Unit 3 AOS 2 Flashcards

1
Q

Electrolysis is used for (4)

A

extracting metals, making jewellery, protecting metal, recharging batteries

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2
Q

Define electrolysis

A

process in which a current is used to make a non-spontaneous redox reaction occur.

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3
Q

How does electrolysis work

A

electricity passes through a molten ionic compound or through an electrolyte, external power source forces electrons to move in the reverse direction so reactions are reversed

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4
Q

Define electrolytes

A

liquids that can conduct electricity

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5
Q

Where do positive ions gain electrons

A

cathode

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6
Q

Where do negative ions lose electrons

A

anode

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7
Q

Define electrolytic cell

A

An electric cell in which a non-spontaneous redox reaction is made to occur by the application of an external potential difference across the electrodes.

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8
Q

Features of an electrolytic cell

A

electrolyte solution with free-moving ions which allow electrons to flow through external circuit, two electrodes, external source of electrons

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9
Q

What type of current is the electron flow

A

DC

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10
Q

Polarity of cathode in electrolysis

A

negative

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11
Q

Polarity of anode in electrolysis

A

positive

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12
Q

What occurs at anode and cathode (reduction/oxidation)

A

reduction at cathode, oxidation at anode

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13
Q

Where are cations and anions attracted

A

cations to cathode, anions to anode

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14
Q

Why is cathode negative

A

the external DC source forces electrons onto it.

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15
Q

Why is the anode positive

A

The anode is positive because the DC source withdraws electrons from it.

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16
Q

How are polarities determined in galvanic cell

A

spontaneous reaction

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17
Q

Factors affecting the electrolysis (3)

A

concentration of electrolyte, nature of the electrolyte, the nature of the electrodes

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18
Q

What happens to E naught when conditions aren’t standard

A

the standard the E naught values change

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19
Q

Why is electrolysis important

A

electrolysis provides the only practical way to prepare many metals

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20
Q

What reactive gases are prepared through electrolysis

A

fluorine, chlorine, sodium hydroxide

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21
Q

Define electroplating

A

thin coating of metal is applied to more common base metal through electrolysis

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22
Q

Why is electroplating used

A

to make metal durable, protection from corrosion, attractive

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23
Q

Factors affecting quality of metal coating

A

concentration of cations to be reduced, unwanted side reactions must be avoided, type and concentration of electrolyte needs careful consideration, solution must contain compounds to control the acidity and increase the conductivity, it needs to be considered whether the metal coating makes colour brighter and smoother, in many electroplating cells the anode must be shaped like the object at the cathode to achieve an even metal coating.

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24
Q

What might happen in electroplating if conditions aren’t satisfactory

A

metal coating powdery and drops off

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25
Q

Why must cleaning acids and bases be replaced

A

contamination/dirty

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26
Q

Name for when using electrolysis to extract metal

A

electro-refining

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27
Q

What is Hall-Heroult method used for

A

aluminium production using molten aluminium

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28
Q

Why can’t the aluminium be aqueous

A

water would be reduced

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29
Q

Membrane cell

A

electrolysis of brine (aqueous NaCl) - to produce Cl, H gases and NaOH. Semi-permeable plastic membrane separates anode half-cell from cathode half-cell, and traps chloride and water but not sodium and hydroxide.

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30
Q

Faraday’s 1st law of electrolysis

A

the amount of any substance deposited, evolved or dissolved at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the cell.

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31
Q

What is an ammeter

A

measures rate at which charge flows in a circuit

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32
Q

How many electrons per Q

A

6.24*10^18 electrons

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33
Q

Faraday’s constant

A

A constant that represents the amount of electric charge carried by 1 mole of electrons.

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34
Q

Faraday’s constant

A

96500 C mol-1

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35
Q

Faraday’s 2nd law of electrolysis

A

to produce 1 mol of a substance by electrolysis, a certain number of moles of electrons (Faraday’s) must be consumed according to the relevant half equations

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36
Q

What is a lead-acid accumulator

A

A battery with lead electrodes using dilute sulfuric acid as the electrolyte; each cell generates about 2 volts.

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37
Q

Define recharging

A

Forcing electrons to travel in the reverse direction and, because the discharge products are still in contact with the electrodes, the original reactions are reversed.

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38
Q

What is a lithium ion cell

A

A battery where lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.

