1
Q
reduction
A
process in which atom/ion gains electrons
2
Q
oxidation
A
process in which atom/ion loses electrons
3
Q
oxidation state
A
a measure of electron possession relative to atom in pure element
4
Q
disproportionation
A
when one substance can be simultaneously reduced and oxidized in the same rxn
5
Q
oxidizing agent
A
being reduced, but causes another species to be oxidized
6
Q
reducing agent
A
being oxidized, but causes another species to be reduced
7
Q
importance of half cell equations
A
rxn divided into 2 simpler rxns (oxidation and reduction) allowing for balance of redox reactions
- emphasize electron transfers that occur during rxn
8
Q
steps to writing half equations
A
- write unbalance half eqn
- balance all atoms (not O or H)
- balance O w water
- balance H w H+(aq)
- balance charges w e-, balance e- and cancel anything on both sides
9
Q
what are redox titrations importance of redox titrations
A
- reaction where both oxidation and reduction occurs
used to determine unknown concentration of substance in a solution
10
Q
colour change in iodine-thiosulfate redox titration
A
- starch is added to iodine to make blue colour
- as I2-> I- the blue colour will disappear, indicating the end point
11
Q
colour change in iron with manganate (VII) redox titration
A
- iron (Fe2+) and manganate (MnO4-) react w each other to make Mn2+ creating colourless solution
- when Fe2+ is all consumed, unreacted manganate will turn solution into faint pink/purple colour
12
Q
how can you deduce if a single displacement rxn is occuring qualitatively
A
- colour change
- solid disappearing or being deposited
- temperature change
13
Q
when are single displacement rxns able to occur spontaneously (metal + non metal)
A
when the reduction agent (metal by itself) is stronger (higher on table 19) than oxidizing agent
14
Q
when are single displacement rxns able to occur spontaneously (nonmetal + nonmetal)
A
- halogens form negative ions -> halogen thats by itself is OA
- in this case, the RA is the halogen attached to another substance and must be higher on T19 than OA
15
Q
2 main types of electrochemical cells
A
voltaic (galvanic) vells - generate electricity from chemical rxns
electrolytic cells - drive chemical rxn using electrical energy
16
Q
voltaic cells
A
converts chemical potential energy to electrical energy from spontaneous redox titrations
17
Q
importance of the standard hydrogen electrode (SHE)
A
- gives baseline for measuring/comparing electrode potentials of other hald cells
18
Q
what is the standard hydrogen electrode (SHE)
A
- inert platinum electrode in contact w 1mol/dm3 hydrogen ions and hydrogen gas at 100kPa
- half cell potential of 0.00V
19
Q
standard electrode potential
A
potential (voltage) of the reduction half equation under standard condition relative to the SHE
20
Q
what are the standard conditions needed to measure standard electrode potential
A
- all solution conc. are 1.0mol/dm3
- all gases at pressure of 100kPa
- all substances are pure
- temp is 298K
- if the half cell is not a solid metal, platinum is used as electrode
21
Q
standard half cells
A
half-cells under standard conditions
22
Q
features needed to find standard electrode potential of half cell
A
- SHE linked to standard half-cell thru external circuit w voltmeter
- salt bridge to maintain ion flow
- electromotive force (EMF) will be generated (shown on voltmeter) which is the stan. elec. pot.
23
Q
positive vs. negative value of standard electrode potential (Eθ)
A
half-cell has greater tendency to be reduced (stronger OA) compared to H+ vs. has lower tendency
24
Q
reactions in voltaic and electrolytic cells are spont/non-spont
A
v: spontaneous
e: non-spontaneous
25
where do the ox/red rxns occur in voltaic cells
- in half cells in different containers
26
the electrode where oxidation occurs is ____, the electrode where reduction occurs is ______
anode, cathode
27
electrolyte
a solution of the metal electrode (ex. Cu=electrode, Cu2+=electrolyte)
28
how does potential difference show if a rxn is spontaneous
if ▵Eθ=+, ▵Gθ=-, the reaction is spontaneous
if ▵Eθ=-, ▵Gθ=+, the reaction is non-spontaneous
if ▵Eθ=0, ▵Gθ=0, the reaction is at equilibrium
29
where does oxidation and reduction occur in voltaic vs electrolytic cells
v+e: oxidation at the anode, reduction at the cathode
30
polarity of anode and cathode in voltaic vs electrolytic cells
v: - at anode, + at cathode
e: + at anode, - at cathode
31
direction of electron movement in voltaic vs electrolytic cells
v: - anode -> +cathode
e: +anode -> - cathode
32
fuel cells
type of primary cell that converts combustion rxns (chemical energy) into electrical energy
33
difference bw voltaic and fuel cells
v: finite quantity of reactants, production of electricity stopped when reactants consumed
f: reactants continuously supplied from external source, infinite production of electricity
34
how do hydrogen fuel cells work
- H2 supplied to anode, O2 supplied tp cathode
- proton exchange membrane (PEM) selectively allows H+ ions to diffuse bw cat. and anode
- H(g) oxidized at anode on surface of platinum based catalyst
- electrons leave from prev. oxidation thru external circuit to produce electrical output
- protons formed move across PEM to cathode, reducing O2 to form water as waste
35
are hydrogen fuel cells clean
- considered to be as only product is water -> but hydrogen is not abundant, its production can be bad for environment
36
2 ways hydrogen can be produced for hydrogen fuel cells + impact
1. electrolysis of water (using electricity to split water) <- can be powered by renewable sources of energy
2. steam-reforming of hydrocarbons (produces CO + H(g) however CO is toxic and can create CO2)
37
direct-methanoic fuel cell (DMFC) vs hydrogen fuel cell
- in DMFC, methanol is used in place of H(g) to produce H+ -> can be produced thru fermentation = less impact on environment
