow of electrons (electricity) to force
  nonspontaneous rxn to occur Endothermic

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Vocabulary

• Redox
• Half-reaction
• Oxidation
• Reduction
• Cell
• Half-Cell
• Electrode

• Anode
• Cathode
• Galvanic
• Voltaic
• Electrochemical
• Electrolytic
• Salt bridge

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Electrochemical Cells

• spontaneous SR redox rxn produces flow of
  electrons
• Electrons flow from oxidized substance to reduced
  substance
• Names Galvanic cells, voltaic cells, or
  electrochemical cells (NYS)

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Electrochemical Cells

• Redox rxn arranged so electrons forced to flow
  through wire
• When electrons travel through a wire, can make
  them do work - light a bulb,ring a buzzer
• oxidation reduction reactions must be separated
  physically

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Half-Cell

• Place where each half-reaction takes place
• ½ cells
• 2 needed for complete redox rxn
• connected by wire so electrons flow through
• connected by salt bridge to maintain electrical
  neutrality

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Schematic of Galvanic/Voltaic Cell
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Parts of a Galvanic/Voltaic Cell

• 2 half-cells
• One for oxidation rxn
• One for reduction rxn
• Each consists of
• container with aqueous solution electrode
  (surface where electron transfer takes place)
• Wire connects electrodes
• Salt bridge connects solutions

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How much work can you get out of this reaction?

• can measure voltage by allowing electrons to
  travel through voltmeter
• galvanic cell is a battery
• not easy battery to transport or use in real-life
  applications

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Electrode
Surface at which oxidation or reduction
half-reaction occurs Anode Cathode
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An Ox Ate a Red Cat

• Anode Oxidation
• the anode location for the oxidation
  half-reaction
• Reduction Cathode
• the cathode location for the reduction
  half-reaction

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Anode / Cathode

• How know which electrode is which?
• Table J predict which electrode anode and which
  electrode is cathode

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Anode

• Anode Oxidation Electron Donor
• anode is metal higher on Table J

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Cathode

• Cathode Reduction Electron Acceptor
• cathode is metal lower on Table J

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Zn is above Cu, Zn is anode
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Direction of Electron Flow(through wire)

• Anode ? Cathode

Anode ? Cathode
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Positive Negative Electrode

• Negative electrode (anode)
• where electrons originate
• here its Zn electrode
• Positive electrode (cathode)
• electrode that attracts electrons
• here its the Cu electrode

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Aqueous Solution

• Solution containing ions of same element as
  electrode
• Cu electrode
• Solution Cu(NO3)3 or CuSO4
• Zn electrode
• Solution Zn(NO3)2 or ZnSO4

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Salt Bridge

• migration of ions between half-cells
• necessary to maintain electrical neutrality
• reaction can not proceed without salt bridge

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A(s) BX(aq) ? B(s) AX(aq)

• SR rxn occurs during operation of
  galvanic/voltaic cell
• One electrode gains mass (B) and one electrode
  dissolves (A)
• concen of metal ions ? in one soln (making AX)
  ? in other soln (using up BX)

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Half-Reactions

• Zn ? Zn2 2e-
• Cu2 2e- ? Cu

Which electrode is dissolving? Which species is
increasing its mass?
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Zn Cu2 ? Zn2 Cu

• Which electrode is gaining mass?
• Which species is getting more dilute?

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When the reaction reaches equilibrium

• voltage is 0!
• electrons no longer flow

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Construct Galvanic Cell with Al Pb

• Use Table J to identify anode cathode
• Draw Cell
• put in electrodes solutions
• Label
• anode, cathode, direction of electron flow in
  wire, direction of positive ion flow in salt
  bridge, positive electrode, negative electrode
• Negative electrode where electrons originate
  Positive electrode attracts electrons

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What are half-reactions?

• Al ? Al3 3e-
• Pb2 2e- ? Pb

• Pb2 ions are in the solution
• Ions pick up 2 electrons plate together on
  surface of Pb electrode as Pb0

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Overall Rxn

• 2(Al ? Al3 3e-)
• 3(Pb2 2e- ? Pb)

2Al 3Pb2 6e-? 2Al3 3Pb 6e-
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2Al 3Pb2 ? 2Al3 3Pb

• Which electrode is losing mass?
• Which electrode is gaining mass?
• Whats happening to the Al3?
• Whats happening to the Pb2?

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Application Batteries
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Dry Cell
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Mercury battery
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Application Corrosion
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Corrosion Prevention
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Whats wrong with this picture?