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39
Q

What happens to lithium ion cells at high temp

A

‘thermal runaway’

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40
Q

Most common secondary cell

A

is lead-acid battery

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41
Q

Silver and gold are… (poor or good conductors)

A

poor conductors

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42
Q

How to find Kc when reaction reversed

A

1/Kc

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43
Q

How to find Kc when reaction coefficient doubled

A

Kc^2

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44
Q

How to find Kc when reaction coefficient halved

A

square root Kc

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45
Q

Formula to find charge

A

Q=It

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46
Q

What does Q stand for

A

charge in C

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47
Q

What does I stand for

A

current in amps

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48
Q

What does t stand for

A

time in seconds

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49
Q

Formula for moles and Q

A

n=Q/f

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50
Q

Factors affecting battery life (4)

A

increase in temperature, overcharging (may not fully recharged/discharged, or reduce insulation - short circuits and danger of explosion), products of discharge fall from electrodes and when no contact reverse reaction cannot occur, corrosion due to acidic environment or constant use

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51
Q

What does molten mean

A

ions are separated

52
Q

Can you electrolyse water

A

can’t unless salt dissolved in water

53
Q

Positions of strongest oxidant/reductant

A

strongest oxidant - top right, strongest reductant - bottom left

54
Q

How to determine electrolysis equation

A

pick strongest oxidant and reductant

55
Q

If a solution is of high concentration (such as >6M)…

A

the ion will be more likely to react.

56
Q

Equilibrium reaction

A

A reaction where a chemical equilibrium is reached. This is the state in which both reactants and products are present in concentrations that have no further tendency to change with time.

57
Q

Homogenous equations

A

all species have same states

58
Q

Heterogenous equations

A

species have different states

59
Q

The equilibrium law

A

The relationship between the concentrations of the products and the reactants, taking into account their stoichiometric values.

60
Q

Equilibrium constant

A

The value of the concentration fraction at equilibrium; also called the equilibrium constant, Kc. It allows us to describe the position of the chemical equilibrium quantitatively.

61
Q

The reaction quotient Q

A

is the measure of the concentrations of the products and reactants at any particular time. Ratio of concentrations of the products divided by the concentrations of the reactants.

62
Q

What is M

A

mol/L

63
Q

If the value is high

A

(greater than 10^4) large extent, favours forward

64
Q

If the value is small

A

(less than 10^-4) small extent, favours backwards

65
Q

Only factor that affects Kc

A

temperature

66
Q

Why is temperature the only factor that affects Kc

A

changing energy available to system

67
Q

What is extent (3)

A

the degree to which reactants are converted into products. How far the reaction goes. Some reactions will occur completely, some will never be complete, how much product is formed when the system reaches equilibrium.

68
Q

What is rate of a reaction

A

an indication of how fast it occurs. The rate shows how long it takes to establish the position of equilibrium.

69
Q

Why doesn’t catalysts affect Kc

A

alters the time taken to get to equilibrium, not the position of it.

70
Q

Why we need reaction quotient

A

for slower equations. AKA concentration fraction.

71
Q

If Q is bigger than Kc… (is the reaction net forwards or backwards)

A

net back reaction

72
Q

Le chatelier’s principle

A

When a change is made to an equilibrium system, the system moves to counteract the imposed change and restore the system to equilibrium.

73
Q

How equilibrium can be disturbed (3)

A

adding/removing substance involved, changing volume at constant temp, changing temp

74
Q

Adding/removing reactants effect on equilibrium

A

concentrations will be different from original values, but value of equilibrium constant unchanged

75
Q

Shift to right means

A

forward reaction favoured

76
Q

Removal of reactants/products can be achieved through what types of means?

A

physical or chemical means

77
Q

Concentration of solids and liquids for Q equation is…

A

1

78
Q

How does volume that increases concentration affect equilibrium

A

to decrease this, the system reacts in the direction that produces fewer particles.

79
Q

How does volume that decreases concentration affect equilibrium

A

to increase this concentration, the system must react in the direction that produces more particles if it is to re-establish equilibrium.

80
Q

Increase in volume example

A

dilution

81
Q

Increase temperature effect on Kc (exo+endo)

A

exothermic backwards favoured and Kc decreases, endothermic forwards favoured, and Kc increases

82
Q

Decrease temperature effect on Kc

A

exothermic forwards favoured, and Kc increases, endothermic backwards favoured and Kc decreases,

83
Q

What does change in temp look like on concentration-time graphs

A

effect on concentration without sudden change

84
Q

What is yield

A

amount of product

85
Q

How to calculate yield

A

actual mass obtained/theoretical maximum mass * 100

86
Q

Other reasons for not 100% yield

A

practical how it is done, slow reaction

87
Q

Haemoglobin

A

The oxygen-carrying pigment and predominant protein in red blood cells.

88
Q

2 types of haemoglobin

A

oxyhaemoglobin, carboxyhaemoglobin

89
Q

Why does carbon monoxide replace O2

A

much more extent of reaction of carbon monoxide

90
Q

What is a reversible reaction

A

reaction that can go both forwards and backwards - reactants form products and products can form the same reactants

91
Q

What is an irreversible reactions

A

reactions that can only go forward.

92
Q

What is an open system

A

exchange energy and matter with their surroundings

93
Q

What is a closed system

A

only exchange energy with their surroundings.

94
Q

Why concentration doesn’t affect equilibrium constant

A

By changing the concentration, we simply only redistribute the energy available.

95
Q

Why is CO poisoning fatal

A

can’t transport oxygen to cells

96
Q

More energy a collision has means

A

the more dramatic are the changes produced

97
Q

What is activation energy

A

The minimum energy required by reactants in order to react

98
Q

Where can the activation energy come from

A

can come from thermal energy, kinetic energy of colliding particles.

99
Q

What is change in enthalpy + what is it denoted by

A

The amount of energy released or absorbed in a chemical reaction. Denoted by delta H.

100
Q

Define exothermic reaction

A

Describes a chemical reaction in which energy is released to the surroundings. For exothermic reactions, the activation energy is less than the energy released when new bonds form. Consequently, there is a net release of energy (usually as heat released to the surroundings).

101
Q

Define endothermic reaction

A

Describes a chemical reaction in which energy is absorbed from the surroundings. For endothermic reactions, the activation energy is greater than the energy released when new bonds form. Consequently, there is a net input of energy (in most cases, heat is absorbed from the surroundings).

102
Q

What 3 things are in the collision theory

A

particles must collide, have the correct orientation for bond breaking to occur, have sufficient energy for the reaction to occur.

103
Q

How chemical reactions rates are measured

A

volume of gas evolved, mass of solid formed, decrease in mass due to gas evolving, intensity of colour of solution, formation of a precipitate, pH, temperature.

104
Q

A Maxwell–Boltzmann distribution curve shows…

A

the number of particles with a particular energy graphed against the value of that energy. During a reaction at a given temperature, only a small proportion of the reactant particles have kinetic energy that is equal to or greater than the activation energy and so are able to react. The particles in a sample have a wide range of kinetic energies. As kinetic energy is given by the formula 1/2mv^2, this means that there is also a range of velocities. This is due to the collisions that the particles are constantly undergoing.

105
Q

Is a Maxwell–Boltzmann symmetrical

A

It is not symmetrical.

106
Q

What does the highest point represent in a Maxwell–Boltzmann graph symbolise

A

The highest point represents the most probable velocity, however this is not the same as the average velocity.

107
Q

What does the area under the Maxwell–Boltzmann graph represent

A

The area under the graph represents the total number of particles in the sample.

108
Q

The effect of increasing the temperature on a Maxwell–Boltzmann graph

A

is to ‘stretch’ (not move) the graph to the right. As a result, there are more particles with higher kinetic energies and on average they all move faster and the average kinetic energy is higher.

109
Q

Factors that affect the rate of a reaction

A

concentration, pressure, temperature, catalysts, catalytic converters, the effect off surface area,

110
Q

Increasing concentration results in what for a reaction

A

an increased frequency of successful collisions during any given period of time and hence a higher rate of reaction.

111
Q

Increasing pressure results in what for a reaction

A

more crowding together of the particles and hence more successful collisions within a certain time.

112
Q

Increasing the temperature means what for a reaction

A

there are more particles with enough energy to overcome the activation energy barrier. Another effect of increasing the temperature is that there is an increased frequency of collisions due to the particles moving faster. However, a more sophisticated analysis of the situation reveals that this is secondary to the effect of the energy distributions mentioned above.

113
Q

Define catalyst

A

A substance that alters the rate of a reaction through providing an alternative reaction pathway with a lower activation energy which increases the proportion of collisions with energy greater than the activation energy; without a change in its own concentration

114
Q

What is a catalyst called if it is used to slow down reaction

A

negative catalyst or inhibitor

115
Q

Does catalyst alter delta H

A

no

116
Q

Example of biological catalysts

A

enzyme

117
Q

How are catalytic converters used

A

car exhausts

118
Q

How does surface area affect reaction

A

by increasing the surface area, more of a substance is brought into contact with other substances with which it might react. In terms of collision theory, an increase in surface area means that more reactant particles can collide with one another and, therefore, there are more successful collisions between them in a given period of time. This leads to an increased rate of reaction.

119
Q

What are the two types of catalysts

A

homogenous catalysts, heterogenous catalysts

120
Q

What are homogenous catalysts

A

a catalyst with the same state as the reactants

121
Q

What are heterogenous catalysts

A

a catalyst with a different physical state to the reactants

sufficiently energetic

122
Q

How to increase collisions that occur in reaction

A

temp, concentration, SA

123
Q

How to increase proportion of particles reacting

A

temp, catalyst,

124
Q

At absolute zero for Maxwell-Boltzman graph

A

graph at 0

125
Q

When adding equations what do you do to Kc

A

multiply Kc