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IB Chemistry 30 > Electrochemistry, Rechargeable Batteries, Fuel Cells, Photovoltaic Cells and Dye-Sensitized Solar Cells (HL Option C.6 & C.8) > Flashcards

Electrochemistry, Rechargeable Batteries, Fuel Cells, Photovoltaic Cells and Dye-Sensitized Solar Cells (HL Option C.6 & C.8) Flashcards

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1
Q

What is a redox reaction?

A

Reaction where electrons are transferred from the species being oxidized to the species being reduced

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2
Q

What is a battery?

A

A series of electrochemical cells

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3
Q

What is a primary electrochemical cell?

A

cell where the the materials are consumed and the reaction is not reversable

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4
Q

Why can’t primary electrochemical cells not be used anymore?

A

Anode is oxidized and cannot be used, solution becomes polarized which increases build up of hydrogen bubbles on the anode which increases the internal resistance of the cell

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5
Q

What is the main limitation of primary electrochemical cells?

A

They do not operate well under high current demand

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6
Q

What is a secondary cell / rechargeable cell?

A

cell where chemical reactions generate electricity and reactions can be reversed by applying a current

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7
Q

What is the main limitation of secondary electrochemical cells / rechargeable cells?

A

they have a higher rate of self - discharge

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8
Q

Why must cars batteries be toped up with distilled water occasionally?

A

if a cell runs too long it may have an over-voltage, which produced hydrogen and oxygen

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9
Q

What is a lithium ion battery?

A

Battery with a graphite anode with lithium atoms absorbed into the lattice, the cathode is a lithium cobalt

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10
Q

What is the benefit of using lithium in lithium ion batteries?

A

Lithium has the highest oxidation potential and is light weight

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11
Q

What is the electrolyte in lithium - ion cells? Why?

A

a gel polymer of H2SO4, otherwise the lithium is an active metal and would react with the water

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12
Q

What is occurring at the cathode while a lithium - ion cell is charging? (Remember anode/cathode reversed)

A

Li+ + e- -> Li

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13
Q

What is occurring at the anode while a lithium ion cell is charging? (Remember anode/cathode reversed)

A

LiCoO2 -> Li+ + e- + CoO2

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14
Q

What is occurring at the anode while a lithium - ion cell is charging?

A

Li -> Li+ +e-

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15
Q

What is occurring at the cathode while a lithium - ion cell is charging?

A

Li+ + e- + CoO2 -> LiCoO2

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16
Q

What are the advantages of lithium - ion batteries?

A

high charge specific density, can hold charge better than other batteries, can withstand many recharge cycles, contain no heavy metals so they are considered safe for the environment

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17
Q

What are the disadvantages of lithium - ion batteries?

A

sensitive to high temperatures, damaged if allowed to run completely flat, they last only a few years, could explode if overheated or punctured

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18
Q

What is a Nickel - Cadmium battery?

A

Cell with a nickel (III) oxide hydroxide cathode and a cadmium metal anode

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19
Q

What determines the wavelength of light which a conjugated system absorbs?

A

the length of the conjugated system, the longer the system the longer the wavelength of light

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20
Q

What is electron conjugation?

A

The pi - electron clouds of adjacent double bonds partly overlap with one another and form a large cloud of delocalized electrons

21
Q

What is a semi-conductor?

A

materials with electrical conductivity half way between conductors and insulators

22
Q

What influences the conductivity of a semi-conductor?

A

temperature (increases conductivity)

23
Q

What is a photovoltaic cell?

A

cell made of semi-conductors that can absorb photons of light resulting in electrons being knocked free from atoms and creating a potential difference

24
Q

What are elements that are semiconductors, used in photovoltaic cells?

A

usually group 14 (ie. silicon or germanium) , maybe groups 13 or 15 (gallium arsenide)

25
Q

What is an n-type semiconductor?

A

a semi-conductor doped with phosphorus

26
Q

What is a p-type semiconductor?

A

a semi-conductor doped with boron

27
Q

What is the effect of doping a semi-conductor?

A

provides an extra electron which can become mobile with a small potential difference, or a hole that can be used to hold an electron

28
Q

What is a band-gap?

A

gap between valence and mobile electrons

29
Q

What provides power in a photovoltaic cell?

A

a charge separation occurs in the semi-conducts which allows for a one-way flow of electrons, flow of electrons provides electrical power

30
Q

What are nanoparticles?

A

particles with dimensions less than 100nm, exhibit properties that differ from those of bulk material

31
Q

Why are nanoparticles used in DSSCs?

A

increase surface area, helps transfer electrons from the cathode back to the dye molecules

32
Q

Where does oxidized dye receive the electron from? (give equation)

A

3I- -> I3- + 2e-

33
Q

What determines a cell’s internal resistance?

A

ion mobility, electrolyte conductivity, and the electrolyte surface area

34
Q

What is a fuel cell?

A

An electrochemical device which converts chemical potential energy in a fuel to chemical potential energy

35
Q

What are the key components of a PEM fuel cell?

A

the electrolyte / separator, proton exchange membrane, electrodes, bipolar plate

36
Q

What does the electrolyte / separator do in a PEM fuel cell

A

prevents components from mixing

37
Q

What does PEM stand for?

A

Proton exchange membrane

38
Q

What does the proton exchange membrane do in a PEM fuel cell?

A

polymer which allows H+ ions to diffuse through but not electrons or molecules

39
Q

What do the electrodes so in a PEM fuel cell?

A

catalysts which allow chemical reactions to occur

40
Q

What is the role of the bipolar plate in a PEM fuel cell?

A

collects the current and builds up voltage in the cell

41
Q

What occurs at the anode in a PEM fuel cell?

A

H2 -> 2H+ +2e-

42
Q

What occurs at the cathode in a PEM fuel cell?

A

O2 + 4e- -> 2O2-

43
Q

What is the net ionic reaction of a PEM fuel cell?

A

2H2 + O2 -> 2H2O

44
Q

What is an alkali fuel cell?

A

cell which provides water and electricity

45
Q

What are the reactants in a alkali fuel cell?

A

Oxygen and hydrogen gas, and an acidic electrolyte

46
Q

What ion is migrating in an alkali fuel cell (note name)?

A

OH-

47
Q

What is produced from an alkali fuel cell?

A

water and electricity

48
Q

Where is water produced in an alkali fuel cell?

A

anode, opposite in a PEM hydrogen cell

IB Chemistry 30 (7 decks)

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