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143 Cards in this Set

  • Front
  • Back
electrochem is the study of relat betw chemical react and ?
electrical energy
oxidation is ______ of an electr
loss
reduction is ________ of a electron
gain
oxidat always occur with a?
reduct
oxidizing agen causes?
another atom in a redox react to undergo oxidat and is itself reduced
OIL RIG
is a way to remember that?
oxidation is loss, Reduction is gain
why do we use oxidation numbers?
to keep track of how many electr are gained or lost in a react
oxidation of free elements is?
0
N2 , N has an oxidat number of?
0
He has an oxidat number of?
0
oxidation number for a monoatomic number is equal to?
the charge of the ion
Na+ has an ox n of?
+1
oxidation number of each group IA element in a compound is?
+1
oxidation of each gr IIA element in a compound is?
+2
oxidation number of group VIIA element in a compound is?
-1 except when combined with an element of higher electroneg
HCl. ox number of Cl is?
-1
HOCl, oxidat numb of Cl is?
+1
NaH, ox n of H is?
-1
CaH2, oxidat number of H?
-1
the ox n of H is _______ in comp with less electr elements than Hydrogen
-1
the more common ox n of H is?
+1
in most compd the oxidat number of O is?
-2
OF2, oxid number of O is?
+2. bec F is more electroneg than O
in peroxides like BaO2, the oxidat number of O is?
-1
sum of the oxidat numbers in all the atoms present in a neutral comp is?
zero
sum of the oxidat number of the atoms pres in a polyatomic ion is equal to?
the charge of the ion
SO42-, the sum of the oxidat numbers must be?
-2
SnCl2 + PbCl4 --> SnCl4 + PbCl2

which react is oxidized?
Sn. it goes from +2 to +4
most common method for balanc redox equat is the?
half react method. also called the ion electron method
half reaction method is?
used to balance the redox react. equat is seperated into 2 half react. oxidat part and the reduct part
Mn04- + I- ---> I2 + Mn2+
what are the 2 half reactions?
I- --> I2
Mn04- ---> Mn2+
what are the steps for balancing an oxidat reduct reaction?
1. seperate the 2 half react
2. balance the atoms in each half react.
3.
when you are balanc the atoms in oxid reduct what atoms do you leave till last?
H and O
oxid reduct
in an acidic solut, add ________ to balance the O atoms and then add _____ to bal the H atoms
H2O,
H+
oxid reduct
in a basic solut add _________ to balance the O's and H's
OH-, and H20
MnO4- ---> Mn2+
balance the half reaction
Mn04- --> Mn2+ + 4H20
Mn04- + 8 H+ --> Mn2+ + 4H20
balane the charges in each half reaction
2I- ---> I2+ 2e-
5 e- + 8 H+ + Mn04- --> Mn2+ + 4 H20
2I- ---> I2+ 2e-
5 e- + 8 H+ + Mn04- --> Mn2+ + 4 H20
after you bal the charges in each half react what do you need to do?
make sure both half react have the same numb of electr so they will cancel.
2I- ---> I2+ 2e-
5 e- + 8 H+ + Mn04- --> Mn2+ + 4 H20
what do you do next?
5(2I- --> I2 + 2e-)
2(5e- + 8H+ + Mn04- --> Mn2+ + 4 H20)
5(2I- --> I2 + 2e-)
2(5e- + 8H+ + Mn04- --> Mn2+ + 4 H20)

what do you do next?
add the half reactions

10 I- --> 5I2 + 10 e-
16 H+ + 2 Mn04- 10 e- --> 2 Mn2+ + 8 H20
10 I- --> 5I2 + 10 e-
16 H+ + 2 Mn04- 10 e- --> 2 Mn2+ + 8 H20

what will you do to get the final equation?
cancel out the electrons and
any H20s, H+s, or OH-s that appear on both sides of the
equation.

10 I- + 16 H+ + 2 Mn04 ---> 5 I2 + 2 Mn2+ + 8 H20
AN OX and a RED CAT
stands for?
anode is oxidation
cathode is where reduction occurs
what are the 2 types of electrchem cells?
1. galvanic c or voltaic c
2. electrolytic cells
spontan react occur in _______ cells?
galvanic or voltaic cells
galvanic cells are also called?
voltaic cells
nonspon react occur in ?
electrolytic cells
galvanic and electro cells have?
electrodes
redox in a galvanic cell has a _______ change in G
NEGATIVE
galvanic cells ________ energy
supply
galvanic cells
oxid and reduct react are put in seperate?
half cells
batteries are galvanic or electrolytic cells?
galvanic
daniell c is an example of?
a galvanic c
daniell c
zinc bar is put in a?
ZnSO4 solution
danielle c
copper bar is put in ?
CuSO4 solution
danielle cell
anode is?
zinc bar where Zn is oxidized
daniell cell
cathode is?
the copper bar. site of reduction of Cu2+ to Cu
daniell c
what happens at the cathode?
Cu2+ is reduced to Cu
daniell cell
what would happen if the 2 half c were not seperated?
the Cu2+ ions would react directly with the zinc bar and no useful electr work would be done
daniell c
why do you need a salt bridge and a wire to connect the half reactions?
bec otherwise an excess negat ch would build up in solut sorrounding the cathode, and exc posit ch in solut sorrounding the anode
daniell c
salt bridge does what?
permits the exch of cations and anions
daniell cell
the salt bridge usually has?
an inert electrolyte like KCl or NH4NO3.
these ions wont react with the electrodes or with the ions in solution
daniell cell
the cations of the salt bridge flow into the ____________ to bal out the charge of __________
CuSO4 solution
SO42- ions left in solution when the Cu2+ ions deposit as copper metal
daniell cell
electrons flow from _______, toward the ____________
anode,
cathode
daniell cell
electrons flow from the zince bar, which is the ________.
anode
daniell cell
what does the flow of electrons do to the cell?
it depletes the salt bridge and uses up the Cu2+
cell diagram
what are the rules for writing it?
1. react and prod are listed from left to right
anode I anode solut II cathode sol I cathode
2. single vertical line repres a phase boundary
3. double vertical line repres the salt bridge or
cell diagram
how are the reactants and products written?
anode I anode solution II cathode sol I cathode
cell diagram
single vertical line is a?
phase boundary
cell diagram
double vertical line is?
presence of a salt bridge or some other barrier
electrolytic c has a ________ G
positive
electrolytic cell is spontan or nonspont?
nonspontaneous
electrolysis
the half reactions are placed?
in the same container
Zn is oxid to Zn2+
what happens at the anode?
electrolytic c
michael faraday theory
the amount of chem change is directly proportional to?
number of moles of electr that are exch during a redox react
electr c
number of moles exch can be determ from?
balanced half reaction
M n+ + ne- --> M (s)
M n+ + ne- --> M (s)
one mole of M will be prod in an electr c if ________ moles of electr are supplied
n
electr cell
How do you calculate the charge of a mole of electrons?
(1.6 X 10-19 C)( 6.022 X 1023 mole-1e-1)= 96487 C/mol e-
electr cell
what is the charge of a mole of electrons?
96,487 C/mol e-
faradays constant is?
1 F=96,487 C or J/V
t or f
1 f=96,487 c
t
reminder from physics
J=?
J=VC
in an electrolytic cell the anode is __________ and the cathode is __________
anode is positive
cathode is negative
in a galvanic cell, the __________ is negative and the cathode is __________
anode is negative,
cathode is positive
in an electrolytic cell
reduction occurs at the _______
and the __________ is posit and the _______ is negat
reduct occurs at cathode
anode is positiv
cath is negative
galvanic cell
_________ occurs at cathode
____ is neg
_____ is positv
galv cell
reduct occurs at cathode
anode is negat
cath is positiv
electrolytic cell
molten NaCl is electrolyzed to form?
Cl2(g) and Na (l)
oxidation
what occurs at the anode?
cathode
Na+ migrates toward the?
it floats at the top and can be removed
where does the liquid sodium end up?
anode. there they are oxid to Cl2
Cl- ions migrate towards the?
anode of an electr cell is considered to be ?
positive
why is the anode of an electrolytic cell considered pos?
its attach to posit pole of battery and attracts anions from the solut
in an electrolyt cell
Is it the anode or the cathode that attracts anions from the solution?
anode
why is the anode of the galvanic cell considered negative?
bec the spont oxidat react that occurs there is the source of the cells negative charge.
oxidation occurs at the _____ in galvanic and electrolytic cells
