P1253814639tnvhJ - PowerPoint PPT Presentation

Title: P1253814639tnvhJ


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Fred J. Grieman
Lec. 36 Recycle Aluminum Fuel
Cells
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Julia Brainerd Hall, Charles's sister, who made
many contributions to the discovery of the
electrolytic means of producing aluminum.
Charles M. Hall at the age of twenty-two
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Fuel
Cells Hydrogen fuel cells, convert flows of
hydrogen and oxygen into water and produce
electricity in the process. At the anode,
hydrogen is forced through a catalyst (usually
platinum or nickel powder) where it is ionized
2H2 ? 4H 4e- or H2 2 OH- ? 2H2O
2e-. The electrons then pass through an
external circuit, where their flow can be
harnessed as electricity, on their way to the
cathode. At the cathode, oxygen reacts with the
products from the anode (the protons and
electrons) O2 4H 4e- ? 2H2O or O2
2H2O 4e- ? 4OH- . Along with heat, this is
the only by-product of the hydrogen fuel cell
the reactants are normally fully utilized. Aside
from electricity and heat, which itself can be
captured and used, water is the only product from
a hydrogen fuel cell. Of course, this is
harmless and so the process has huge
environmental advantages over polluting
combustion engines.
Fuel continually added
Other environmental problems (Where does the H2
come from? What if H2 leaks into the
atmosphere?) http//www.pbs.org/newshour/science/
hydrogen/environment.html http//physicsworld.com/
cws/article/news/17694 http//www.epa.gov/fuelcell
/
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• Final Exam Test Topics
  Chemical Thermodynamics
• Let the lectures, handouts,
  and homework be your guide
• I. First Law
• Definitions of system, surroundings, etc. sign
  convention
• Heat (q), Heat Capacity, Calorimetry, qv, qp, H
  ? E PV, State Functions
• Hesss Law standard states, ?Hof, ?Hocomb,
  ?Hor, endo vs. exothermic
• Work (w) , sign convention, Force thru distance,
  PV work
• Energy, Eint, ?E q w, state function, energy
  is conserved
• II. Second Law
• Spontaneous Process, Development of Entropy
  probability, microstates, example of expansion
• of ideal gas, SklnW, ?S?qrev/T, equivalence of
  these two expressions,
• Third Law Absolute S tabulated

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• III. Gibbs Free Keq
• ?G with change in conditions ?Grxn,T
  ?G?r,T RTlnQ ?G?r,T - RT ln Keq or Keq
  e-?Gor,T ,
• Keq ? f(P) ?G f(T), but ?H, ?S ? f(T)
  so use ?G? ?H?-T?S? lnKeq(T) ?H?/RT - ?S?/RT
• 
  or lnKeq(T2)
  - lnKeq(T1) -?H?/R(1/T2 - 1/T1)
• IV. Electrochemistry, Thermodynamics, Keq
• Balancing Redox via ½ reactions
  Concentration Cell
• Galvanic Cell anode (oxidation), cathode
  (reduction), salt bridge or porous plug
  wire/ammeter
• current I (amps) charge Q (coulombs)
  Faraday constant
• ?E cell voltage (measured with
  potentiometer)
• electrolytic cell (driving rxn in reverse
  of spontaneous direction) cell representations
• ?G wother wext welec for rev.
  process Cell to measure ?G -Q?E -nF?E
  (rev.) ?G? -nF?E?