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143 Cards in this Set
- Front
- Back
electrochem is the study of relat betw chemical react and ?
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electrical energy
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oxidation is ______ of an electr
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loss
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reduction is ________ of a electron
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gain
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oxidat always occur with a?
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reduct
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oxidizing agen causes?
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another atom in a redox react to undergo oxidat and is itself reduced
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OIL RIG
is a way to remember that? |
oxidation is loss, Reduction is gain
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why do we use oxidation numbers?
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to keep track of how many electr are gained or lost in a react
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oxidation of free elements is?
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0
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N2 , N has an oxidat number of?
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0
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He has an oxidat number of?
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0
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oxidation number for a monoatomic number is equal to?
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the charge of the ion
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Na+ has an ox n of?
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+1
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oxidation number of each group IA element in a compound is?
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+1
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oxidation of each gr IIA element in a compound is?
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+2
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oxidation number of group VIIA element in a compound is?
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-1 except when combined with an element of higher electroneg
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HCl. ox number of Cl is?
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-1
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HOCl, oxidat numb of Cl is?
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+1
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NaH, ox n of H is?
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-1
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CaH2, oxidat number of H?
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-1
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the ox n of H is _______ in comp with less electr elements than Hydrogen
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-1
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the more common ox n of H is?
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+1
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in most compd the oxidat number of O is?
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-2
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OF2, oxid number of O is?
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+2. bec F is more electroneg than O
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in peroxides like BaO2, the oxidat number of O is?
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-1
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sum of the oxidat numbers in all the atoms present in a neutral comp is?
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zero
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sum of the oxidat number of the atoms pres in a polyatomic ion is equal to?
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the charge of the ion
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SO42-, the sum of the oxidat numbers must be?
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-2
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SnCl2 + PbCl4 --> SnCl4 + PbCl2
which react is oxidized? |
Sn. it goes from +2 to +4
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most common method for balanc redox equat is the?
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half react method. also called the ion electron method
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half reaction method is?
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used to balance the redox react. equat is seperated into 2 half react. oxidat part and the reduct part
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Mn04- + I- ---> I2 + Mn2+
what are the 2 half reactions? |
I- --> I2
Mn04- ---> Mn2+ |
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what are the steps for balancing an oxidat reduct reaction?
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1. seperate the 2 half react
2. balance the atoms in each half react. 3. |
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when you are balanc the atoms in oxid reduct what atoms do you leave till last?
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H and O
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oxid reduct
in an acidic solut, add ________ to balance the O atoms and then add _____ to bal the H atoms |
H2O,
H+ |
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oxid reduct
in a basic solut add _________ to balance the O's and H's |
OH-, and H20
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MnO4- ---> Mn2+
balance the half reaction |
Mn04- --> Mn2+ + 4H20
Mn04- + 8 H+ --> Mn2+ + 4H20 |
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balane the charges in each half reaction
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2I- ---> I2+ 2e-
5 e- + 8 H+ + Mn04- --> Mn2+ + 4 H20 |
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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.
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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) |
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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 |
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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 |
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AN OX and a RED CAT
stands for? |
anode is oxidation
cathode is where reduction occurs |
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what are the 2 types of electrchem cells?
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1. galvanic c or voltaic c
2. electrolytic cells |
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spontan react occur in _______ cells?
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galvanic or voltaic cells
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galvanic cells are also called?
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voltaic cells
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nonspon react occur in ?
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electrolytic cells
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galvanic and electro cells have?
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electrodes
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redox in a galvanic cell has a _______ change in G
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NEGATIVE
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galvanic cells ________ energy
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supply
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galvanic cells
oxid and reduct react are put in seperate? |
half cells
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batteries are galvanic or electrolytic cells?
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galvanic
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daniell c is an example of?
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a galvanic c
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daniell c
zinc bar is put in a? |
ZnSO4 solution
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danielle c
copper bar is put in ? |
CuSO4 solution
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danielle cell
anode is? |
zinc bar where Zn is oxidized
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daniell cell
cathode is? |
the copper bar. site of reduction of Cu2+ to Cu
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daniell c
what happens at the cathode? |
Cu2+ is reduced to Cu
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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
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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
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daniell c
salt bridge does what? |
permits the exch of cations and anions
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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 |
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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 |
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daniell cell
electrons flow from _______, toward the ____________ |
anode,
cathode |
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daniell cell
electrons flow from the zince bar, which is the ________. |
anode
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daniell cell
what does the flow of electrons do to the cell? |
it depletes the salt bridge and uses up the Cu2+
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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 |
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cell diagram
how are the reactants and products written? |
anode I anode solution II cathode sol I cathode
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cell diagram
single vertical line is a? |
phase boundary
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cell diagram
double vertical line is? |
presence of a salt bridge or some other barrier
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electrolytic c has a ________ G
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positive
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electrolytic cell is spontan or nonspont?
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nonspontaneous
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electrolysis
the half reactions are placed? |
in the same container
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Zn is oxid to Zn2+
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what happens at the anode?