anode
CAThode atrracts the CATions
so in a daniel cell, in the copper half cell, what moves towards the cathode?
the copper II cations
CAThode attracts the CATions
in a daniel cell, in the __________ half cell, the copper II cations move towards the cathode
copper
CAThode attracts the CATions
in electrophoresis, the ____________ charged Amino acids will migrate toward the cathode
positively charged
CAThode attracts the CATions
electrophoresis
negativ ch AA will move towards the?
anode
electrophoresis
_________ move towar cathode
_________ move toward the anode
positiv ch aa - cathode
negat ch aa- anode
sometimes when electrolysis is done in aq solut, __________ and not the solute might be oxid or reduc
water
in aq NaCl. if it is electrolyzed, H2O migth be reduced at the cathode to prod?
H2 gas and OH- ions
aq NaCl water be reduced to H2 and OH- instead of?
Na+ being reduced to Na (s)
What can you use to determine the species in a reaction that will be oxidized or reduced?
reduction potential
reduction potential is?
tendency of a species to acquire electrons and be reduced
reduction potential
the more positive the potential the greater?
the species tendency to be reduced
reduct pot
the more ____________, the greater ___________
more posit the potent,
greater tend to be reduced
reduct potential
___________ the reduct potent,
____________ tendency to be reduced
more posit the reduct potent,
greater the tendency to be reduced
reduct potential
what is the mnemonic?
A positive potential means more likely to succeed.
a reduct potent is measured in?
volts (V)
a reduct pot is defined relative to?
a standard hydrogen electrode
(SHE)
SHE is?
standard hydrogen electrode
SHE has a potent of?
0.00 volts
Standard reduction potential Eo is measured under?
standard condit
what are standard conditions?
25 C
1 M conc for each particip ion, part press of 1 ATM for each gas and metals in pure state
higer Eo mean?
greater tendenc for reduct to occur
lower Eo means?
a greater tend for oxidat to occur
a ___________ Eo means a greater tend for reduct to occur
higher
Ag+ + e -> Ag (s) E° = +0.80 V
Tl+ + e- -> Tl(s) E°= -0.34 V
which species will be oxid and which will be reduced?
Ag+ will be red to Ag cause it has the higher Eo
to get the oxidat potential of a given half reaction you have to?
1.the reduct half react has to be reversed.
2. sign of reduct potent has to be reversed
standard electromotive force is?
EMF.
the differ in potential betw the 2 half cells
how do you figure out the EMF?
add the stand reduct pot of the reduc species and the stand oxidat potent of the oxidized species
t or f
when adding stand potent do not multiply by the number of moles oxid or reduc
t
EMF= Eo red + ?
EMF= Eo red + Eo ox
a galvanic cell has a ___________ EMF
positive
an electrolytic cell has a ____________ EMF
negative
standard reduction potentials for Sm3+ and
[RhCI6]3- are -2.41 V and +0.44 V respectively, EMF of reaction:
Sm3- + Rh + 6 Cl- -> [RhCI6]3- + Sm
who is getting reduced?
Sm3+ is getting reduced
standard reduction potentials for Sm3+ and
[RhCI6]3- are -2.41 V and +0.44 V respectively, EMF of reaction:
Sm3- + Rh + 6 Cl- -> [RhCI6]3- + Sm
who is getting oxidized?
Rh is oxidized to Rh3+
standard reduction potentials for Sm3+ and
[RhCI6]3- are -2.41 V and +0.44 V respectively, EMF of reaction:
Sm3- + Rh + 6 Cl- -> [RhCI6]3- + Sm
whats the EMF?
-2.41 V + -.44 V
=-2.85
standard reduction potentials for Sm3+ and
[RhCI6]3- are -2.41 V and +0.44 V respectively, EMF of reaction:
Sm3- + Rh + 6 Cl- -> [RhCI6]3- + Sm
if EMF is - 2.85, what kind of cell is this?
electrolytic
standard reduction potentials for Sm3+ and
[RhCI6]3- are -2.41 V and +0.44 V respectively, EMF of reaction:
Sm3- + Rh + 6 Cl- -> [RhCI6]3- + Sm
if EMF is -2.85. in which direct will the react be spontaneous?
to the left
a positive ch in G or Gibbs free energy is spont or non spont?
it is not spontant
a ch in G that is negat is spont or non spont?
spont
How do you determ the spontaneity of a reaction?
use ch in G
the maximum amount of useful work produced by a chemical reaction is
ch in G
or Gibbs free energy
electrochem cell the work done is dependent on?
number of coulombs and the energy available
electrochem cell
ch in G=
ch G= -nFEcell
-nFEcell=?
ch in G
∆G= -nFEcell
what is F
faraday's constant
∆G= -nFEcell
in terms of units, what do you have to watch out for?
that F and G are both expressed in J. You cant have one in J and the other in KJ
∆Go= -nFEocell
this means that the react?
took place under standard conditions
∆G= -nFEcell
∆G is negative only if?
EMF is positive
∆G is ________, when __________ is positive
negative,
EMF is positive