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A-LEVEL CHEM > electrochemical cells > Flashcards

electrochemical cells Flashcards

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1
Q

What is a half cell?

A

half an electrochemical cell, made up of an electrode (platinum or using the metal itself) in a solution containing aqueous ions

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2
Q

What makes up an electrochemical cell?

A

2 half cells
salt bridge
voltmeter
wire

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3
Q

What does the salt bridge contain?

A

KNO3/NaNO3

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4
Q

What is the role of the salt bridge?

A

allows the transfer of ions/charge

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5
Q

What is the electrode potential of a cell?

A

a value that tells us how easily the half cell is to be oxidised

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6
Q

What will the most negative half cell undergo?

A

oxidation

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7
Q

What will the most positive half cell undergo?

A

reduction

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8
Q

whats SHE

A

Standard Hydrogen Electrode
used as a reference for electrode potential values

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9
Q

What is the set up of the SHE?

A

Pt electrode
1mol dm3 H+ ions in solution
298K
100kPa

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10
Q

What are the standard conditions for electrochemical cells?

A

100kPa
298K
1 mol dm-3 ions

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11
Q

What is the function of the porous separator in a chemical cell (battery)?

A

salt bridge - allows transfer of ions

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12
Q

What happens to the chemical reaction when a cell is recharged?

A

it is reversed

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13
Q

Why are some chemical cells non-rechargeable?

A

reaction cannot be reversed
reaction produces a gas

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14
Q

Why does the metal case of some chemical cells break down over time?

A

the metallic case is a reactant and gets used up

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15
Q

What happens to cell emf over time?

A

decreases as reactants get used up

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16
Q

Which half cell is on the left?

A

half cell with most - electrode potential

17
Q

What is the equation showing the positive electrode in a lithium ion cell?

A

Li+(aq) + CoO2(s) + e- –> Li+CoO2- (aq)

18
Q

What is the equation showing the negative electrode in a lithium ion cell?

A

Li(s) –> Li+(aq) + e-

19
Q

What is the standard cell representation for a lithium ion cell?

A

Fe / Li+ / Li // Li+ / CoO2 / Li+CoO2- / Fe

20
Q

What is the discharge equation for a lithium ion cell?

A

Li (s) + CoO2 (s) –> Li+CoO2- (aq)

21
Q

What metals make up a Daniell cell?

A

Zn and Cu

22
Q

How is cell emf calculated from electrode potentials?

A

right - left

23
Q

What is an electrochemical series?

A

list of electrode potentials in numerical order

24
Q

What is one property a salt bridge MUST have?

A

must not react with the electrolyte/ions in solution

25
Q

Why would a salt bridge containing a carbonate ion not be suitable for use (when H+ is present)?

A

carbonate ions will react with acid

26
Q

What are 2 advantages of using Hydrogen Fuel Cells compared to using hydrogen in combustion?

A

HFCs:
- less energy wasted as thermal energy
- reaction happens at low temperatures

27
Q

What are the half equations for a hydrogen-oxygen fuel cell operating in alkaline conditions? Use these half equations to explain how an electric current can be generated

A

O2 + 2H2O + 4e- ⎯→ 4OH-
H2 + 2OH- ⎯→ 2H2O + 2e-
Oxygen electrode gains electrons (is reduced), hydrogen electrode loses electrons (is oxidised)

28
Q

Why does a hydrogen fuel cell does not need to be recharged?

A

emf is constant (given that supply of reactants is constant)

29
Q

What is one major hazard associated with the use of a hydrogen–oxygen fuel cell in a vehicle?

A

hydrogen is flammable/ explosive

30
Q

What would happen to the cell emf if the surface area of the electrodes was increased?

A

no change / nothing

31
Q

What are the advantages of using hydrogen fuel cells?

A

-constant emf as long as reactant supply is constant
-works at room temperature so low thermal energy loss (compared to burning hydrogen)
-produces H2O as by-product, no greenhouse emissions or other pollutants such as NOx, SO2 (be specific)

32
Q

What are the disadvantages of using hydrogen fuel cells?

A

-little hydrogen infrastructure in place (petrol stations)
-production of H2 currently energy intensive (produces greenhouse gases in power stations)
-storage of hydrogen is difficult and dangerous (explosive gas)

33
Q

what do you do to most negative half cell

A

flip equation

34
Q

wheres oxidising agents in table

A

left hand side

35
Q

wheres reducing agent in table

A

right hand side

36
Q

strongest oxidising agent and weakest reducing agent

A

most + sep

37
Q

weakest oxidising agent and strongest reducing agent

A

most - sep

38
Q

e cell equation

A

reduced - oxidised
positive - negative
right-left

39
Q

when is pt electrode used

A

2 non metal half cells used

A-LEVEL CHEM (62 decks)

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