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CH302 > Unit 4: Electrochemistry > Flashcards

Unit 4: Electrochemistry Flashcards

1
Q

Electrochemistry

A

the study of the movement of electrons from one chemical species to another in chemical reactions

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2
Q

Electrochemistry is the study of chemical reactions that ________ electricity and chemical reactions that can be carried out by _____________

A

give off, running electricity through them

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3
Q

Oxidation-reduction (redox) chemistry is the study of the movement of electrons from __________ in chemical reactions

A

one atom to another

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4
Q

All electrochemical reactions involve…

A

the transfer of electrons from one atom to another

Sometimes when the electron(s) are transferred a bond is formed between the two atoms, and sometimes the electrons are transferred with no bond forming between the atoms.

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5
Q

when assigning oxidation numbers we’re going to treat every compound as if it were an _______ compound even when we know it’s not. There are no ____________ when assigning oxidation numbers.

A

ionic, “shared electrons”

each electron belongs entirely to one atom or to another atom.

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6
Q

Any atom in a neutral element has an oxidation number of _______.

A

0

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7
Q

A neon atom (Ne) has an oxidation number of ________, and so do both atoms in an H2 molecule.

A

0

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8
Q

The oxidation state of any monatomic ion is equal to the _________ on the ion.

A

charge

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9
Q

Na+ and H+ both have an oxidation number of _________.

A

+1

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10
Q

In a neutral compound the oxidation numbers of all the atoms in the compound add up to _____

A

0

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11
Q

Each H atom in H2O is in a ___ oxidation state and the oxygen is __.

A

+1, –2
These add up to 0.

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12
Q

in a polyatomic ion the oxidation numbers of all the atoms in the polyatomic ion add up to the __________.

A

charge on the ion

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13
Q

In a hydroxide ion, OH–, the oxygen is in a __ oxidation state and the hydrogen is __.

A

–2, +1

adding up to the charge on the ion, 1–.

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14
Q

In compounds hydrogen almost always has an oxidation number of __

A

+1

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15
Q

In compounds oxygen almost always has an oxidation number of __.

A

-2

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16
Q

elements H2 and O2, the oxidation numbers are __.

A

0

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17
Q

When hydrogen appears at the end of a compound formula that _________, that hydrogen is in a __ oxidation state. This type of compound is called a ____________.

A

begins with a metal, –1, metal hydride

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18
Q

There are only two metal hydrides that you might see in this class:

A

Lithium aluminum hydride, LiAlH4, and sodium borohydride, NaBH4.

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19
Q

When oxygen is in a compound called a peroxide, the O atoms are both __.

A

–1

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20
Q

The most common peroxide and the only one you’ll see in this class is…

A

hydrogen peroxide, H2O2 (H-O-O-H)

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21
Q

Halogens are always __ in compounds unless they are bonded to _______, in which case their oxidation state will depend on how many ________ they are bonded to.

A

–1, oxygen, oxygens

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22
Q

in NaClO4 the oxidation number of the Cl atom is __.

A

+7

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23
Q

What is the oxidation number of the manganese in Mn3(PO4)2?

A

+2

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24
Q

Anytime you see a phosphate ion the phosphorus atom will be in a __ oxidation state.

A

+5
PO43-

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25
Q

Redox reactions

A

reactions in which atoms undergo a change in oxidation number by exchanging one or more electrons from one atom to another

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26
Q

If any atom’s oxidation state changes from the reaction side to the product side, that means it is ___________ during the reaction, and the reaction is a ____________.

A

gaining or losing electrons, redox reaction

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27
Q

Oxidation is the ____ of electrons

A

loss

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28
Q

Anything that loses electrons is said to be ________, and its oxidation number __________.

A

oxidized, increases (becomes more positive)

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29
Q

Reduction is the ____ of electrons.

A

gain

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30
Q

Anything that gains electrons is said to be _______, and its oxidation number ____________.

A

reduced, decreases (becomes more negative)

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31
Q

If something in a chemical reaction is oxidized, something else in the reaction must be ________.

A

reduced

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32
Q

Sn (s) + 2HCl (aq) ⟶ SnCl2 (aq) + H2 (g)

This _________ a redox reaction. __ is being oxidized and __ is being reduced.

A

is, Sn, H

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33
Q

The reactant that is providing the electrons is called the ___________.

A

reducing agent

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34
Q

The reactant that is taking the electrons away is called the ____________.

A

oxidizing agent

35
Q

LEO says GER

A

Lose Electrons Oxidation
Gain Electrons Reduction

36
Q

The activity series is a list of…

A

metal oxidation half-reactions
list that ranks metals by how easily they give up their electrons

37
Q

Higher up in the activity series means a metal is more…

A

easily oxidized in a chemical reaction
higher free energy
more reactive
strongest reducing agents (“want” to give up their electrons)

38
Q

Activity table:
When you draw a connecting line from the metal to the ion, if the line goes down that means the reaction _____________.

A

will be spontaneous
electrons experienced a negative ΔG, which means a spontaneous process.

39
Q

Activity table:
If when you connected the metal to the ion your line had to go up, that would be a ___________ reaction.

A

nonspontaneous

40
Q

Since each beaker contains half of the reactants and half of the products of the overall reaction, we say that each of the beakers is a ___________.

A

half-cell

41
Q

A chemical reaction that produces electricity would be

A

spontaneous

42
Q

The electrode where oxidation occurs (where the electrons are coming from) is called the _________.

A

anode

43
Q

The electrode where reduction occurs (where the electrons are headed) is called the __________.

A

cathode

44
Q

No matter how the cell diagram is drawn, in the shorthand notation the _________ always goes on the left and the _________ goes on the right.

