Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

3/4 Chemistry. > Electrochemistry > Flashcards

Electrochemistry Flashcards

(83 cards)

Start Studying
1
Q

oxidation occurs at the

A

anode

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

reduction occurs at the

A

cathode

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

define oxidation

A

-loss of electrons
-increase in oxidation number
-gain of oxygen
-loss of hydrogen

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

define reduction

A

-gain of electrons
-decrease in oxidation number
-loss of oxygen
-gain if hydrogen

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

reductant AKA

A

reducing agent

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

oxidant AKA

A

oxidising agent

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

oxidant undergoes

A

reduction

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

reductant undergoes

A

oxidation

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

How does H oxidation state change

A

+1 in compounds with non metals eg HCl
-1 in compounds with metal hydrides eg NaH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what must the sum of oxidation numbers be

A

in a neutral compound oxidation numbers should sum to zero

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

in a polyatomic ion the oxidation number must

A

sum to the charge of the ion

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

How do oxidation numbers work in compounds without oxygen or hydrogen

A

the more electronegative element has a negative oxidation number, equivalent to what the charge of its ion would be

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

oxygen usually has an oxidation number of

A

-2

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

Fluorines oxidation number is always

A

-1

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

when does oxygen have a different oxidation number

A

-in peroxides it becomes -1 eg. H2O2
-when bonded to fluorine it becomes +2

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

KOHES stands for

A

balance Key element
balance Oxygen using water
balance Hydrogen by adding H+
balance charges by adding Electrons
add States

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

equation for Cr2O72- into Cr3+

A

Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O

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

equation for Mn04- into Mn2+

A

MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

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

Whats a direct redox reaction

A

reactants are directly mixed in a single beaker and a spontaneous reaction occurs which typically releases thermal energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Whats an indirect redox reaction

A

reactants are in two separate beakers and an indirect redox reaction occurs which typically produces electrical energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How do you explain whether a reaction will occur in terms of reductants

A

(reactant species) is a WEKAER REDUCTANT than the CONJUGATE REDUCTANT of the (oxidant species), which is (stronger reductant) hence reaction will/ will not occur

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

How do you explain whether a reaction will occur in terms of oxidants

A

(oxidant species) is a WEKAER OXIDANT than the CONJUGATE OXIDANT of the (reductant species), which is (stronger oxidant) hence reaction will/ will not occur

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

Limitations of predicting using ECS

A

changes in temperature –> reaction may not be observed as the rate of reaction is too slow

Higher/lower concentration than 1M–> another product may form at an electrode OR if concentration too low the reaction may to be observed

Different conditions/experimental design –> different voltage produced

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

When can a weaker oxidant or reductant preferentially react

A

-It is possible when the weaker oxidant/ reductant has concentration greater than 1.0M eg 4-5M
-it is possible when the stronger oxidant/reductant has concentration less than 1M eg 0.01 M

