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al. ocr chemistry > electrochemistry and cells > Flashcards

electrochemistry and cells Flashcards

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1
Q

standard conditions for measuring electrode potential (3)

A
  • conc. of solutions = 1.0 mol/dm3
  • 298K
  • 100kpa / 1atm
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2
Q

standard cell for comparison (primary)

- electrode used

A

hydrogen cell

- platinum

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3
Q

metal dipping into solution =

A

half cell

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4
Q

if eq. lies to the left, charge will be … due to … making the potential …

A

negative
due to build up of electrons on metal
negative

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5
Q

if eq. lies to the right, charge will be … due to … making the potential … ??

A

positive
as electrons used up to form the metal
positive

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6
Q

more reactive metals tend to have ….. potentials

A

negative

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7
Q

positive potential = … hand electrode = ….

A

right

cathode

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8
Q

emf of cell =

A

E right - E left

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9
Q

secondary standard

A

one which has been calibrated against primary standard

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10
Q

anode…

A

oxidation

negative

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11
Q

which way do reduction reactions go

A

left to right

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12
Q

which what type of reaction is the more negative V

A

oxidation

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13
Q

which way do oxidation reactions go

A

right to left

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14
Q

what is always needed for fuel cells?

- what can be used?

A
  • oxygen!!

- hydrogen/alternatives

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15
Q

set up used to investigate potential of an electrode

A
  • use standard hydrogen electrode

- salt bridge - potassium nitrate

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16
Q

for a positive potential difference, electrons moe from…. to …

A

left

right

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17
Q

zinc-carbon cell - features

A
  • cheap
  • non-rechargable
  • fairly short life
18
Q

alkaline cell features

A
  • higher cost then zinc-carbon

- longer life “

19
Q

lithium ion cell features

A
  • rechargable

- used in phones, computers etc.

20
Q

lead acid battery features

A
  • made of 6 cells

- used in cars

21
Q

how are fuel cells different to other cells?

A

continuous supply of chemicals into the cell, so neither run out or need recharging

22
Q

fuel =

A

something that reacts with oxygen to release energy

23
Q

most common methods of producing H2

A
  • electrolysis of sea water

- methane + steam

24
Q

benefits of hydrogen-oxygen fuel cells (3)

A
  • only waste product is H2O
  • efficient
  • dot need recharging
25
Q

cons of hydrogen-oxygen fuel cells (4)

A
  • needs constant fuel supply
  • hydrogen = flammable and expensive
  • H2 production usually involves fossil fuels
  • high cost of cell
26
Q

voltaic cell =

A

connecting 2 half cells together

27
Q

why must 2 different half cell species be kept separate?

A

otherwise electrons would flow in uncontrolled way and heat energy produced instead of electrical

28
Q

electrode with MORE reactive metal will … electrons and is ….. making it the ….

A

loose
negative
anode

29
Q

standard electrode potential =

A

tendency to be reduced and gain electrons

30
Q

limitations of predictions using standard electrode potentials (3)

A
  • rate of reaction - large activation energy - doesn’t give indication of rate
  • concentration - will affect, not all cells have 1.0 mol/dm3
  • conditions may vary
31
Q

what are electrodess in hydrogen fuel cel made from

A

platinum

32
Q

overall reaction for the hydrogen-oxygen fuel cell

A

2H2(g) + O2(g) → 2H2O(g)

33
Q

what happens to the metal in a cell with the MORE POSATIVE electrode potential

A

is REDUCED and GAINS electrons

34
Q

positive electrode is one with

A

lowest standard electrode potential

35
Q

standard cell potential (eq)

A

Eθcell = Eθright half-cell − Eθleft half-cell

36
Q

why is a high resistance voltmeter used to measure electrochemical cells?

A
  • prevents current flowing through circuit
  • if current flowed, reactants would be used up at both electrodes
  • E cell would then decrease
37
Q

the more negative the E°, the further the eq lies to the …

A

LEFT

38
Q

the more positive the E°, the further the eq lies to the …

A

RIGHT

39
Q

why must chemicals in a cell be kept separate

A

otherwise electron flow would be uncontrolled and heat energy would be produced instead of electrical

40
Q

standard electrode potential

A

emf of half cell when connected to a standard hydrogen half-cell under standard conditions

41
Q

limitations of predictions using Eθ values

A
  • no indication of rate
  • measured using 1 mol/dm3 conc - if conc higher then standard the value will be different
  • actual conditions will be different from standard conditions
  • standard electrodes apply to AQUEOUS equilibria - many reactions aren’t aqueous
42
Q

3 types of cell

A
  • primary
  • secondary
  • fuel

al. ocr chemistry (20 decks)

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