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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
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electr c
number of moles exch can be determ from? |
balanced half reaction
M n+ + ne- --> M (s) |
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M n+ + ne- --> M (s)
one mole of M will be prod in an electr c if ________ moles of electr are supplied |
n
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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-
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electr cell
what is the charge of a mole of electrons? |
96,487 C/mol e-
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faradays constant is?
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1 F=96,487 C or J/V
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t or f
1 f=96,487 c |
t
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reminder from physics
J=? |
J=VC
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in an electrolytic cell the anode is __________ and the cathode is __________
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anode is positive
cathode is negative |
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in a galvanic cell, the __________ is negative and the cathode is __________
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anode is negative,
cathode is positive |
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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 |
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galvanic cell
_________ occurs at cathode ____ is neg _____ is positv |
galv cell
reduct occurs at cathode anode is negat cath is positiv |
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electrolytic cell
molten NaCl is electrolyzed to form? |
Cl2(g) and Na (l)
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oxidation
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what occurs at the anode?
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cathode
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Na+ migrates toward the?
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it floats at the top and can be removed
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where does the liquid sodium end up?
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anode. there they are oxid to Cl2
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Cl- ions migrate towards the?
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anode of an electr cell is considered to be ?
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positive
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why is the anode of an electrolytic cell considered pos?
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its attach to posit pole of battery and attracts anions from the solut
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in an electrolyt cell
Is it the anode or the cathode that attracts anions from the solution? |
anode
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why is the anode of the galvanic cell considered negative?
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bec the spont oxidat react that occurs there is the source of the cells negative charge.
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oxidation occurs at the _____ in galvanic and electrolytic cells
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anode
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CAThode atrracts the CATions
so in a daniel cell, in the copper half cell, what moves towards the cathode? |
the copper II cations
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CAThode attracts the CATions
in a daniel cell, in the __________ half cell, the copper II cations move towards the cathode |
copper
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CAThode attracts the CATions
in electrophoresis, the ____________ charged Amino acids will migrate toward the cathode |
positively charged
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CAThode attracts the CATions
electrophoresis negativ ch AA will move towards the? |
anode
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electrophoresis
_________ move towar cathode _________ move toward the anode |
positiv ch aa - cathode
negat ch aa- anode |
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sometimes when electrolysis is done in aq solut, __________ and not the solute might be oxid or reduc
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water
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in aq NaCl. if it is electrolyzed, H2O migth be reduced at the cathode to prod?
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H2 gas and OH- ions
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aq NaCl water be reduced to H2 and OH- instead of?
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Na+ being reduced to Na (s)
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What can you use to determine the species in a reaction that will be oxidized or reduced?
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reduction potential
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reduction potential is?
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tendency of a species to acquire electrons and be reduced
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reduction potential
the more positive the potential the greater? |
the species tendency to be reduced
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reduct pot
the more ____________, the greater ___________ |
more posit the potent,
greater tend to be reduced |
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reduct potential
___________ the reduct potent, ____________ tendency to be reduced |
more posit the reduct potent,
greater the tendency to be reduced |
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reduct potential
what is the mnemonic? |
A positive potential means more likely to succeed.
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a reduct potent is measured in?
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volts (V)
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a reduct pot is defined relative to?
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a standard hydrogen electrode
(SHE) |
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SHE is?
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standard hydrogen electrode
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SHE has a potent of?
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0.00 volts
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Standard reduction potential Eo is measured under?
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standard condit
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what are standard conditions?
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25 C
1 M conc for each particip ion, part press of 1 ATM for each gas and metals in pure state |
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higer Eo mean?
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greater tendenc for reduct to occur
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lower Eo means?
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a greater tend for oxidat to occur
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a ___________ Eo means a greater tend for reduct to occur
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higher
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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
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to get the oxidat potential of a given half reaction you have to?
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1.the reduct half react has to be reversed.
2. sign of reduct potent has to be reversed |
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standard electromotive force is?
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EMF.
the differ in potential betw the 2 half cells |
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how do you figure out the EMF?
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add the stand reduct pot of the reduc species and the stand oxidat potent of the oxidized species
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t or f
when adding stand potent do not multiply by the number of moles oxid or reduc |
t
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EMF= Eo red + ?
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EMF= Eo red + Eo ox
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a galvanic cell has a ___________ EMF
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positive
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an electrolytic cell has a ____________ EMF
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negative
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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
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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+
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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 |
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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
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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
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a positive ch in G or Gibbs free energy is spont or non spont?
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it is not spontant
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a ch in G that is negat is spont or non spont?
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spont
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How do you determ the spontaneity of a reaction?
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use ch in G
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the maximum amount of useful work produced by a chemical reaction is
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ch in G
or Gibbs free energy |
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electrochem cell the work done is dependent on?
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number of coulombs and the energy available
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electrochem cell
ch in G= |
ch G= -nFEcell
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-nFEcell=?
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ch in G
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∆G= -nFEcell
what is F |
faraday's constant
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∆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
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∆Go= -nFEocell
this means that the react? |
took place under standard conditions
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∆G= -nFEcell
∆G is negative only if? |
EMF is positive
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∆G is ________, when __________ is positive
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negative,
EMF is positive |