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electrochemistry Flashcards

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1
Q

redox reaction

A

a reaction involving the transfer of electrons

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2
Q

oxidation

A

loss of electrons

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3
Q

reduction

A

gain of electrons

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4
Q

oxidising agent

A

substance that accepts electrons
(is reduced)

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5
Q

reducing agent

A

substance that donates electrons
(it is oxidised)

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6
Q

spontaneous redox reaction

A

self sustaining
stronger reactants preferentially

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7
Q

non-spontaneous redox reaction

A

does not happen on its own
2 relatively weak agents
requires potential

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8
Q

galvanic cell

A

electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy
has capacity to deliver current until rxn reaches eqm or has run to completion - voltage of cell = 0

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9
Q

cathode

A

electrode where reduction takes place
(RED CAT)
plating

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10
Q

anode

A

electrode where oxidation takes place

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11
Q

anode

A

electrode where oxidation takes place

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12
Q

function of salt bridge

A

completes circuit (allows ions to flow)
maintains electrical neutrality in half cells

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13
Q

cell notation

A

anode metal | anode soln || cathode soln||cathode metal

or RA reactant| RA product || OA reactant | OA product

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14
Q

electrolyte

A

substance that can conduct electricity due to the presence of free (mobile) ions when molten or dissolved in solution (in salt bridge)
KNO3 (aq ) - strong,very soluble - no precipitate
also KCl, AgNO3, NaCl
slower slay bridge will slow down rxn- lower current

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15
Q

choosing electrodes

A

inert - Pt
conductive non metal - graphite

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16
Q

Standard electrode potential

A

indication of pos of eqm
more negative - eqm lies left
more positive- eqm lies right

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17
Q

standard conditions

A

temp of 25 degrees celsius (room temp)
concentration of ion soln- 1 mol.dm-3
gas pressure of 1 atm

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18
Q

calculating emf

A

Ecell = Ecathode - Eanode
OR
Ecell= Eoxidising agent - Ereducing agent

pos,big gap- spontaneous rxn
neg,small gap- non-spontaneous

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19
Q

standard hydrogen electrode

A

reference electrode
connected as anode (may not spontaneously act as anode)
written as anode in cell notation
ie Pt| H2 | H+
neg emf will indicate that rxn does not occur spontaneously in direction given in cell notation

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20
Q

SHE connected as and reacted as anode

A

Voltmeter +
notation shows spontaneous rxn
H2 (g) is stronger reducing agent
spontaneous e- flow

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21
Q

SHE connected as and reacted as anode

A

Voltmeter +
notation shows spontaneous rxn
H2 (g) is stronger reducing agent
spontaneous e- flow
E - pos

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22
Q

SHE connected as anode BUT reacting as cathode

A

voltmeter -
notation non spontaneous
hydrogen ions bring reduced
E neg
non spontaneous e- flow
rxns must be written spontaneously

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23
Q

emf

A

indicates how close system is to reaching eqm
max- far
low- close
zero- at eqm

24
Q

LCP and emf

A

increase [reactants] or decrease [products] - fwd favoured - emf increased
decrease [reactants] or increase [products] - rvs favoured - emf decreased
increase in temp favours endothermic rxn (rvs rxn) - decreased emf
decrease in temp favours exothermic rxn (fwd rxn) - increased emf
as anode metal is oxidised , anode ions increase - LCP- favour rxn to use - rate of reduction favoured - eqm shifts right -E more positive
as cathode ions reduced , ion concentration decreases - LCP -favour production - rate of oxidation favoured - eqm shift left
E more neg

25
Q

if factors change in way that oxidation at cathode and reduction at anode favoured

A

emf decreases

26
Q

if factors change in way that oxidation at anode and reduction at cathode favoured

A

emf increase

27
Q

internal resistance

A

opposition to the flow of charge through electrodes and electrolytes in a cell

28
Q

increased surface area of electrodes …

A

increases rate of rxn by lowering internal resistance and increasing max current that cell can deliver (does not affect emf of cell )

29
Q

wider shorter or more conductive salt bridge

A

lowers internal resistance and increased max current cell can deliver (does not affect emf of cell )

30
Q

rate changes

A

no effect on pos of eqm - no impact on emf

31
Q

faradays constant

A

q =nF
mole ratio applies to e-
if no of moles of e- is determined - faradays constant can be used to determine quantity of charge
can link to q=It once moles of e- have been converted to charge

32
Q

electrolytic cells

A

electrochemical cell that uses electrical every four cause a non spontaneous redox reaction to occur ,thus, electrical every is converted into chemical energy.
consists of 2 inert electrodes dipped into electrolyte , DC supply, e- flow from neg terminal of battery to electrode, pos and neg ions carry CURRENT through electrolyte, e- glow from second electrode back to battery

33
Q

electrolysis

A

when electricity flows through molten state or through soln containing ions and ions undergo chemical rxn

34
Q

types of substances that undergo electrolysis

A

ionic salts in soln
molten ionic salts
aqueous solns

35
Q

identifying cathode in electrolytic cell

A

electrode connected to negative terminal becomes negatively charged
pos. charged ions will be attracted to neg. charged electrode where ions gain electrons (due to repulsion from cell) - thus being reduced therefore CATHODE
typically plating

36
Q

identifying anode in electrolytic cell

A

electrode connected to pos. terminal of cell - positive electrode
negative ions attracted - ions will lose e- due to attraction - thus oxidised
ANODE
typically bubbles

37
Q

Cu colour

A

blue

38
Q

MnO4- colour

A

purple

39
Q

Cr207, colour

A

orange

40
Q

Cr3+ colour

A

green

41
Q

Cl2 colour

A

pale green

42
Q

Br2 colour

A

orange / brown

43
Q

I2 colour

A

purple

44
Q

I2 colour

A

purple

45
Q

S colour

A

yellow

46
Q

identify predominant reactions at electrodes in electrolysis of aqueous soln

A

the specific half cell reactions that will occur during electrolysis are those with the smallest difference in their standard electrode potentials
- the ones with the closest E values will take place bcus they require less energy to drive the non spontaneous rxn

47
Q

role of concentration in predicting predominant anode half rxn during electrolysis

A

dilute soln- inherent reactivity will determine which half reaction occurs at anode as it would oxidise innately faster
concentrated soln- increased concentration of ions - favour rxn to use them- increasing rate - adjusting that electrode potential

48
Q

under which circumstances will anode be oxidised in preference to ions in soln

A

relative strengths of reducing agents determine which reaction predominates

49
Q

brine

A

concentrated sodium chloride soln

50
Q

best conductor

A

largest current

51
Q

non electrolyte

A

no current - no products

52
Q

elements that don’t plate

A

weaker oxidising agents than water ( above water on left- Mn2+ upwards )

53
Q

metals above Cu in electro refining of copper

A

stronger reducing agents than cu
will be oxidised and form
ions in soln
weaker oxidising agents than Cu
ions will remain in soln

54
Q

metals below Cu in electro refining of copper

A

weaker reducing agents - won’t be oxidised- remain as unreacted metal
falls off anode as it is eroded- collect in pile- anode sludge

55
Q

membrane cell requirements

A

for electrolysis of brine
- supply of electricity
- inert electrodes
- purified, concentrated brine
- only water supplied to cathode side
- positive ion permeable membrane separate anode and cathode compartments- only allow movement of Na+ cations

physics (33 decks)

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