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General Chemistry MCAT > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Moles of electrons transferred during reduction

A
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2
Q

Electrodeposition equation

A
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3
Q

Standard electromotive force of a cell

A
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4
Q

Standard change in free energy from standard emf

A
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5
Q

Nerst equation

A
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6
Q

Nernst equation simplified

A
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7
Q

Reaction quotient

A
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8
Q

Standard change in free energy from equilibrium constant

A
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9
Q

Free energy change (nonstandard condition)

A
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10
Q

Electrochemical cell
(Types)

A

Describes any cell in which oxidation-reduction reactions take place.

1) Electrolytic cell
2) Galvanic (voltaic) cell
3) Concentration cell

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11
Q

spontaneous reactions in

A

galvanic cells and concentrations cells

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12
Q

nonspontaneous reactions

A

electrolytic cells

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13
Q

electrode where oxidation occurs

A

anode

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14
Q

electrode where reduction occurs

A

cathode

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15
Q

Electrodes in an electrochemical cell mnemonic

A

AN OX - anode oxidation
RED CAT - reduction cathode

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16
Q

emf positive

A

cell able to release energy G<0 so spontaneous

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17
Q

emf negative

A

cell must absorb energy, G>0 so nonspontaneous

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18
Q

electrons move from

A

anode to cathode

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19
Q

current runs

A

cathode to anode

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20
Q

Electrochemical cells
(Shared characteristics)

A

1) Electrodes are strips of metal or other conductive material placed in an electrolyte solution.

2) Anode is always the site of oxidation. It attracts anions.

3) Cathode is always the site of reduction. It attracts cations

4) Electrons flow from anode to cathode.

5) Current flows from cathode to anode.

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21
Q

In electrochemical cell, electrons flow

A

A -> C
anode to cathode

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22
Q

The purpose of the salt bridge

A

is to exchange anions and cations, to balance, or dissipate, newly generated charges

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23
Q

Cell diagrams

A

Shorthand notation that represents the reactions taking place in a cell.

1) Written from anode to cathode with electrolytes (the solution) in between.

2) A vertical line represents the phase boundary, and a double vertical line represents a salt bridge or other physical barrier.

anode | anode sol’n (conc) || cathode col’n (conc) | cathode

24
Q

Ecell positive

A

free energy change is negative so spontaneous

25
Q

Galvanic (voltaic) cells

A

House non rechargeable batteries, spontaneous reactions (G<0) with a positive electromotive force.

26
Q

Electrolytic cells

A

House non spontaneous reactions (G>0) with a negative electromotive force. These non spontaneous cells can be used to create useful products through electrolysis.

27
Q

Concentration cells

A

Specialized form of a galvanic cell in which both electrodes are made of the same material. Rather than a potential difference causing the movement of charge, it is the concentration gradient between the two solutions.

28
Q

Daniell cell

A

in this galvanic cell, zinc is the anode and copper is the cathode
each electrode is bathed in an electrolyte solution containing its cation and sulfate
contains slat bridge
copper precipitates onto the electrode (process called plating/galvanization)

CuSO4
NuSO4

29
Q

purpose of salt bridge

A

exchange anions and cations to balance, or dissipate, newly generated charges

30
Q

Charge on the electrode?

A

Dependent of the type of electrochemical cell being studied:

1) Galvanic cells, the anode is negatively charged and the cathode is positively charged.

2) Electrolytic cells, the anode is positively charged and the cathode is negatively charged.

No matter what anions are attracted to the anode and cations are attracted to the cathode

31
Q

Rechargeable batteries

A

Electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states.

Rechargeable batteries are often ranked by energy density – the amount of energy a cell can produce relative to the mass of the battery material.

32
Q

Lead-acid batteries

A

When discharging, consist of a Pb anode and a PbO2 cathode in a concentrated solution of sulfuric acid.

When charging, PbSO4- plated electrodes are dissociated to restore the original Pb and PbO2 electrodes and concentrate the electrolyte.

33
Q

Nickel-cadmium batteries

A

When discharging, consist of a Cd anode and a NiO(OH) cathode in a concentrated solution of KOH.

When charging, the Ni(OH)2- and Cd(OH)2- plated electrodes dissociate to the original Cd and NiO(OH) electrodes and concentrate the electrolyte. The cells have a higher density than lead-acid batteries.

34
Q

nickel-metal hydride batteries

A

replace Ni-Cd batteries, more energy dense, more cost effective, significantly less toxic

35
Q

Surge-current

A

An above average current transiently released at the beginning of the discharge phase, it wanes rapidly until a stable current is achieved.

36
Q

Reduction potenial

A

reduction potential, the more a given species wants to be reduced.

I.E. O2 = highest @ 1.4

37
Q

Standard reduction potential (Ered)

A

Calculated by comparison to the standard hydrogen electrode (SHE) under standard conditions (298K, 1M, 1ATM).

38
Q

SHE (reduction potential)

A

Standard hydrogen electrode reduction potential = 0V

39
Q

Standard electromotive force

A

The difference in standard reduction potential between the two half-cells.

40
Q

Galvanic cells vs Electrolytic cells (Ered)

A

Galvanic cells- the reduction potential between the two half-reactions is positive.

Electrolytic cell- the reduction potential between the two half-reactions is negative.

41
Q

Electromotive force and change in free energy
(Trends)

A

When Ecell = +, ΔG = - (galvanic cells).

When Ecell= -, ΔG = + (Electrolytic cells)

When Ecell = 0, ΔG = 0. (concentration cells)

42
Q

Nernst equation

A

Describes the relationship between the concentration of species in a solution under nonstandard conditions and the electromotive force.

43
Q

Relationship between Keq and Ecell

A
44
Q

anode of electrolytic cell

A

positive because attached to positive pole of external voltage source and attracts anions

45
Q

cathode of electrolytic cell

A

negative because it is attached to the negative pole of the external voltage source and attracts cations from solution

46
Q

anions are ALWAYS attractive to the

A

anode and cations to the cathode, true regardless of the type of cell

47
Q

More positive Ered

A

greater relative tendency for reduction to occur, while a less positive mean greater relative tendency for oxidation to occur

48
Q

for galvanic cells, the electrode with the more positive reduction potential is the

A

cathode

49
Q

for electrolytic cells, the electrode with more positive reduction potential is forced by the external voltage source to be oxidized and therefore the

A

anode

50
Q

if you need to multiply each half-reaction by a common denominator to cancel out electrons when coming up with the net ionic equation,

A

do not multiply Ered by that number, that would indicate a change in the chemical identity of the electrode which is not occurring

51
Q

for redox reactions with the equilibrium constants less than 1,

A

Ecell is negative and therefore electrolytic

52
Q

for reactions with keq greater than 1

A

Ecell is positive and therefore galvanic

53
Q

Electrodes

A

strips of metal or other conductive materials placed in an electrolyte solution

54
Q

Anode

A

is always the positive site for oxidation. It attracts anions

55
Q

Cathode

A

is always the site of reduction. It attracts cations

General Chemistry MCAT (12 decks)

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