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51 Cards in this Set
- Front
- Back
oxidation
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loss of electrons
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reduction
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gain of electrons
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oxidizing agent
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one that becomes reduced
ex) halogens |
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reducing agent
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one that becomes oxidized
ex) group I/II metals and transition metals |
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oxidation numbers can be known from the periodic table and memorization
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know
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balance MnO4- + I- --> I2 + Mn^2+ (pt 1)
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1. separate into I- --> I2
and MnO4- --> Mn^2+ 2. add water to Mn2+ side and add H+ to MnO4- side to be equivalent 3. balance I- --> I2 4. add electrons to respective sides to get = charges 5. multiply charges to get common number and add up the two separate EQs as one |
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final answer to above?
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10I- + 16H+ +2Mno4- --> 5I2 + 2Mn^2+ + 8H2O
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electrochemical cells (3)
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galvanic
electrolytic concentration |
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which are spontaneous? which are not?
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spontaneous = concentration/galvanic
nonspontaneous = eletrolytic |
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anode = site of oxidation/reduction
cathode = site of oxidation/reduction |
anode = oxidation
cathode = reduction |
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movement of electrons is...
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anode to cathode
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movement of current is...
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cathode to anode
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galvanic cells
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spontaneous = -/\G
EMF = positive produces energy = batteries |
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EMF always/never has the opposite sign of the gibbs free energy
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always
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draw the set up for a galvanic cell
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-2 separate beakers
-salt bridge connecting the two -electrode wire between the two -anode = Zn + Zn/SO4^2- -cathode = Cu + Cu/SO4^2- -anode = predominantly Zn2+ -cathode = predominantly SO4^2- -salt bridge will push Cl- into anode to counter Zn2+ -salt bridge will push K+ into cathode to counter SO4^2- |
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salt bridges are usually made up of inert electrolytes such as
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KCl
NH4NO3 NaSO3 KNO3 KI |
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if the two parts of a galvanic cell were not separated, the Cu2+ ions would react with the Zn bar and no work would be obtained
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know
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galvanic cells require both a wire and a salt bridge to reach EQ
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know
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electrolytic cells
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non-spontaneous = +/\G
-EMF value require energy (require outside source) ex) electrolysis = decompostion |
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draw electrolytic cell
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has battery
+ end is anode side - end is the cathode side -not separated; one container -no salt bridge -NaCl in mix; Cl- attracted to anode and Na+ attracted to cathode |
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electrolytic cells are not separated since it is ______
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non-spontaneous
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the amount of chemical change induced in an electrolytic cell is directly proportional to the number of moles of electrons that are exchanged during a redox rxn
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M^n+ + ne- -->M(s)
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farraday's constant
1F = |
100,000 Coulombs
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concentration cells
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spontaneous = -/\G
+EMF identical electrodes -concentration difference pushes rxn forward |
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concentration cells deal with movement of electrons that results in EQ
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know
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concentration cells; current ceases when concentrations are =
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voltage/EMF = 0 at EQ
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galvanic cells and determing electrode charges
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since the anode = source of e', it is the negative electrode
the cathode = source of protons, it is the positive electrode |
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movement of electrons in a galvanic cell =
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negative to positive
-low electric potential to high electric potential |
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electrolytic cell and electrode charge determination
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the anode is the positive electrode since attached to the positive side of the battery
-the cathode is the negative electrode since attached to the negative side of the battery |
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cathode attracts anions/cations
anode attracts anions/cations |
cations
anions |
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reduction potentials
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measured in Volts
-tendency of a species to acquire electrons and become reduced |
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standard reduction potential (Eo)red
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298K and 1M concentration, 1atm
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a higher (Eo)red means a greater/lesser tendency for reduction to occur
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greater
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a lower (Eo)red means a greater/lesser tendency for reduction to occur
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lesser
-greater chance to oxidize |
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galvanic species and reduction potential; cathode/anode
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higher reduction potential = cathode
lower reduction potential = anode |
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electrolytic cell and reduction potential cathode/anode
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anode = higher reduction potential
cathode = lower reduction potential REVERSED!!! |
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ex)
Ag+ + e- --> Ag(s) Eo = +.8V Tl+ + e- --> Tl(s) Eo = -.34V which is oxidized and reduced? |
both are in reduced format, the larger (+) value is the reduced one...
the other one is oxidized |
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EMF =
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cathode - anode
or reduction + oxidation |
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EMF example
Sm3+ + Rh + 6Cl- --> [RhCl6]3- + Sm reduction potentials are -2.41V for Sm3+ +.44V [RhCl6]3- is it electrolytic or galvanic? |
Sm3+ is being reduced = -2.41V
while Rh + 6Cl- is being oxidized... --reverse the .44V --> -.44V and reduction + oxidation = -2.41V + -.44V = -2.85V electrolytic since EMF = - |
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/\G = -nFEcell
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n = moles of electrons exchanged
F = 100,000Coulombs Ecell = EMF of cell |
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/\G is in joules, not kJ
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!!!
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coulombs = Joules/Volt
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!!!
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Work = q/\V
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know
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effect of concentration on EMF
nerst EQ: Ecell = (Eo)cell - (RT/nF)*(lnQ) |
Q = [products]/[reactants]
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concentration does/does not have an effect on the EMF of a cell
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does
-EMF varies with the changing concentrations of the species involved |
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EMF of a cell can be measured using a ____
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voltmeter
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potentiator
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type of voltmeter that draws no current; can measure difference between two electrodes
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EMF and Equilibrium constant
EQ: /\Go = -RTln(Keq) |
R = 8.3J
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combining equations...
nF(Eo)cell = RTln(Keq) |
know this
if Ecell is +, then ln(Keq) is + --this means K > 1 = products favored if Cell is (-) than ln(Keq) is (-) and K < 1 = favors reactants |
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Keq > 1 is _____ in forward rxn while a Keq < 1 is not
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spontaneous
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if the Keq = 1....then EMF =
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zero
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