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chemistry 1102 > Chapter 17: Electrochemistry > Flashcards

Chapter 17: Electrochemistry Flashcards

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1
Q

what is electrochemistry

A

a branch of chemistry that relates electricity and chemical reactions

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2
Q

what does the law of conservation of mass say

A

amount of each element must be the same on both sides

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3
Q

what can be used to balance the gains and losses of electrons

A

half reaction metod

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4
Q

what is oxidation

A

lose electrons (more positive)

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5
Q

what is reduction

A

gain electrons ( more negative)

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6
Q

what is the half reaction method

A
  • write the oxidation and reduction as two separate processes
  • balance the 1/2 reactions then combine them to attain the balanced equation for the overall reaction
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7
Q

if there is oxidation in a reaction where are the electrons

A

on the right (products)

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8
Q

if there is reduction where are the electrons in the rxn

A

electrons are on the left (reactants)

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9
Q

if a reaction occurs in a basic solution how do you balance it

A

balance it as if it occurred in an acid

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10
Q

what happens to the electrons in a spontaneous redox rsn

A

electrons are transferred and energy is released

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11
Q

why are redox reactions in energy

A

have the potential to generate electrical current
- use the energy to make the electrons go through an external device

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12
Q

what is another name for the voltaic cell

A

galvanic

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13
Q

in a voltaic cell, setup do the metals touch

A

the metals are not direct

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14
Q

why do we separate the reduction and oxidation half reactions

A

so that we can create a flow of electrons

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15
Q

what is the purpose of an electrode

A

electron flow though a wire with ion flow through a solution

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16
Q

what does electrode require

A

conductive solid electrode

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17
Q

what is an electrode

A

two solid metals connected by external circut

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18
Q

where does oxidation occur in a voltaic cell

A

anode

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19
Q

where does reduction occur in a voltaic cell

A

cathode

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20
Q

in the cell how do the electrons flow

A

leave the anode and flow through the wire to the cathode

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21
Q

what happens when the electrons leave the anode

A

cations formed dissolve into the solution in the anode compartment
- anode loses mass and the soln becomes more concentrated

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22
Q

what happens when electrons reach the cathode

A

cations in the solution the cathode is in are attracted to the now negative cathode

  • cathode gains mass and the soln it is in becomes less concentrated
  • electrons form neutral metals
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23
Q

what is a salt bridge

A

u shaped tube that contains a salt solution, to keep the charges balanced

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24
Q

what is the salt bridge composed of

A

ions that will not react with other ions in the cell or with the electrode materials

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25
Q

why do we use an electrolyte in thecell

A

to keep it from pouring out into the two half cells

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26
Q

what sign is the anode labled with

A

negative

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27
Q

what sign is the cathode labeled with

A

+

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28
Q

what is the formula for cell notation

A

electrode | electrolyte || electrolyte | electrode

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29
Q

in cell notation what is on the left

A

oxidation half cell

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30
Q

in cell notation what is on the right

A

reduction half cell on the right

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31
Q

what does || mean in cell notation

A

salt bridge

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32
Q

what does | mean in cell notation

A
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33
Q

what do you use when mulltiple electrolytes are in the same phase

A

, (comma)

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34
Q

what is potential difference

A

the difference in potential energy per electrical charge between two electrodes

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35
Q

what is a potential difference measured in

A

Volts

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36
Q

what is the coulomb the derived SI unit for

A

electrical charge

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37
Q

what does 1 volt equal

A

1 v = 1 J/C
- C = 1A x 1S

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38
Q

what is the charge of one electron

A

1.60 x 10^-19 C

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39
Q

what is the electromotive force

A

potential diff. between the anode and cathode

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40
Q

what does electromotive mean

A

causing electron motion

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41
Q

what is another name for emf (electromotive force)

A

cell potential

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42
Q

how does a voltmeter work

A

by drawing current through a known resistance

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43
Q

what happens in the voltmeter

A
  • current flows through wire generating frictional heat and wastes some energy
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44
Q

what happens in a digital voltmeter

A

draw only a negligible current and are physically and financially convenient

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45
Q

what will happen to the cell potential it it is +

A

cell rxn proceeds spontaneously

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46
Q

Ecell is referred to and measured in what

A

cell voltage and measured in volts

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47
Q

what does the emf depend on

A

the particular cathode and anode

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48
Q

what is the name for cell potential under standard conditions

A

standard emf

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49
Q

what is cell potential

A

difference between the two electrode potentials

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50
Q

electrode potentials at standard conditons are for what

A

reduction reactions

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51
Q

why is it impossible to measure the standard reduction potential of a half reaction directly

