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Chemistry > Chapter 10 - Electrochemical Cells > Flashcards

Chapter 10 - Electrochemical Cells Flashcards

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1
Q

in a redox reaction, to what substance and from what substance are electrons transferred?

A

transferred from substance that’s oxidized to substance that’s reduced

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2
Q

energy involved in a redox reaction and what form it is in?

A

releases small quantity of thermal energy

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3
Q

how do you harness the energy in a redox reaction and why?

A

separate oxidizing agent from reducing agent in a way that forces electron transfer through a wire, when the electrons flow through a wire, an electric current is produced so thermal energy is not released into environment and we can harness it

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4
Q

define half-cell

A

an electrode and electrolyte that form half of a complete cell

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5
Q

what is the electrolyte in the half-cell

A

solution of ions

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6
Q

define electrode

A

a solid electrical conductor

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7
Q

define cell

A

a system in which two connected electrodes are in contact with an electrolyte

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8
Q

how is a current produced using the galvanic cell

A

ions on the right in the solution will attract electrons from the electrode on the left, resulting in a flow of current from the electrode to the ions in the solution

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9
Q

what happens to the current in a galvanic cell that causes a problem?

A

current flows for an instant and stops

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10
Q

why does the current stop after an instant in a galvanic cell with the left cell?

A

oxidation of electrode on left results in an increase in concentration of ions in that half-cell, resulting in a build-up of positive charge

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11
Q

why does the current stop after an instant in a galvanic cell with the right cell?

A

reduction of ions in the solution on the right reduces concentration of ions on the right, resulting in a build up of negative charge due to the other different ions that remain

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12
Q

why does the current stop after an instant in a galvanic cell in general

A

charges build up in both half-cells preventing electron transfer from occurring

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13
Q

how is the problem of current stopping in a galvanic cell fixed?

A

connecting the solutions so ions can flow between them to keep the net charge in each half-cell at 0

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14
Q

define salt bridge

A

a tube that contains a non-reactive electrolyte solution and connects the two half-cells in a galvanic cell

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15
Q

why do we plug the ends of the salt bridge with cotton plugs?

A

to prevent solution from falling out of tube but they are porous enough to permit some fluid and ions to flow in and out of the tube

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16
Q

when looking for a non-reactive electrolyte for the galvanic cell, what do we look for?

A

one that is soluble and won’t react with electrodes or the electrolyte solutions

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17
Q

what happens to the non-reactive electrolyte in the salt bridge as it progresses, if we use sodium sulfate

A

negatively charged sulfate ions (SO4^2-) spontaneously migrate to the left half-cell to offset build up of ions, positively charged sodium ions (Na+) spontaneously migrate into right half-cell to offset loss of ions, so the solutions in both remain electrically neutral

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18
Q

define galvanic cell

A

an arrangement of two connected half-cells that spontaneously produces electric current

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19
Q

define anode and what side of the galvanic cell is it on?

A

electrode where oxidation occurs, left side

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20
Q

define cathode and what side of the galvanic cell is it on?

A

the electrode where reduction occurs, right side

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21
Q

explain how a galvanic cell works with anodes and cathodes

A

electrons flow spontaneously from the anode to the cathode from an external path (the conducting wire), in the salt bridge, anions (negatively charged ions) flow to the anode and cations (positively charged ions) flow to the cathode

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22
Q

why is the zinc electrode on the left decreasing in mass in the galvanic cell?

A

oxidation of the zinc metal is occurring at the zinc anode Zn (s) - Zn^2+ (aq) + 2e-

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23
Q

mass of copper electrode in galvanic cell?

A

increases

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24
Q

why does the copper electrode increase in mass in galvanic cell and what does this cause?

A

copper is deposited on it, blue colour of the solution decreases in intensity, copper (ii) ions in solution are reduced to copper metal at the copper cathode Cu^2+ (aq) + 2e- - Cu(s)

