Electrochemistry
Lesson 8
Electrochemical
Cells
Electrochemical cells are Batteries
Alkaline Batteries
KOH
Car Batteries
Pb-Acid H2SO4
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Cell Phone batteries
Lithium Ion Rechargeable battery
Lithium Coin Cell
Space Ship Batteries
Powered by Radioisotopes
Ni-Metal Hydride
Notes on Electrochemical Cells
An electrochemical cell – a system of electrodes,
electrolytes, and salt bridge that allow oxidation and
reduction reactions to occur and electrons to flow through an
external circuit.
1.
2.
3.
Spontaneous redox reaction
Produces electricity from chemicals
Is commonly called a battery
The salt bridge allows ions to migrate from one half-cell to
the other without allowing the solutions to mix.
Analyzing Electrochemical Cells
The reaction that is higher on the reduction chart is the
reduction and the lower is oxidation and is written in
reverse.
For any cell
Oxidation always occurs at the anode and reduction at the
cathode
Electrons flow through the wire and go from anode to
cathode
Anions (- ions) migrate to the anode and cations (+ions)
migrate towards the cathode usually through the salt bridge
1.
Draw and completely analyze a Cu/Sn electrochemical cell.
voltmeter
e-
e-
Higher
0.48 v
Greatest Electron Affinity
Lower
Reduction
Oxidation
Cathode
Na-+
NO3-
Sn
Cu
Anode
Sn(s) → Sn2+ + 2e-
Cu2+ + 2e- → Cu(s)
0.34 v
Cu2+
Sn2+
+0.14 v
Gains mass
NO3-
NO3-
Loses mass
-
+
Overall Reaction:
Cu2+ + Sn → Sn2+ + Cu(s)
0.48 v
The Hydrogen half cell involves a gas and requires an inert or nonreactive Pt
electrode.
Wire to circuit
H2(g) in
H+
ClPt(s)
1 M HCl
Draw a H2/Ag electrochemical cell with a KNO3 salt bridge.
2e-
voltmeter
2e-
0.80 v
1.0 M KNO3
oxidation
Anode
-
Ag
H2
NO3-
H2 → 2H+ + 2ePt
0.00 v
pH decreases
2Ag+ +
H2 →
2Ag
K+
H+
Ag+
Cl-
NO3-
1 M HCl
1 M AgNO3
+ 2H+
Higher
Greater electron affinity
Reduction
Cathode
+
Ag+ + 1e- → Ag(s)
+0.80 v
Gains mass
0.80 v