A

the voltaic cell involves two half cells

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52
Q

what is SHE

A

standard hydrogen electrode

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53
Q

what is the SHE

A

the reduction of H+ to H2 under standard conditions

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54
Q

what is the reduction potential for hydrogen

A

0 V

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55
Q

what does a SHE consist of

A

electrode with finelt divided pt (platinum) in contact with H2(g)

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56
Q

what happens when SHE is the cathode

A

two H+ ions each accept an electron from the pt electrode and are reduced to H atoms

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57
Q

when SHE is the anode what happens

A

H2 molecule at the electrode surface loses two e-s and is oxidized to H+

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58
Q

what is cell potential based on

A

the potential energy per unit of charge (intensive property)

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59
Q

what happens if we increase the amount of substances in a redoz reaction

A

increaese the energy and charges but the ratio of energy to charge would remain constant

60
Q

what does the Ered measures

A

the driving force for red to occur

61
Q

what happens if the Ered is more positive

A

the greater the driving force

62
Q

in a voltaic cell what has a more positive value for Ered

A

the cathode

63
Q

what is the greater force of the cathode used for

A

used to force the anode rxn to occur in reverse

64
Q

what is the equation for the Ecell

A

Ecell  = Ered (cathode) + (−Ered (anode)

65
Q

what is another name for the standard cell potential

A

Ecell

66
Q

what are the strongest oxidizers and what does it mean if they are the strongest

A

the one with the most Ered, they have a greater tendency for the reactant of the half rxn to be reduced and oxidize another species

67
Q

the strongest reducers have the most

A

negative Ered

68
Q

what is the half rxn with the smallest ered

A

reversed as an oxidation

69
Q

how do you find E standard

A

E = Ered (reduction) − Ered   (oxidation

70
Q

what does a positive E indicate

A

a spontaneous process

71
Q

when is 1 Joule of work produced

A

when 1 coulomb of charge is transferred between points

72
Q

what is the equation for cell potential and electrical work

A

emf = potential difference = E = 1V = work(J)/ charge (c)

73
Q

what is the equation for energy involving work

A

-w/q

74
Q

what is the equation for q that involves F

A

q = nF

n = moles of electrons

-F = faraday’s constant (96,485 C/mol e-)

75
Q

what is the equation for max work in a cell

A

wmax = −qEmax

76
Q

how do you find change in free energy with max work

A

∆G = wmax = −qEmax = −nFE

77
Q

for a spontaneous rxn at standard conditions

what is the sign of G, K, and E

A

G = -

K = +

E = +

78
Q

what happens when a voltaic cell is discharged

A

the reactants are consumed and the products are produced

  • concentrations of reactans and products are not constant they change over time
79
Q

what will E reach when the emf decreases

A

0

80
Q

what can we use to calulate the emf under nonstandard conditions

A

nernst equation

81
Q

who came up with the nernst equation

A

walther nernst

82
Q

what is the nernst equation

A

= E − RT nF ln Q = E − 2.303 RT nF log Q

83
Q

what is the nernst equation for room temperature

A

E = E − 0.0592 V/ n log Q

84
Q

what is the nernst equation when Q = K

A

E = 0.0592 V n log K

85
Q

what is a conc. cell

A

a cell based on the emf generated because of a difference in concentration

86
Q

where do electrons flow when the cell concentrations are different

A

electrons flow from the side with less conc soln (anode) to the side with more conc( cathose)

87
Q

what will happen if there is oxidation of the electrode in the less conc.

A

soln will increase the ion conc in the soln

88
Q
A
89
Q

what does the reduction of the soln in the more concentration do to the ion concentration of the soln

A

it reduces the ion conc

90
Q

what is cell potential sensitive to

A

concentrations of reactans and products

91
Q

what can you use measured potentials for

A

used to determine the concentration of an ion

92
Q

what does a pH meter do

A

measures the conc using an observed potential and consists of three main componenets

93
Q

what are the 3 main components of a pH meter

A
  1. ) standard electrode of known potential (typical Ag/AgCl)
  2. ) special glass electrode that changes potential
  3. ) potentiometer that measures the potential btwn electrodes
94
Q

what solution is in the glass electrode of a pH meter

A

HCL

95
Q

what does the electrical potential depend on in a pH meter

A

difference in protons btwn the reference soln and the soln the electrode is in

  • potential varies with the pH of the soln tested
96
Q

what is the potentiometer between electrodes converted into

A

a direct reading of pH

97
Q

what are ion-selective electrodes

A

electrodes that are sensitive to the concentration of a particular ion

example: glass electrode for pH meter

98
Q
A
99
Q

how can you make an electrode sensitive to other ions

A

by changing the composition of the glass

100
Q

what ions can be detected by replacing the glass membrane with an appropriate crystal

A

F-, Ag+, S-2

101
Q

what is a battery

A

portable self contained electrochemical power source that has 1 or more voltaic cells

102
Q

how can you achieve greater voltages from a battery

A
  • using multiple voltaic cells
  • using multiple batteries in a series
103
Q

how are the cells connected in a battery?

how are the cathode and anode connected?