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25
charges of each electrode in the galvanic cell
zinc on left has negative charge and copper on right has positive charge
26
why does the zinc electrode have a negative charge and the copper electrode has a positive charge?
electrons move from zinc electrode to copper electrode
27
why do the electrons flow to the copper ions rather than the zinc ions?
they both act as oxidizing agents and are capable of accepting electrons, copper is a stronger oxidizing agent than zinc
28
difference between metal electrode vs battery
metal electrode and metal ions, metal electrode participates in the cell reaction. in a battery, carbon (graphite) is often used as an electrode as an inert solid conductor
29
how are inert electrodes useful?
provides a surface on which the oxidation and reduction reactions can occur, but it does not participate, reaction involves entities in the solution, not the electrode; acts as inert solid conductor, a place to connect the wire
30
where do reactions take place in galvanic cells
in aqueous solutions
31
what is line notation
an abbreviated way to describe cells
32
explain how to write line notation
anode components listed on left, cathode components on right, separated by double vertical lines to indicate salt bridge, single vertical line indicates boundary between 2 states of matter
33
when writing line notation, where is the positive charge ions and negative charged ions and what is at the ends
positive electrolyte on left as aqueous, negative electroyte on right as aqueous, solid inert electrode used at the ends, anode on the left, cathode on right
34
2 connections required before a galvanic cell can function
wire connects two electrodes and salt bridge to connect 2 solutions
35
where do you draw elements in galvanic cell?
reduction/oxidation agent solid on electrode, reduction/oxidation agent ion and other ion in solution, two ions going from the salt bridge
36
where do you draw electron/ion flow in galvanic cell
on left, going up into wire and solution from electrode, going from ion into salt bridge, from salt bridge to other ion, on right - from wire into electrode, from ion to electrode, from other ion into salt bridge
37
energy converted from what to what in a galvanic cell?
chemical energy from spontaneous redox reaction to electrical energy
38
define cell potential, SI unit, unit symbol
the electric potential difference (voltage) between the 2 half-cells in a galvanic cell; SI unit is volt, unit symbol is V
39
volt to J/C
1 to 1
40
cell potential ratio
joule of energy per coulomb of electric charge
41
what does not affect cell potential
number of electrons transferred as a galvanic cell operates
42
give an example of battery with what does not affect cell potential
D cells transfer electrons for a longer time than AAA cells because it contains more reactants, but the quantity of energy per charge transferred is identical
43
what are factors that influence cell potential
design of cell, redox reaction involved, concentration of reactants in the cell
44
what does a voltmeter measure?
cell potential
45
what does a negative reading on a voltmeter indicate?
connections are reversed, positive terminal should be connected to cathode, negative terminal should be connected to anode
46
define standard cell
a galvanic cell in which all the entities involved in the half-cell reaction are at SATP and the solutions have a concentration of 1.0 mol/L
47
define standard cell potential
the electric potential difference of a galvanic cell that is operating under standard conditions, potential energy difference, per unit of charge, between cathode and anode
48
what does the degree symbol mean
standard conditions
49
symbol for standard cell potential
ΔE°r(cell)
50
define standard reduction potential
the ability of a half-cell to attract electrons in a cell that Is operating under standard conditions
51
how do we come to the formula for standard cell potential
as a cell operates, the half-cell with the more positive reduction potential gains electrons from the half-cell with the lower reduction potential
52
what is the symbol for standard reduction potential
E°r
53
standard cell potential formula
ΔE°r(cell) = E°r (cathode) - E°r (anode)
54
why did we create the standard hydrogen half-cell
electric potential of a half-cell cannot be measured because a half-cell reaction cannot occur on its own
55
define standard hydrogen half-cell
the galvanic cell from which all the half-cell potentials are determined
56
by definition what is E°r
0 V
57
how do we develop a reduction potentials table
zinc ions are in the left half-cell, hydrogen ions in the other, due to their positive charge, both compete for electrons and can be oxidizing agents, but, positive cell potential indicates electrons flow from zinc anode to platinum cathode, since cell potential is 0.76 and therefore reduction potential of hydrogen ions is greater than zinc ions by 0.76 so reduction potential of zinc ions must be -0.76
58
what is value of standard cell potential if the reaction is spontaneous
greater than 0
59
magnitude of standard cell potential, what it doesn't indicate and what actually happens
does not indicate speed of reaction, as cell operates, observed potential decreases as chemicals are used up and they are not longer at standard conditions
60
value of standard cell potential if reaction is at equilibrium
0
61
what happens and must happen to cell when reaction reaches equilibrium
forward and reverse reactions are occurring at the same rate, reaction has reached chemical equilibrium, cell must be recharged
62
value of standard cell potential if reaction is a non-spontaneous reaction
below zero
63
how can a cell reaction be made to occur if it is non-spontaneous
applying energy from an external source
64
how are cells arranged in a series and what this forms
anode of one cell is connected to the cathode of the next cell, one end of the chain cell is an anode and the other end is a cathode, these ends form the terminals in the battery
65
define battery
a group of 2 or more galvanic cells connected in series
66
why do unused batteries still work after being stored for months?
electron flow only occurs when a device that draws electrical energy is attached to the terminals
67
electric potential difference/voltage of cells connected in a series
the sum of the cell potentials of the cells
68
why does a light bulb attached to a 9 v battery glows more brightly than if it were connected to a single cell
9 v transfers more electrical energy than of its cells individually
69
define primary cell
a cell that cannot be recharged
70
when does a primary cell stop providing electrical energy
when reactants are used up
71
define secondary cell
a cell that can be recharged by being attached to an external source of electrical energy; recharging reverses the chemical reaction that generates electrical energy (regenerates reactants)
72
where are alkaline dry cells used?
remote controllers, watches, flashlights
73
what kind of cell is an alkaline dry cell
primary
74
what an alkaline dry cell looks like
anode consists of paste of zinc metal, electrolyte paste is surrounded by a cathode of solid manganese dioxide, anode and cathode are separated by porous fabric - prevents chemicals from coming in direct contact while still allowing ion flow
75
explain chemical reaction of an alkaline dry cell
as cell generates electrical energy, electrons are released from oxidation, electrons flow through central collector and out of the cell via negative terminal and through device requiring electrical energy, electrons return via positive terminal where they take part in reduction half-reaction
76
anode-half reaction of alkaline dry cell (oxidation)
Zn(s) + 2 OH- (aq) - ZnO (s) + H20 (l) + 2e-
77
cathode half reaction of alkaline dry cell (reduction)
2 MnO2 (s) + h20 (l) + 2e- - Mn2o3 (s) + 2 oh- (aq)

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