Unit 3 AOS 2 Flashcards Preview

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Flashcards in Unit 3 AOS 2 Deck (125):
1

Electrolysis is used for (4)

extracting metals, making jewellery, protecting metal, recharging batteries

2

Define electrolysis

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

3

How does electrolysis work

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

4

Define electrolytes

liquids that can conduct electricity

5

Where do positive ions gain electrons

cathode

6

Where do negative ions lose electrons

anode

7

Define electrolytic cell

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.

8

Features of an electrolytic cell

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

9

What type of current is the electron flow

DC

10

Polarity of cathode in electrolysis

negative

11

Polarity of anode in electrolysis

positive

12

What occurs at anode and cathode (reduction/oxidation)

reduction at cathode, oxidation at anode

13

Where are cations and anions attracted

cations to cathode, anions to anode

14

Why is cathode negative

the external DC source forces electrons onto it.

15

Why is the anode positive

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

16

How are polarities determined in galvanic cell

spontaneous reaction

17

Factors affecting the electrolysis (3)

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

18

What happens to E naught when conditions aren’t standard

the standard the E naught values change

19

Why is electrolysis important

electrolysis provides the only practical way to prepare many metals

20

What reactive gases are prepared through electrolysis

fluorine, chlorine, sodium hydroxide

21

Define electroplating

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

22

Why is electroplating used

to make metal durable, protection from corrosion, attractive

23

Factors affecting quality of metal coating

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.

24

What might happen in electroplating if conditions aren’t satisfactory

metal coating powdery and drops off

25

Why must cleaning acids and bases be replaced

contamination/dirty

26

Name for when using electrolysis to extract metal

electro-refining

27

What is Hall-Heroult method used for

aluminium production using molten aluminium

28

Why can’t the aluminium be aqueous

water would be reduced

29

Membrane cell

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.

30

Faraday’s 1st law of electrolysis

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.

31

What is an ammeter

measures rate at which charge flows in a circuit

32

How many electrons per Q

6.24*10^18 electrons

33

Faraday’s constant

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

34

Faraday’s constant

96500 C mol-1

35

Faraday’s 2nd law of electrolysis

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

36

What is a lead-acid accumulator

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

37

Define recharging

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.

38

What is a lithium ion cell

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

39

What happens to lithium ion cells at high temp

‘thermal runaway’

40

Most common secondary cell

is lead-acid battery

41

Silver and gold are… (poor or good conductors)

poor conductors

42

How to find Kc when reaction reversed

1/Kc

43

How to find Kc when reaction coefficient doubled

Kc^2

44

How to find Kc when reaction coefficient halved

square root Kc

45

Formula to find charge

Q=It

46

What does Q stand for

charge in C

47

What does I stand for

current in amps

48

What does t stand for

time in seconds

49

Formula for moles and Q

n=Q/f

50

Factors affecting battery life (4)

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

51

What does molten mean

ions are separated

52

Can you electrolyse water

can’t unless salt dissolved in water

53

Positions of strongest oxidant/reductant

strongest oxidant - top right, strongest reductant - bottom left

54

How to determine electrolysis equation

pick strongest oxidant and reductant

55

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

the ion will be more likely to react.

56

Equilibrium reaction

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

Homogenous equations

all species have same states

58

Heterogenous equations

species have different states

59

The equilibrium law

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

60

Equilibrium constant

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

The reaction quotient Q

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

What is M

mol/L

63

If the value is high

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

64

If the value is small

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

65

Only factor that affects Kc

temperature

66

Why is temperature the only factor that affects Kc

changing energy available to system

67

What is extent (3)

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

What is rate of a reaction

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

69

Why doesn’t catalysts affect Kc

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

70

Why we need reaction quotient

for slower equations. AKA concentration fraction.

71

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

net back reaction

72

Le chatelier’s principle

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

73

How equilibrium can be disturbed (3)

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

74

Adding/removing reactants effect on equilibrium

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

75

Shift to right means

forward reaction favoured

76

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

physical or chemical means

77

Concentration of solids and liquids for Q equation is...

1

78

How does volume that increases concentration affect equilibrium

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

79

How does volume that decreases concentration affect equilibrium

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

80

Increase in volume example

dilution

81

Increase temperature effect on Kc (exo+endo)

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

82

Decrease temperature effect on Kc

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

83

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

effect on concentration without sudden change

84

What is yield

amount of product

85

How to calculate yield

actual mass obtained/theoretical maximum mass * 100

86

Other reasons for not 100% yield

practical how it is done, slow reaction

87

Haemoglobin

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

88

2 types of haemoglobin

oxyhaemoglobin, carboxyhaemoglobin

89

Why does carbon monoxide replace O2

much more extent of reaction of carbon monoxide

90

What is a reversible reaction

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

91

What is an irreversible reactions

reactions that can only go forward.

92

What is an open system

exchange energy and matter with their surroundings

93

What is a closed system

only exchange energy with their surroundings.

94

Why concentration doesn’t affect equilibrium constant

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

95

Why is CO poisoning fatal

can’t transport oxygen to cells

96

More energy a collision has means

the more dramatic are the changes produced

97

What is activation energy

The minimum energy required by reactants in order to react

98

Where can the activation energy come from

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

99

What is change in enthalpy + what is it denoted by

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

100

Define exothermic reaction

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

Define endothermic reaction

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

What 3 things are in the collision theory

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

103

How chemical reactions rates are measured

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

A Maxwell–Boltzmann distribution curve shows…

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

Is a Maxwell–Boltzmann symmetrical

It is not symmetrical.

106

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

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

107

What does the area under the Maxwell–Boltzmann graph represent

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

108

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

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

Factors that affect the rate of a reaction

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

110

Increasing concentration results in what for a reaction

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

111

Increasing pressure results in what for a reaction

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

112

Increasing the temperature means what for a reaction

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

Define catalyst

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

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

negative catalyst or inhibitor

115

Does catalyst alter delta H

no

116

Example of biological catalysts

enzyme

117

How are catalytic converters used

car exhausts

118

How does surface area affect reaction

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

What are the two types of catalysts

homogenous catalysts, heterogenous catalysts

120

What are homogenous catalysts

a catalyst with the same state as the reactants

121

What are heterogenous catalysts

a catalyst with a different physical state to the reactants
sufficiently energetic

122

How to increase collisions that occur in reaction

temp, concentration, SA

123

How to increase proportion of particles reacting

temp, catalyst,

124

At absolute zero for Maxwell-Boltzman graph

graph at 0

125

When adding equations what do you do to Kc

multiply Kc