38
pros and cons of primary general cells
p: inexpensive, light weight, good shelf life
c: only be used once, battery->landfill=bad, only delivers small currents
39
pros and cons of primary fuel cells
p: more efficient than direct combustion, not pollution if hydrogen is fuel
c: hydrogen = risk of explosion, very expensive, stored/transported in large containers, only delivers small currents
40
pros of secondary/rechargeable general cells
p: materials can be regenerated, can deliver high current
41
pros and cons of secondary/rechargeable lead-acid batteries
P: can deliver large amounts of energy over short periods
c: heavy mass, lead and sulfuric acid are pollutants
42
pros and cons of secondary/rechargeable cadmium/nickel batteries
p: longer life that lead-acid batteries
c: cadmium=toxic, low voltage, very expensive
43
pros and cons of lithium-ion batteries
p: low lithium density, high voltage, no toxic heavy metal
c: expensive, limited lifespan
44
why are the rxns in primary voltaic cells irreversible
- polarization occurs and consumption of rxn materials
45
how are the rxns in secondary voltaic cells reversible
- can apply electric current to battery to recharge it
46
what is a battery
a series of 2+ electrochemical cells, typically in a single container
47
lead-acid batteries, where are they found, how are they used
type of rechargeable (secondary cell) battery found in gas powered vehicles
- electrical E from batter powers the motor to start engine and electrical sys. in car
48
how are lead-acid batteries recharges
some of the chem. E from combustion in engine is used to reverse chem. rxn that occur during discharge, recharging battery
49
what is battery discharge
the releasing of stored electrical E to power a device
50
what is a lead-acid battery made up of
lead anode, PbO2 cathode, dilute H2SO4
51
lithium ion battery, where are they found
- secondary cell that powers electric vehicles
52
what is a lithium-ion battery made up of
anode: lithium atoms in a lattice of graphite electrodes
cathode: lithium-cobalt oxide complex
- battery medium must be completely non-aqueous
53
electrolysis
process by which electrical energy is used to drive a non-spontaneous chemical rxn
54
what is an electrolytic cell composed of
a single container, 2 electrodes (anode and cathode), a solution (electrolyte), a battery(considered as electron pump)
55
electrolyte
a liquid, usually a molten ionic compound or an aqueous solution of an ionic compound
56
how do electrolytic cells work
- electric current is passed thru and redox rxns occur at electrodes -> removes charges of ions -> forms electrically neutral products
- ions are discharged during process
57
how does the electrolysis of molten salts work
- in solid state, salts dont conduct electricity as ions are in rigid lattice
- when molten, they conduct thru the movement of ions
58
what factors affect the products formed from electrolysis of aqueous solutions
- relative Eθ values of ions
- relative concentration of ions in electrolyte
- nature of electrode (inert vs. active)
59
considerations for the electrolysis of aqueous solutions
- water is always competing to be oxidized/reduced
- ox/red with Eθ closer to 0.00 will be preferred (selective discharge)
60
electrolysis of aq solutions - where is H2O oxidized and reduced
cathode: H2O is reduced to H2
anode: H2O is oxidized to O2
61
electrolysis of water
splitting of water into hydrogen and oxygen gases
- needs another ionic compound to increase conductivity of water but wont interfere w dishcharge of ions (NaOH, or H2SO4)
62
how to determine preferred rxn in different concentrated aq solutions
- if conc. <25% (dilute), water is preferred
- if conc. >25% (concentrated), other ion is preferred
63
importance of electrolysis of aq sodium chloride brine in industry
- valuable to produce both chlorine gas and sodium hydroxide
- brine is important as it makes Cl- the preferred rxn, producing Cl2 gas
64
cell notation/cell diagram
electrode|electrolyte || electrolyte|electrode
-> follows anode -> cathode
65
charging reaction
the chemical processes that occur when a rechargeable battery is being charged
- chemical rxns are reversed versions of discharge rxn
66
what are the products of the electrolysis of water
H2O--> 1/2O2 + H2
67
electroplating
process where electrolysis is used to deposit a thin layer of one metal on top of another
68
features of an electrolytic cells used for electroplating
- electrolyte containing metal ions which are to be deposited
- cathode is object to be plated
- sometimes anode is made of same metal that is to be coated
69
why is the anode sometimes the same metal that is to be coated in electroplatin
it can be oxidized to replenish the supply of ions in the electrolyte at the same rate in which ions are being reduced at the cathode
70
factors that affect amount of product in electrolysis
- quantity of electric charge passed
- charges of ions (mole ratio)
71
formula to find electric charge (Q)
Q=It
72
formula to find moles of electrons
ne-=Q/F
73
2 ways that current in conducted in an electrolytic cell
electrolyte (solution): positive ions attracted to cathode (-) and negative ions attracted to anode (+)
conductors (external wire): electrons flow from negative pole of battery to positive pole
74
why is the electrolysis of NAOH and H2SO4 both referred to as the electrolysis of water
- both form 2:1 ratio of H2:O2
- pure water is a poor conductor, ions cause water to conduct
75
what is the EMF
- electromotive force
- voltage that battery can generate with no current flowing
- difference in Eθ at cathode and anode
76
what do positive standard reduction potentials mean? negative?
p: substance easily gains e- (reduced) and acts as a strong OA
n: substance resists gaining e-, loses them (oxidized) and acts a strong RA
77
overall equation in lithium ion battery
Li(s) + CoO2(s) -> LiCoO2(s)
78
