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VCE Chemistry > electrochem > Flashcards

electrochem Flashcards

1
Q

what is hydrogen’s oxidation number

A

in non-metals: +1
in metals: -1

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2
Q

oxidation number of oxygen

A

normally: -2
in peroxides: -1
with fluorine: +2

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3
Q

how to explain whether a redox reaction has occured

A

detail whether there has been a change in oxidation number

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4
Q

reduction of dichromate ion

A

6e + 14H+ + Cr2O7 2- –> 2Cr3+ + 7H2O

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5
Q

what type of redox is combustion of a fuel

A

oxidation

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6
Q

reduction of manganese ion

A

5e + 8H+ + MnO4- –> Mn2+ + 4H2O

(different for basic conditions)

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7
Q

direct redox reaction

A

oxidation and reduction occur in the same vessel/ reactants are mixed together

generally results in release of heat

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8
Q

indirect redox reaction

A

reactants are in two separate beakers

electrical nrg produced hw some heat nrg

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9
Q

explanation of ‘no spontaneous reaction’

A

reductant species is a weaker reductant than the conjugate reductant of the oxidant species which is stonger reductant hence no spontaneous reaction will be observed

italics= substitute with chemical species

‘reductant’ can be replaced with oxidant

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10
Q

explanation of ‘no spontaneous reaction’

A

reductant species is a weaker reductant than the conjugate reductant of the oxidant species which is stonger reductant hence no spontaneous reaction will be observed

italics= substitute with chemical species

‘reductant’ can be replaced with oxidant

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11
Q

limitations of predictions in terms of electrochemical series

A

impacted by:
changes in temp
conc higher/lower than 1M
conditions and experimantal design

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12
Q

potential impacts and observations due to limitaions of predictions

A

reaction may not be observed bc too slow
another product may be formed at electrode
different voltage produced

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13
Q

function of membrane in cells

A

transport ions bw electrodes
prevent oxidant and reductant coming into contact
separate the 2 half cells

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14
Q

factors that limit the life of cells

A

corrosion of electrode (be specific which one)
side reactions

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15
Q

oxidation

A

loss of electrons, increase in oxidiation number, loss of hydrogen, gain of oxygen

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16
Q

salt bridge

A

allow flow of ions between two half cells to maintain electrical neutrality of the cell

17
Q

typical problems with using galvanic cells

A
  • a reactant or product is reactive with either water or air -> fire
  • product could react with another reactant or product
18
Q

ESC is only accurate for

A

reactions occuring at standar lab conditions

19
Q

fuel cell

A

fuel is constantly pumped in and electricity is constantly generated

w/a galvanic = fixed quantity of fuel -> generate finite amount of elec

20
Q

electrolyte in fuel cells

A
  • carry current between electrodes by movement of cations to the cathode and anions to the anode
  • complete the circuit allowing the flow of charged particles through the cell
21
Q

electrodes in fuel cell

A

electrodes are porous
-> greater SA for reactions to take place -> reaction can occur at a faster rate and electrode may also contain a cataylst.
-> pores allow reacting gases to access electrolyte

22
Q

solid oxide fuel cell

A
  • solid electrolyte
  • oxide ions = gaseous
    ie O2(g) + 4e- -> 2O2-(g)
23
Q

advantages of fuel cells

A
  • quiet operation
  • high energy conversion efficiency (vs combustion)
  • low running costs
  • low chemical pollution (vs combustion)
  • doesn’t need to be recharged
24
Q

disadvantages of fuel cells

A
  • manufacturing process and materials are expensive
  • electrodes are expensive bc they also have to function as catalysts
  • need reliable, continual supply of fuel
  • distribution, storage and transport of H2 is difficult
25
Q

galvanic vs fuel cells

A

galvanic:
- electrodes are inert or contain reactants/products
- closed system
- operate at lower temperatures
- half cells in separate vessels

26
Q

primary cells

A

non-rechargable cells that convert chemical energy to electrical energy

amount of energy supplied is limited to amount of reactants available

27
Q

secondary cells

A

rechargable electrochemical cells where reactants can be formed from products of discharge reaction

28
Q

factors impacting cell selection

A
  • mass: portable devices -> lightness is a priority hw transport vehicles can accomodate heavier batteries
  • voltage provided ie aqueous electrolytes cannot provide >2V
  • current: greater SA of electrodes -> greater current
  • shelf life: bc some cells may discharge over time without being used
29
Q

factors affecting battery life

A
  • temp: increase temp -> increase rate of deterioration and rate of side reactions that comprimise battery functionality decreasing battery life hw too low temps -> decrease capaicity of batttery -> lower discharge rate and lower electricity supplied
  • if reactants and products detach from electrodes
  • reactants and products are converted into inactive forms via side reactions
  • leakage of electrolyte
30
Q

if concentration of reactants are high and the two reactants have similar electrode potentials, which reactant is oxidised

A

REACTANT WITH HIGHER CONC IS OXIDISED

31
Q

what voltage must be given to a cell during recharge

A

voltage higher than voltage produced when discahrgeing

32
Q

faraday’s first law of electrolysis

A

the amount of any substance dischared at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the cell

33
Q

faraday’s second law of electrolyisis

A

the amount (mol) of any substance discharged at an electrode during electroysis is the reciprical of the charge on the ion

34
Q

best temperature range for the largest number of charge cycles for a lithium-ion battery

A

9-21 degrees

around room temp (~22) and no higher than

35
Q

advantages of batteries over fuel cells

A
  • low maintainence
  • dont need large amounts of fuel
36
Q

what allows a galvanic cell to produce electricity

A
  • 1/2 cell connected via salt bridge completes the circuit and allows e to flow through connecting wire
  • 1/2 cells are separated so e can flow through connecting wire

VCE Chemistry (8 decks)

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