A

anode, cathode

45
Q

Although it works exactly the same way as the activity series, the table of standard reduction potentials looks a little different. The half-reactions are written as _________ instead of as _________ as they were in the activity series, and the most easily oxidized species are at the ________ of the standard reduction potentials table instead of at the _________.

A

reductions, oxidations
bottom, top

46
Q

table of standard reduction potentials:
If your line goes down and to the right, that’s a _________reaction and it generates a _______________.

A

spontaneous, positive potential (positive voltage)

47
Q

If we’re talking about a cell potential under standard conditions, we call it __________

A

E° (“E-zero”)

48
Q

E° (“E-zero”) formula:

A

E°cell = E°reduction – E°oxidation

49
Q

If your calculated E°cell is positive, that means your cell __________. This kind of cell is called a ____________.

A

gives off electricity
galvanic cell or a voltaic cell

50
Q

If your calculated E°cell is negative, that means your reaction is __________. This kind of cell is called an ____________.

A

nonspontaneous
electrolytic cell
in order to make the reaction go in the forward direction you would have to put in electricity into it.

51
Q

oxidation always occurs at the ________ and reduction always occurs at the ________. A common mnemonic for this is __________________.

A

anode, cathode
ANode OXidation and REDuction CAThode

52
Q

in a galvanic cell the cathode is ________ and the anode is ________

A

positive, negative

53
Q

In an electrolytic cell the cathode is _________ and the anode is _________.

A

negative, positive

54
Q

In an galvanic cell, Ecell is () and ΔG is ().

A

+, –

55
Q

In an electrolytic cell, Ecell is () and ΔG is ()

A

-, +

56
Q

charge =

A

Current × time (in seconds)

57
Q

ΔG° = –(charge × ___________) = –(charge × __________)

A

voltage, E°cell

58
Q

C =

A

96485 C/mol × moles

59
Q

oxidation state of each atom?
I3-

A

-1/3

60
Q

ammonia

A

NH3

61
Q

ammonium

A

NH4+

62
Q

_________ reactions and __________ reactions are not redox reactions because electrons ___________

A

Acid-base, precipitation
do not move from one species to another in these reactions.

63
Q

primary batteries

A

Batteries that are not rechargeable

64
Q

secondary batteries

A

Batteries are rechargeable

65
Q

Steps for Balancing Redox Equations using the Half-Reaction Method

A
  1. Balance the main atom.
  2. Add H2O to balance oxygen.
  3. Add H+ to balance hydrogen. Add same # of OH- to both sides in basic solution and cancel out.
  4. Balance the charge using electrons.
66
Q

Without an external power supply to force the reaction to run in reverse (electrolytic cell), the ____________ reaction will occur.

A

spontaneous galvanic reaction

67
Q

If a reaction that is spontaneous under standard conditions is used to set up an electrochemical cell:

∆Gº will be __ 0
K will be __ 1
Eº will be __ 0

A

∆Gº will be < 0
K will be > 1
Eº will be > 0

68
Q

If a redox reaction that is non-spontaneous under standard conditions is used to set up an electrochemical cell:

∆Gº will be __ 0
K will be __ 1
Eº will be __ 0

A

∆Gº will be > 0
K will be < 1
Eº will be < 0

69
Q

Under standard conditions, an electrolytic cell has:

∆Gº will be __ 0
K will be __ 1
Eº will be __ 0

A

∆Gº will be > 0
K will be < 1
Eº will be < 0

70
Q

Under standard conditions, a galvanic cell has:

∆Gº will be __ 0
K will be __ 1
Eº will be __ 0

A

∆Gº will be < 0
K will be > 1
Eº will be > 0

71
Q

An electrochemical cell at equilibrium has:

∆Gº will be __ 0
K will be __ 1
Eº will be __ 0

A

∆Gº will be = 0
K will be :) 1
Eº will be = 0

The equilibrium constant doesn’t change when a reaction reaches equilibrium, so at equilibrium K is still equal to whatever it was before the reaction reached equilibrium.

72
Q

4Fe(s) + 3O2(g) –> 2Fe2O3(s)

What is the total number of electrons gained or lost by all iron atoms in the balanced equation?

A

loses 3 e-/Fe atom x 4 Fe atoms = loses 12 e-

73
Q

4Fe(s) + 3O2(g) –> 2Fe2O3(s)

What is the total number of electrons gained or lost by all oxygen atoms in the balanced equation?

A

gains 2 e-/O atom x 6 O atoms = gains 12 e-

74
Q

In a galvanic cell oxidation and reduction take place ___________, but at different __________

A

at the same time, electrodes

75
Q

In a working electrochemical cell (a galvanic cell or battery), the cations in the salt bridge move toward the ________.

A

cathode

76
Q

In an electrolytic cell, the negative terminal is the _________ and is the site of the ___________ half-reaction

A

cathode, reduction

77
Q

The electrons flow in the external circuit…

A

between the electrodes specifically

78
Q

If the table of standard reduction potentials is ordered with the strongest reducing agents at the top, how are the reduction potentials ordered (from top to bottom)?

A

from most negative to most positive

79
Q

Redox reactions are often _________ compared to other reactions such as acid-base reactions or precipitation reactions.

A

slow

80
Q

Nernst equation:

A

Ecell = Eºcell - (0.0591/n) log(Q)

81
Q

concentration cell
lower concentration =
higher concentration =

A

oxidation
reduction

82
Q

Faraday constant?

A

96,485 C/mol = the charge of one mole of electrons

83
Q

sulfide ion

A

S2-

84
Q

1 amp =

A

1 coulomb/second

CH302 (5 decks)

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