Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemistry 3/4 > electrochemistry > Flashcards

electrochemistry Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

secondary cell examples

A

lead acid accumulator, nicad cell, nimh cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

discharge

A

conversion of chem energy to electrical as a result of a spontaneous reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

secondary cells

A

rechargeable cells or accumulators
- when secondary cell discharges acts as a galvanic cell which converts chemical energy to electrical energy
- when cell is recharged it will act as an electrolytic cell and electrical energy is converted to chemical energy - will require voltage for reaction bc non spontaneous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what must happen for a secondary cell to be recharged

A

-products of the discharge must remain in contact with the electrodes
-voltage higher than voltage produced in discharged is required

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is positive terminal connected to in recharge

A

the positive terminal of cell connects to positive terminal of power supply

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

recharging 2dary cells polarity

A

cathode is negative while anode is postitive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

discharge - galvanic cells polarity

A

anode is neg and cathode is pos

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

NiCd battery discharge

A

oxidation- Cd+2OH- -> Cd(OH)2 + 2e-
reduction - NiO(OH) + H2O + e- -> Ni(OH)2 + OH-

recharge will be the other way around

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

lead acid battery

A
  • secondary cells used in car and truck batteries
  • need 12 V above total potential
  • product of the discharge is PbSO4 which forms a solid on electrodes and allows battery to be recharged
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

lead acid battery discharge oxidation

A

anode oxidation
Pb+ H2SO4 -> PbSO4 + 2H+ + 2e-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

lead acid battery discharge reduction

A

PbO2 + H2SO4 + 2H+ + 2e- -> PbSO4 + 2H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

battery life

A
  • used to describe battery cell performance
  • technical specification of battery life refers to number of charge and discharge cycles before a battery becomes unstable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

temp affect on battery life

A

temperature
- increase temp will mean battery deteriorates quicker
- as temp increases ROR of side reactions increase and decrease battery life
-temp decrease capacity of battery decreases and cell ROR decreases - less energy generated (electrical)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

battery life factors

A

-reactants and products ay become detached from their electrodes
- reactants and products may be converted into inactive forms through side reactions
-corrosion of internal components
- leakage of electrolyte solution
-impurities in cell could react with products or reactants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

self discharge

A

loss of electrical capacity of a battery due to deriation of battery components
- caused by side reaction , low temp and slow ROR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how can battery life be improved for non rechargeable cells

A

increase amount of _______ present
reduce SA of ___ anode and____cathode
store at consistent temp - avoid high temp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

NiMH cells

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

electrolysis

A

electrical energy is converted to chemical energy via a nonspontaneous reaction using a power source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are some uses of electrolysis

A
  • convert ions into metals
    -produce reactive materials eg aluminium and sodium
  • electrorefining - purifying metals
  • recharging secondary cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

electrolysis

A
  • ox at the positive anode
    reduction at the negative cathode
    anode to cathode electrons move
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what does the external power source do

A

it will force the reaction to occur - will force the ions to seperate
- external power source pushes electrons to cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what state is molten

A

liquid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

comparing molten with aqueous

A

molten will just seperate the ions but the aqueous also has water ( competition at the electrodes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

why is there a barrier or seperator in electrolysis

A

so the products and ions will not react with each other and will not interfere in the half cell reactions - allows for a spontaneous reaction to occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what will react at the electrodes in electrolysis

A

strongest oxidising agent is reduced at cathode
stronger reducing agent is oxidised at anode
can be water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

in a galvanic cell why must the reactants/ half cells be seperated

A

they do not want to have a direct reaction because it will reduce electrical energy generated and will produce thermal energy - need indirect to produce electricity and a voltage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is needed for electrolysis of water

A

an electrolyte eg . KNO3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

electrolysis of water equation

A

2H2O -> 2H2 + O2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

electrolysis of water

A
  • electrolyte KNO3 or other is added in low conc
  • cathode becomes basic and anode becomes acidic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what are safety considerations of OH-

A

it is caustic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what are the safety implications of H+

A

corrosive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

safety considerations of electrolysis of water

A

-H2 is flammable - keep away from naked flames
-H2 is hard to detect leaks - need detectors
- H2 is highly reactive - wear safety equiptment and store at high pressures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

electroplating

A

application of electrolyisis when metal ions are reduced to form a solid metal coating on an object

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what is being plated in electroplating

A

the cathode - it will gain ions from the anode to form solid metal coating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what is the polarity of where the deposits are in electroplating

A

negative because it is at the cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

why is it deposited at the cathode

A

when cell is electrolysed the cathode is negative. the positive cations will move toward the cathode and they will be reduced to formed the metal which will coat the desired substance.

37
Q

downs cell - what is it used for ?

A

it is used for production of sodium metal by using molten sodium chloride

38
Q

down cell equations

A
  • the Cl is oxidised
  • the Na is reduced
39
Q

why is a carbon used instead of other electrodes

A

it is inert and will not participate or interfere with the reaction

40
Q

why is cryolite added

A

decrease the MP required - energy and cost effective

41
Q

aluminium production - hall heroult process

A

Al2O3 is dissolved in cryolite which lowers MP
anode - C + 2O(2-) -> CO2 + 4e-

42
Q

cryolite formula

A

Na3AlF6

43
Q

membrane cell - use?