A

they are connected in a series

  • cathode of one cell is connected to the anode of another
104
Q

what is the total voltage

A
105
Q

what sign is used to represent a cathode

A

+

106
Q

what sign is used to represent an anode

A

-

107
Q

what does the lifetime of a battery depend on?

A

the quantities of the substances that are oxidized and rediced

108
Q

what are the two main types of batteries

A

primary and secondary cell batteries

109
Q

what are primary cell batteries

A

cannot be recharged; discarded when emf drops to zero

110
Q

what is a secondary battery

A

can be recharged from an external power source after its emf drops

111
Q

what is the composition of a lead batter

A

automotive battery that consists of 6 cells in a series

-

112
Q

what is the anode in a lead battery

A

Pb

113
Q

what is the cathode in a lead battery

A

PbO2

114
Q

what is the cell voltage in a lead battery

A

12 V

115
Q

what is recharging and what does it generate

A

an external source of energy is used to reverse the overall cell reaction

  • generates Pb and PbO2
116
Q

what does the alternator do

A

provides the energy needed to recharge

117
Q

what is an alkaline battery

A

most common primary (non-rechargeable) battery

118
Q

what is the anode in an alkaline battery

A

Zn or Mg

119
Q

what is the cathode in an alkaline battery

A

MnO2 and graphite

120
Q

what is the eleectrolyte in an alkaline battery

A

KOH

121
Q

what is an alkaline battery separated by

A

porous fabric

122
Q

what is the cell voltage of an alkaline battery

A

1.55 V @ 25 degrees

123
Q

what is the nickel-cadium battery and what is it used in

A

most rechargeable battery

  • used in cell phones, laptops, video cameras
124
Q

what is the anode and cathode for nickel cadium batter

A
  • anode = cadmium metal
  • cathode = nickel oxyhyrdoxide
125
Q
A
126
Q

what is the electrolyte and cell voltage of nickel-cadium battery

A
  • electrolyte: KOH
  • cell voltage = 1.30 V
127
Q

what are the pros and cons of a nickel cadium batter

A
  • pros: rechargeable, long life, and lightweight
  • cons: Cd is toxic
128
Q

what is the difference between metal hydride battery compared to NiCad

A
  • an improvement to NiCad batteries
  • cathode is the same anode is different
129
Q

what is anode for NiMH battery

A

metal alloy with dissolved hydrogen

130
Q

what is the electrolyte and cell voltage for a NIMH battery

A

electrolyte = KOH

cell voltage = 1.30 v

131
Q

what is the lithium ion battery

A

newest rechargeable battery

132
Q

what is the Li-ion battery used in

A

cell phones and laptops

133
Q

what is the anode and cathode of the Li-ion battery

A

anode = graphite

cathode = lithium cobalt oxide

134
Q

what is Li-ion electrolyte and cell voltage

A
  • electrolyte = KOH

cell voltage = 3.7 V

135
Q

what are the pros of the li-ion battery

A

rechargeable, long life, very light more environmentally friendly

136
Q

what can the thermal energy released by combustion turn into

A

electrical energy

137
Q

what are fuel cells

A

the direct production of electricity from fuels by a voltaic cell yields a higher conversion rate

138
Q

what does PEM stand for

A

proton exchange membrane

139
Q

what is corrosion

A

the spontaneous oxidation of metals by chemicals in the environment

140
Q

what does the rusting of iron require

A

oxygen and water

141
Q

what is an electrolysis reaction

A
  • forces a current through a cell to produce a chemical change for which the cell potential is negative
142
Q

what are the practical purposes

A

the charging a battery producing aluminum, purifying metals, and electroplating

143
Q

where does electrolysis take place

A

electrolytic cells

  • requires an external power source to supply greater energy than EMF
144
Q

what is the 3rd most abundant element on earth and where is found

A

aluminum, found in nature as an oxide

145
Q

impure metals can be purified by what

A

electrolysis

146
Q

what is electroplating

A

uses electrolysis to deposit a thin layer of one metal on another metal

chemistry 1102 (6 decks)

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