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book 2!! Flashcards

1
Q

what is an electrolyte

A

a substance that, when dissolved, gives a solution that conducts electricity

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2
Q

what type of substance are electrolytes

A

usually ionic substances

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3
Q

examples of electrolytes aka ionic substances

A

NaCl
KCl
Na2SO4

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4
Q

in an electrolyte solution,, how is current carried between electrodes

A

carried by the dissolved ions

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5
Q

what metal is used for electrodes

A

platinum

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6
Q

why is platinum used as the metal in a cell for electrodes

A

it’s inert
it’s unreactive

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7
Q

what is applied between the electrodes

A

voltage is applied
resistance is measured (R)

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8
Q

what is the resistance a measure of

A

it’s a measure of how difficult the motion of ions is between electrodes

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9
Q

what are the similarities and differences between the 2 electrodes

A

both platinum
same surface area
one positive (attracts negative ions)
one negative (attracts positive ions)

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10
Q

what does conductivity depend on

A

the conc
the higher the conc,, aka the higher the number of ions in solution,, aka more charge carriers available,, aka higher conductivity

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11
Q

strong electrolytes

A

fully ionise in solution
KCl
Na2SO4

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12
Q

when can ions behave independently in solution

A

when the solution is very dilute
when the ions are far apart

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13
Q

what’s an anion

A

negative ion

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14
Q

what’s a cation

A

positive ion

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15
Q

use of lithium instead of zinc does what to a battery

A

reduces its weight
gives a higher voltage (lithium is more reactive than zinc)

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16
Q

negative about alkaline and lithium batteries

A

they cannot be recharged.
their redox reactions aren’t reversible,, once the reaction has reached equilibrium,, it’s dead

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17
Q

how can batteries be recharged

A

by passing an electric current through them and so reversing the redox reaction

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18
Q

what does recharging a cell require

A

it requires the use of electricity to drive a chemical reaction in the non spontaneous direction

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19
Q

how is charge carried between the electrodes

A

by the dissolved ions from the electrolyte

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20
Q

what is an electrolyte

A

a substance that,, when dissolved,, gives a solution that conducts electricity

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21
Q

why is platinum used as an electrode

A

it’s inert

very unreactive

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22
Q

what is applied on the electrodes

A

voltage!!