A

used to produce sodium hydroxide and generate both chlorine and hydrogen gas

44
Q

brine

A

concentrated salt solution eg . NaCl - must be 5M or higher

45
Q

why is a porous electrode used

A

it will increase surface area, increase rate of reaction and increase effectiveness of membrane cell

46
Q

membrane cell - half cell reactions

A

ox - Cl- is oxidised to Cl2
red - H2O is reduced to H2 gas and hydroxide ions

47
Q

electrorefining - purification

A
48
Q

why are fuel cell electrodes expensive

A

they are porous
formed from high quality metals

49
Q

how to improve battery life

A

-store at consistent temps and avoid high temps
-increase amount of reactants present
-reduce surface area of anode and cathode so longer lasting

50
Q

safety measures / guidlines

A
  • keep away from naked flames
  • wear safety equiptment - lab coat, glasses, dilute spills
  • use a fume cupboard
51
Q

what are similarities with galvanic and electrolytic cells

A

oxidation still at anode
reduction still at cathode

52
Q

difference (5) bw galvanic and electrolytic cells

A
  • in g the anode is negative while in e the anode is positive
  • in g the cathode is positive while in e the anode is positive
  • g is a spontaneous reaction while e is a nonspontaneous reaction
  • in galvanic the half cells are indirect while in e they are not seperated into diff vessels
  • g converts chemical energy to electrical while e will convert electrical to chemical energy
53
Q

when electroplating occurs does conc of metal change

A

no. molar ratios of reduction and oxidation equations are the same, so concentration remains constant. the metal ions used must be a stronger oxidant than water

54
Q

features in electrolytic cell

A

their must be two conductive ekectrodes, electrolyte to be used to allow flow of ion, a power supply

55
Q

limitations of ESC

A

-only applies to reactions in aq. sols
-can only apply to SLC
-does not provide indication of reaction rate
-does not tell us if a precipitate is formed

56
Q

oxidation occurs at the

A

anode

57
Q

reduction occurs at the

A

cathode

58
Q

salt bridge

A

a soluble strip which will allow cations and anions and spectator ions to flow
- maintains the cell neitrality
- completes internal circut

59
Q

cations move to the

A

cathode

60
Q

anions move to the

A

anode

61
Q

oxidation

A

the loss of electron
- will increase oxidation number , lose H and gain O

62
Q

reduction

A

gain of electrons
(reactants side )
- will decrease oxidation number , gain H, lose O

63
Q

reductant

A

it will undergo oxidation
- it will cause reduction by donating the electrons

64
Q

oxidant

A

it will undergo reduction
- it will accept electrons and cause oxidation

65
Q

direct

A

when the reactants ad products reaction will be within the same vessel so can interact with one another directly spontaneously - will release thermal energy

66
Q

indirect

A

will use seperate vessels to ensure half reactions can occur and will produce electrical energy

67
Q

does indirect produce moanily thermal energy

A

no it does not . it will produce electrical energy

68
Q

observing a redox reaction

A

the reaction rate may be too slow to observe , other side reactions might occur , colour changes or change in mass of electrode

69
Q

galvanic cell

A

when chemical energy is converted to electrical energy via an indirect spontaneous reaction

70
Q

function of the electrolyte

A

it is a source of cations and anions for both ahlf cells and will allow for a flow of ions in order to maintain cell neautrality

71
Q

electric potential equation

A

E cathode/ pos - E anode/ neg = ____V

72
Q

acidifed permanganate equation

A

Cr2O(2-)7 + 14H+ -> 2Cr(3+) + 7H2O

73
Q

MnO4(-) -> Mn(2+)

A

MnO4(_) + 8H+ + 5e -> Mn(2+) + 4H2O

74
Q

reductant - non spontaneous reaction explanation

A

reductant species is a weker reductant than conjugate reductant of oxidant , stronger reductant -> no spontaneous reaction

75
Q

oxidant - explanation why non spontaneous reaction occurs

A

oxidant species is a weaker oxidant than conj oxidant of reductant which is stronger oxidant -> non spontaneous reaction

76
Q

limitations of ESC

A

diff voltage, reaction may be too slow, another product may form

77
Q

ESC predictions are impacted by

A

changes in temp , concentrations differing from 1M, conditions

78
Q

fuel cells

A
  • a type of galvanic cell
  • chemical to electrical energy
  • continuous supply of reactants
79
Q

WHAT ALWAYS HAPPENS AT FUEL CELL

A

fuel is at anode and O2 is always at cathode

80
Q

electrolyte

A

allows movement of charged ions - allows redox to occur

81
Q

does galvanic cell have finite capcaity

A

yes … not a continuous supply of reactants

82
Q

electrodes in fuel cells

A

porous , increase SA , increase ROR
- may also have catalyst

83
Q

advantage of fuel cells

A

high energy conversion efficiency because direct reaction and less energy transformations , fuel flexibility, constant supply of reactants,

84
Q

disadvantage of fuel cells

A

need continual supply of fuel , more expensive to operate and get porous electrodes , difficult to transport gases etc.

85
Q

similarities bw galvanic and fuel

A

both convert chemical to electrical energy

86
Q

difference bw g and fuel cells

A
  • porous electrodes at f while inert electrodes or contain reactants/products
  • ongoing supply of reactants at f while limited supply in g
  • high temps f while g is at low temps
  • half cells in sperate vessels g while fuel cells have same vessel
87
Q

factor impacting cell selection

A

initial and operating cost, size and shape, mass, memory effect, voltage provided, current, shelf life , ease of disposal , environment concerns

88
Q

examples of primary cells

A

alkaline, lelanche, zinc air or silver oxide button cell

89
Q

KOHES IN BASIC AND ACIDIC

A

acidic - H+
basic - OH-

chemistry 3/4 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions