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Electrochemistry Flashcards

1
Q

What is electrochemistry?

A

the study of chemical processes that cause electrons to move

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2
Q

How can a simple electrochemical cell be created?

A

two different metals dipped in salt solutions of their own ions joined by a salt bridge, connected to an external circuit

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3
Q

What are the two reactions that always occur in electrochemical cells?

A

oxidation and reduction

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4
Q

What does each beaker contain?

A

a half cell made up of a redox couple

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5
Q

What is a redox couple?

A

metal ions in equilibrium with its aqueous solution of ions

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6
Q

What is the salt bridge soaked in?

A

a strip of filter paper soaked in a solution of soluble ionic compound

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7
Q

What is the cell potential?

A

the voltmeter reading of potential difference between the two half-cells

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8
Q

What is the e.m.f (electromotive force)?

A

the cell potential under zero current conditions

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9
Q

Which direction do electrons flow?

A

from the more reactive metal to the less reactive metal

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10
Q

What does a positive voltmeter reading mean?

A

electrons flow left to right

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11
Q

What happens to the most reactive metal?

A

it gets oxidised and is the more negative electrode

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12
Q

How do you get the overall reaction?

A

by combining the two half equations

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13
Q

What is the electrochemical series?

A

a list of standard electrode potentials placed in order according to the value of the reduction process

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14
Q

Describe the layout of the electrochemical series

A

-most positive at the top (most strongly oxidising is positive, good at gaining electrons)
-most negative at the bottom (most strongly reducing is negative, worse at gaining electrons)

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15
Q

What is the formula for the oxidising agent accepting electrons?

A

ox + e- ⇌ red NEED STATE SYMBOLS

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16
Q

The E value of a redox couple gives a…

A

quantitative measure of equilibrium

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17
Q

What happens to the equilibrium if the E value is positive?

A

the more likely the forward reaction is to occur, correspond to reduction

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18
Q

What happens to the equilibrium if the E value is negative?

A

the more like the backward reaction is to occur, correspond to oxidation

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19
Q

Any species on the left hand side can oxidise…

A

any species on the right-hand side below it

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20
Q

Any species on the right hand side can reduce…

A

any species on the left-hand side above it

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21
Q

What are good reducing agents?

A

reactive metals

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22
Q

What are three types of groups of electrochemical cells?

A

-primary cells
-secondary cells
-fuel cells

23
Q

What is a primary cell?

A

a primary cell is irreversible and non-rechargeable

24
Q

What is a secondary cell?

A

a secondary cell is reversible and is rechargeable

25
What is a fuel cell?
a fuel cell generates electricity from the continuous oxidation of an external source of fuel
26
What is the function of a primary fuel cell?
to provide current to an external circuit while discharging (galvanic action)
27
What is a galvanic cell?
a galvanic cell is one with a positive e.m.f in which the spontaneous forward cell reaction can be used to provide electric current to an external circuit
28
How do secondary cells work?
they combine two opposing functions of all reversible electrical cells - -they provide current to an external circuit while discharging (galvanic action) chemical into electrical energy -they use current from an external circuit while charging (electrolytic action) electrical into chemical energy
29
In order for the system to be truly reversible, what is important about the products?
that the products resulting from both galvanic and electrolytic action are not dispersed in the cell but remain attached to the cell electrodes
30
What is the equation to find Ecell?
Eright - Eleft right is the most positive, left is the most negative
31
Describe the lithium rechargeable cell
-one electrode is LiCoO2 -one electrode is graphite -electrolyte is a lithium salt in an organic solvent
32
What are the equations for the lithium rechargeable cell?
positive electrode/reduction : Li+(aq) + CoO2(s) + e- --> Li+[CoO2]-(s) negative electrode/oxidation : Li(s) --> Li+(aq) + e- OVERALL : Li(s) + CoO2(s) --> Li+[CoO2]-(s)
33
What is a benefit of lithium?
very light
34
What are fuel cells?
use a supply of hydrogen or organic fuel with a supply of oxygen to provide a source of electrical power
35
Why are fuel cells reliable?
there are no moving parts
36
What is the difference between batteries and fuel cells?
fuel cells consume reactants that must be replenished, whereas batteries store and release energy is a closed system
37
Describe the structure of a hydrogen-oxygen fuel cell
-hydrogen as a fuel on the anode side, oxygen as an oxidant on the cathode side -platinum-group metal/alloy as the catalyst
38
What are two properties of the platinum electrodes?
inert and porous - allows the passage of reactant and product gases
39
What can the electrolytes be in hydrogen-oxygen fuel cells?
-acidic - phosphoric acid -alkaline - hot aqueous potassium oxide
40
How do acidic hydrogen-oxygen fuel cells work?
-hydrogen diffuses to the anode platinum catalyst where it splits up to make H+ ions and electrons -hydrogen ions are conducted through the electrolyte to the cathode -the electrons travel through the external circuit -at the cathode platinum catalyst surface, oxygen molecules react with electrons and hydrogen ions to form water -water is the only waste product
41
How do alkaline hydrogen-oxygen fuel cells work?
-at the anode, hydrogen reacts with hydroxide ions, water and electrons are produced -electrons enter the external circuit -at the cathode, oxygen reacts with electrons arriving from the external circuit to make hydroxide ions
42
In acidic conditions, what are the electrode reactions?
overall : 2H2(g) + O2(g) --> 2H2O(l) oxidation : H2(g) --> 2H+(aq) + 2e- reduction : O2(g) + 4H+ (aq) + 4e- --> 2H20(l)
43
In alkaline conditions, what are the electrode reactions?
overall : 2H2(g) + O2(g) --> 2H2O(l) oxidation : H2(g) + 2OH-(aq) --> 2H2O(l) + 2e- reduction : O2(g) + 2H2O(l) + 4e- --> 4OH-(aq)
44
Why is the e.m.f exactly the same for both acidic and alkaline reactions?
they have exactly the same overall reaction
45
What is the cell representation for the acidic hydrogen-oxygen fuel cell?
Pt(s)│H2(g)│H+(aq)║O2(g)│H+(aq),H2O(g)│Pt(s)
46
What is the cell representation for the alkaline hydrogen-oxygen fuel cell?
Pt(s)│H2(g)│OH- (aq),H2O(l)║O2(g)│H2O(l),OH-(aq)│Pt(s)
47
Why do hydrogen-oxygen fuel cells only work under standard conditions limitedly?
-rate of flow of electrons is slow -usual to operate cell around 200C -however since the reaction is highly exothermic, increasing temp decreases e.m.f -therefore an increased pressure is used to compensate
48
How do we obtain hydrogen?
-oxygen can be cheaply obtained from the air -most hydrogen is produced by the reaction between methane and steam -high input of energy with a large carbon footprint
49
What is the overall reaction for the production of cycle from methane and steam?
CH4(g) + 2H2O(g) -- > CO2(g) + 4H2(g)
50
Are hydrogen-oxygen fuel cells really green?
water is the only product, but the hydrogen that is produced needs to be made cleanly, by the electrolysis of acidified water -the energy for this electrolysis must come from carbon neutral sources such as solar power
51
What is the overall equation for an organic fuel cell?
C2H6O + 3O2 --> 2CO2 + 3H2O
52
What is the SHE?
standard hydrogen electrode - measuring standard for half-cell potentials
53
What are the conditions of a cell potential 0.00V for a SHE?
-solutions are 1.0 moldm-3 conc -temp of 298K -100kPa pressure
54
What does a SHE consist of?
hydrochloric acid, hydrogen gas, platinum electrodes

Physical Chemistry (27 decks)

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