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23
Q

what is measured when voltage is applied on the electrodes

A

the resistance is measured
R

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24
Q

what is resistance

A

a measure of how difficult the motion of ions is between electrodes

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25
positive ions move towards what
they move towards the negative electrode the anode
26
negative ions move towards the
the cathode
27
what happens at the anode
oxidation the negative electrode loses electrons to give to the positive ions
28
what happens at the cathode
reduction the cathode gains electrons from the negative ions
29
what does conductivity depend on
the number of ions in solution a higher concentration of ions = more charge carriers available,, higher conductivity
30
strong electrolytes areeee
fully ionised in solution
31
strong electrolytes + conductivity
dilute = higher conductivity due to interactions between ions affecting the movement of ions through the solution.
32
describe a daniel cell
Zinc in ZnSO4 LHS Copper in CuSO4 RHS 1 moldm-3 each
33
what is current
the flow of electrons between the half cells
34
what is a salt bridge used for
charge is conducted by ions in solution. current is carried by ions soaked in sodium sulfate keeps electrical neutrality flow of ions between cells
35
LHS is for the
anode oxidation occurs here Zn(s) -> Zn2+
36
RHS is for the
cathode reduction occurs here Cu2+ > Cu (s)
37
cell diagram steps
X (s) | X (aq) || Y (aq) | Y (s)
38
what is | in a cell diagram
phase boundary
39
what is || in a cell diagram
salt bridge
40
can we measure the potential of a single half cell
nope!! the volt meter shows the potential difference between the 2 half cells
41
what can we use to measure the potential of a single half cell
use a cell to compare the rest to!! use a standard hydrogen half cell
42
standard hydrogen half cell equation
2 H+ (aq) + 2e- —> H2 (g)
43
potential if a hydrogen half cell + what conditions it needs to be in
standard conditions: 1moldm-3, 1bar, 298k 0.00V
44
standard electrode potentials are actually
standard reduction potentials E* values
45
the more positive the E* (reduction potential) the…
stronger the oxidising agent (it helps other lose e- by taking them) the weaker the reducing agent (weaker bc it doesn’t help atoms gain electrons as it’s positive)
46
if the half cells E* value is more positive what does this mean
- oxidising agent - accepts electrons - reactions are written as reduction : the reaction is more likely to occur in the forward direction (the reduction direction)
47
what if the E* cell value is more negative
- reducing agent - loses electrons - more likely to occur in the reverse direction : bc reactions are written as reductions but it wants to lose electrons!!
48
the more positive reaction will do what do the more negative reaction
more positive,, wants to gain e- so it oxidises the more negative reaction
49
Br2 added to NaCl and NaI (both 1moldm-3) what happens
- write the reduction equation (electrochem series) - Br is added,, so we compare Br with I and Cl - Br is more negative than Cl- (it can’t oxidise it - take it’s electrons away) - Br is more positive than I- (it can oxidise it,, take its electrons away) bc I is more negative,, its half reaction will be an oxidation,, we reverse the electrochem reaction) then we combine the 2!! 💗💗
50
equation for finding the E* of the cell!!
E* cell = E* cathode - E* anode E* cell = E* reduction - E* oxidation
51
for the cell reaction to occur spontaneously,, what value must E*cell have
A POSITIVE VALUE!!!
52
what if the E* cell isn’t positive
the current reaction isn’t spontaneous it would occur spontaneously in the opposite direction to the cell diagram
53
what does the E*cell value tell us
tendency of the overall cell reaction to happen
54
what is an example of the electrochemical cell doing work
work = the movement of electrons around the circuit
55
cell doing work!!
movement of charge (electrons) around a circuit against resistance. required energy work done by the cell.
56
what does the energy required to transfer electrons//charge represent
the electrical work the cell can perform
57
what is z
moles of electrons
58
what is Q
total charge
59
what’s is F
faraday constant charge on 1 mole of electrons 96 485 coulombs
60
total charge produced equation
Q = zF Q= total charge z= moles F= faraday constant
61
Electrical work equation
-Q x V electrical work = -charge x potential difference
62
why is electrical work negative
bc it takes energy for it to occur the reaction system loses energy
63
Welectrical can also be =
- zF x E*cell MAX ELECTRICAL WORK THAT CAN BE TRANSFERRED
64
when does cell voltage = E*cell
resistance in circuit is large zero current flows
65
what must occur for the cell to do work
resistance must be lowered so current can flow
66
change in gibbs energy is equal to whattttt
-zF x E*cell equal to the max amount of work a cell can do G = -zF x E*cell
67
considering gibbs and cell potential,, what values must they have and how are they linked
Wele = -zF x E*cell E*cell = spontaneous if positive G = -zF x E*cell gibbs = max work a cell can do gibbs: spontaneous if negative
68
what conditions is maximum work done in
done in reversible conditions
69
what are reversible conditions when it comes to cells
high resistance little current measured Voltage = E*cell
70
faraday constant units
C mol-1
71
E*cell units
V
72
z units
no units
73
so G = -zF x E*cell units
CVmol-1 CV = J so G = Jmol-1
74
spontaneous Ecell must be
positive
75
spontaneous reaction must be
negative gibbs
76
gibbs and thermodynamic equilibrium are related in which equation,, and what does this tell us
G = -RT ln(K) tells us we can use the E*cell to find equilibrium constant, K
77
how can we use E*cell to find equilibrium constant K
G = -zF x E*cell G = -RT ln(k) -zF x E*cell = - RT ln(k) E*cell = RT/zF ln(k) ln(K) = zF/RT E*cell
78
what happens when a cell reaction reaches equilibrium
it goes flat it runs out current is drawn from the cell, the half cell reactions occur, concentration of species changes,, then concentration of species stops changing + no current flows. state where half cell reaction concentrations stop changing + no more current flows.
79
what does a large equ constant, K mean
it means that the reaction basically goes to completion,, all solid X forms Xions all Y ions form Y solids. there is complete conversion
80
what if the value of k is 1
reaction is at equilibrium
81
what if k is less than 1
the reaction is spontaneous in the reverse direction
82
E*cell dependence on concentration
E*cells are calculated under standard conditions,, they may change with different concentrations or gas pressures
83
how do we tackle the problem of E*cells being affected by conc and pressure
consider how Gibbs changes with rea and pro activity G = G* + RTln(Q)
84
what is Q
reaction quotient product of (activity x product ^stoich) // product of (activity of reactants ^ stoich) r
85
what does product of mean
it means u multiply the different things together. like sum of but with multiplication instead of addition
86
what is the activity of a solid
1
87
Q = K when
at equilibrium!!
88
what is the activity of a gas, a liquid and a solid
gas : p/p*. pressure of gas / 1bar liquid: conc/conc* conc/ 1moldm-3 solid = 1
89
finding the cell potential when conditions aren’t standard
Ecell = E*cell - (RT/zF) x ln(Q)
90
activity for stuff at standard conditions
1!!!
91
G = G* + RTln(Q) can be written as
-zF x Ecell = -zF x E*cell + RTln(Q)
92
nernst equation
Ecell = E*cell - RT/zF x ln(Q)
93
what does the nernst equation allow us to do
find the Ecell (cell potential) under non standard conditions find cell potential when changing the concentration of the cell can also find conc of species involved in an electrochemical cell.
94
what is a concentration cell
half cells made up of the same chemical reactions but at different concentrations
95
in electrochemical cells,, the chemical reactions are used to make what
used to produce energy
96
what is electrolysis
driving a chemical reaction by supplying it with electrical energy
97
input of energy allows what reactions to occur
non spontaneous reactions occur
98
what cells include reversible reactions that can be recharged
secondary cells
99
which battery is used in motor vehicles
lead - acid battery
100
electrolysis cell
looks like 1 half cell but is connected to an electrical power source (battery)

electrochemistry (11 decks)

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