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What are SLC
25 degrees celsius , 100kPa and 1M solutions
26
define galvanic cell
electrochemical cells in which chemical energy from spontaneous redox reactions are converted into electrical energy
27
define anode
negatively charged in galvanic cell where oxidation occurs
28
define cathode
positively charged in galvanic cels where reduction occurs
29
define salt bridge
structure which allows for transfer of ions between two half cells to maintain electrical neutrality of cell and complete the circuit
30
define electrolyte
source of ions which are used to allow for flow of electric charge within a cell
31
define electrode
electrical conductor that is either unreactive or involved in reaction
32
define standard half cell
cells consisting of both members of conjugate redox pair and an electrode at SLC
33
define standard electrode potential
potential of the half reaction (reduction), given in volts, relative to standard H electrode
34
energy conversion is galvanic cells
chemical --> electrical
35
Cations of salt bridge move towards
cathode
36
anions of salt bridge move towards
anode
37
electrons flow from
anode to cathode
38
how to calculate electric potential
E(top in ECS) - E(bottom in ECS)
39
Fuel cell vs galvanic cell
-fuel cell requires constant supply of reactants and electricity is continuously generated whereas in a galvanic cell a fixed amount of fuel is used to generate a finite amount of electricity -fuel cells use porous electrodes whereas galvanic cells use inert or contain reactants/products -fuel cells operate at higher temperatures -fuel cells separate half cells in same vessels whereas galvanic cells have half cells in seperate vessels -Both convert chemical into electrical energy
40
in fuel cells , fuel reacts at ___ and ___ reacts at cathode
anode oxygen
41
function of electrolyte in fuel cell
-allows for movement of charged ions/source of ions which are needed for reaction to proceed -transports H+ or OH- in acidic and alkaline fuel cells respectively
42
function of electrodes in fuel cells
-site of oxidation /reduction -porous, increase SA and rate of reaction -may contain catalysts which lower activation energy and provide alternative reaction pathway -pores allow gases to access electrode
43
how to convert KOHES into alkaline conditions
add OH- to both sides, OH- and H+ cancel out to form water
44
list 3 advantages of fuel cells
-high energy efficiency -fuel flexibility -quiet operation -no need to be recharged -low maintenance due to lack of moving parts -low running costs
45
disadvantages of fuel cells
-infrastructure and manufacturing is expensive -need reliable and continual supply of fuels -difficult to store, transport and distribute H2
46
compare fuel cell and combustion engine
-fuel cells are much more energy efficient than combustion engines because combustion engines require many intermediate steps whereas fuel cells convert chemical directly into electrical energy. -fuel cells can have overall less impacts on environment (because more efficient) -fuel cells more expensive because H very expensive to store and obtain -fuel cells quieter
47
intermediate steps for combustion engines
chemical to thermal to mechanical to electrical
48
Safety problems with hydrogen gas
-highly flammable -colourless, tasteless and odourless so difficult to detect -must be compressed and stored at very low temperatures so expensive
49
When can fuel cells be beneficial to the environment
if the fuel supplied eg hydrogen gas is obtained via renewable resources then there is a negligible change to CO2 levels
50
rechargeable batteries aka
secondary cells
51
primary cells are
used until the supply of reactants run out (not rechargeable)
52
Define memory effect for batteries
some cells have decreased capacity to be fully charged. This occurs when rechargeable batteries are not fully discharged before recharging
53
When do mass of cells matter
in portable devices lightness is prioritised whereas vehicles can often accommodate heavier and bulkier batteries
54
what two reactions do rechargeable cells undergo
discharge and recharge
55
when a secondary cell discharges it coverts ___ into ___ and acts as a ___ cell
chemical electrical galvanic
56
when a secondary cell recharges it coverts ___ into ___ and acts as a ___ cell
electrical chemical electrolytic
57
What are the conditions for a secondary cell to be recharged
-the products of the discharge reaction must stay in contact with the electrodes -a voltage higher than the voltage supplied during discharge is required
58
during recharge the positive terminal of the power supply connects to the ___ an the negative terminal of the power supply connects to the ___
positive electrode negative electrode
59
polarity of electrode during recharge
anode is positive cathode is negative
60
what occurs at anode and cathode in recharge
oxidation at anode and reduction at cathode
61
what dictates the polarity of electrode in recharge
electrons are pushed to the cathode and pulled away from the anode by the power supply therefore reduction at cathode and oxidation at anode
62
define battery life
number of charge/discharge cycles before a battery becomes unusable
63
what factors effect battery life
-high temperatures will deteriorate the cell at a greater rate ,increase the rates of side reactions and compromise the battery's functionality (parts) -low temperatures decrease the electric potential -fluctuations in temperature can also impact battery life -reactants and products may fail to adhere to electrodes -reactants and products may be converted to inactive forms -other chemicals may interfere with internal mechanism of batteries -internal components may corrode -impurities could react with reactants or products -electrolyte may leak decreasing contact between electrodes and electrolyte -memory effect
64
how to increase battery life of rechargeable cells
store batteries at lower temperatures eg 10-15 degrees celsius
65
how to increase the battery life of primary cells
-same principles as secondary cells but could also increase amount of reactants
66
polarities of electrodes in electrolysis
positive anode and negative cathode
67
what type of reactions occur in electrolysis
non spontaneous redox reactions
68
functions of electrolysis
-electroplating -produce reactive metals -electrorefining -recharge of secondary cells -electrolysis of water to produce oxygen and hydrogen gas
69
describe electron movement in electrolytic cells
electrons are pushed to the cathode and pulled away from the anode by the power supply therefore reduction at cathode and oxidation at anode
70
liquid/ molten vs aqueous
aqueous contains WATER
71
energy conversion in electrolytic cells
electrical to chemical
72
in electroplating what is where
-object to be plated at cathode -anode is the metal which will be plate on cathode eg silver metal
73
what ions should always comprise the electrolyte
highly soluble ones eg NO3- or SO42-
74
in electrolysis of water what happens where
at cathode water is reduced to four hydrogen gas at anode water is oxidised to from oxygen gas
75
why is Aluminium dissolved in cryolite
lowers melting point of alumina from 2000 to 1000 degrees celsius approx.
76
cryolite formula
Na3AlF6
77
what is faradays first law
amount of any substance discharged at an electrode during electrolysis is directly proportional to quantity of electrical charge passed through the cell (linear relationship)
78
the greater the charge of the ion the ___ mass deposited on cathode
less because of molar ratios eg 1 mole of electrons will produce 1/2 mole of Mg
79
what is Faradays second law
amount (in mol) of any substance discharged at an electrode during electrolysis is the reciprocal of the charge of ion
80
at which electrode is the impure metal during electrorefining (eg.blister copper)
at the anode
81
onto which electrode does the pure metal collect in electrorefining
the cathode
82
explain the events occuring at the anode during electrorefining
the impure metal(eg. blister copper) is placed at the anode where the strongest reductants are oxidised(metals such as Pb and Ni). the reductants weaker than the metal being refined(eg. Ag, Au and Pt) are not oxidised and hence fall to the bottom of the anode forming a muddy mixture known as anodic sludge.
83
features of daniell(galvanic) cell which allows electrcity production
The two half-cells are separated so that electrons can flow through the connecting wire.  The two half-cells are connected via a salt bridge to complete the circuit and allow electrons to flow through the connecting wire.

3/4 Chemistry. (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions