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chemistry (tara) > Equilibrium > Flashcards

Equilibrium Flashcards

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1
Q

In reversible reactions, what is initially present?

A

Reactants

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2
Q

What isn’t initially present in reversible reactions?

A

No product

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3
Q

The rate of the forward reaction begins ……

A

Quickly

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4
Q

What happens after time to the speed of the forward reaction?

A

Decreases

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5
Q

Initially the rate of reverse reaction is …..

A

Non-existent

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6
Q

What happens after time to the reverse reactions?

A

Increases

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7
Q

Why does the rate of the reverse reaction increase over time?

A

As more product is formed

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8
Q

What stage will eventually be reached after time when the rate of reverse reaction has sped up the rate of the forward reaction has decreased?

A

The rate of forward reaction will equal the rate of reverse reaction.

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9
Q

What is said when the rate of reverse reaction equals the rate of forward reaction?

A

Said to have reacted a state of equilibrium.

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10
Q

First stage of chemical equilibrium

A
  • No products
  • High rate of collisions between A and B
  • Rate of forward reaction HIGH
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11
Q

Stages 2 and 3 of chemical equilibrium

A
  • Products formed
  • Collisions between reactants decrease
  • Rate of forward reaction DECREASES
  • Reverse reaction begins
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12
Q

Stage 4 of chemical equilibrium

A
  • Rate of forward reaction EQUAL to rate of reverse reaction
  • Dynamic equilibrium established
  • Concentrations constant
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13
Q

Is there a limiting reactant?

A

No

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14
Q

Why is there no limiting reactant?

A
  • No reactant runs out

- Reactions are reversible

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15
Q

What plays the most important role in the reaction?

A

Temperature

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16
Q

What does system mean?

A

The reaction

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17
Q

Does the reaction ever stop/cease?

A

No

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18
Q

Define chemical equilibrium

A

A system is said to have reached a state of equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

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19
Q

What does the fact that the reaction hasn’t stopped mean?

A

In a state of dynamic equilibrium

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20
Q

When is the reaction considered ‘finished’?

A

When the reaction has reached equilibrium

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21
Q

What do the amounts of reactants and products remain constant at?

A

The temperature that the reaction was carried out.

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22
Q

Define dynamic equilibrium

A

Both the forward and reverse reactions occur at the same time.

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23
Q

Define Le Chatelier’s principle

A

When a system at equilibrium is subjected to a stress such as a change in temperature, pressure or concentration the system will alter to oppose the effect of the stress.

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24
Q

What will be favoured if a substance is removed (decreased in concentration)?

A

The one that makes that substance.

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25
Q

What will be favoured if a substance is added (increase in concentration)?

A

The one that uses up that substance.

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26
Q

N2 + 3H2 ⇌ 2NH3

State and explain the effect on the position of equilibrium when more NH3 is added.

A

The position of equilibrium will move to the LEFT favouring the REVERSE reaction so as to use up the extra NH3 that was added.

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27
Q

N2 + 3H₂ ⇌ 2NH3

State and explain the effect on the position of equilibrium when some N2 is removed.

A

The position of equilibrium will move to the LEFT favouring the REVERSE reaction so as to make more N2.

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28
Q

What reaction will be favoured if the temperature is decreased?

A

Exothermic reaction

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29
Q

Why is the exothermic reaction favoured if the temperature is decreased?

A

Because exothermic reactions give out heat and this heat will replace the heat that was removed.

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30
Q

What reaction will be favoured if the temperature is increased?

A

The endothermic reaction

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31
Q

Why is the endothermic reaction favoured if the temperature is increased?

A

Because endothermic reactions take in heat and this will remove the extra heat was given to the system.

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32
Q

△H = negative

A

Exothermic

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33
Q

△H = positive

A

Endothermic

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34
Q

N₂ +3H₂ ⇌ 2NH3 △H = -92J/mol

State and explain the effect on the position of equilibrium if the temperature is increased.

A

The position of the equilibrium will move to the LEFT favouring the REVERSE reaction as it is endothermic and will use up the extra heat that was added.

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35
Q

N₂ +3H₂ ⇌ 2NH3 △H = -92J/mol

State and explain the effect on the position of equilibrium if the temperature is decreased.

A

The position of equilibrium will move to the RIGHT favouring the FORWARD reaction, as it is exothermic and will replace the heat that was removed.

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36
Q

What is decided first in an equation?

A

Which are exothermic and endothermic reactions.

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37
Q

If the heat change is 0, what can be said about temperature change?

A

A change in temperature will not change the position of equilibrium.

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38
Q

If the pressure is increased what side will the system favour?

A

The side with the LEAST number of moles.

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39
Q

Why will the system favour the side with the least number of moles if pressure is increased?

A

As it will bring the pressure back down.

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40
Q

If the pressure is decreased, what side will the system favour?

A

The side with the MOST number of moles.

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41
Q

Why will the system favour the side with the MOST number of moles if pressure is decreased?

A

As it will bring the pressure back up.

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42
Q

N₂ + 3H₂ ⇌ 2NH3

State and explain the effect on the position of equilibrium on the above systems when the pressure is increased.

A

The position of equilibrium will move to the RIGHT favouring the FORWARD reaction as the forward reaction produces less moles which will bring the pressure down again.

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43
Q

N₂ + 3H₂ ⇌ 2NH3

State and explain the effect on the position of equilibrium on the above systems when the pressure is decreased.

A

The position of equilibrium will move to the LEFT favouring the REVERSE reaction as the reverse reaction produces more moles, which will bring the pressure up again.

44
Q

Increased favours

A

Endothermic

45
Q

Decreased favours

A

Exothermic

46
Q

What systems can pressure be used for?

A

GASEOUS ONLY

47
Q

What happens when there are equal numbers of moles on both side of the equation?
H₂ + I₂ ⇌ 2HI

A

TRICK Q - Changes in pressure never have an effect on systems that are not gaseous.

48
Q

A top heavy fraction

A

Kc will be greater than 1, hence we can see that there was more RHS than LHS present at equilibrium.

49
Q

A bottom heavy fraction

A

Kc will be less than 1, hence we can see that there was LHS than RHS present at equilibrium.

50
Q

What is the value of Kc dependant on?

A

Temperature

51
Q

What will happen if the temperate changes?

A

The value of Kc will change too.

52
Q

What is the only factor that will ever cause a change on the value of Kc?

A

Temperature.

53
Q

Type 1

A

Asked to calculate Kc

54
Q

Type 2

A

Will be given Kc

55
Q

If the equation is halved, what happens to Kc

A

square rooted

56
Q

If the equation is in reverse what happens to Kc

A

1/old Kc

57
Q

equation is doubled, Kc

A

squaed

58
Q

To investigated Le Chatelier’s principle

equation

A

Fe3+ + CNS- = Fe(CNS)2+

59
Q

To investigated Le Chatelier’s principle

Fe+3

A

Iron (III) chloride

60
Q

To investigated Le Chatelier’s principle

CNS-

A

potassium thiocyanate

61
Q

To investigated Le Chatelier’s principle

what colour is Iron (III) chloride

A

yellow

62
Q

To investigated Le Chatelier’s principle

what colour is potassium thiocyanate

A

colourless

63
Q

To investigated Le Chatelier’s principle

what colour is Fe(CNS)2+

A

red

64
Q

To investigated Le Chatelier’s principle

first step

A

a solution of Iron (III) chloride and potassium thiocyanate were mixed together in a boiling tube (red)

65
Q

To investigated Le Chatelier’s principle

solution is ready

A

add some hydrochloric acid (yellow observed)

66
Q

To investigated Le Chatelier’s principle

explain why it went yellow when hydrochloric acid was added

A

position of equilibrium moved to the left, favouring the reverse reaction to use up extra Cl-

67
Q

To investigated Le Chatelier’s principle

what is added after HCl

A

Iron (III) chloride is added (red)

68
Q

To investigated Le Chatelier’s principle

investigate with temperature

A

placed in a beaker of boiling water

69
Q

To investigated Le Chatelier’s principle

when placed in boiling water

A

reverse reaction is favoured (endothermic)

increase -> endothermic

70
Q

2 industrial applications of Le Chatelier’s Principle

A

The Haber process for the manufacture of ammonia

The contact process for the manufacture of sulfuric acid

71
Q

The Haber process for the manufacture of ammonia

equation

A

N2 + 3H2 = 2NH3

72
Q

The Haber process for the manufacture of ammonia

explain how they get the nitrogen

A

obtained from air

air is liquified and then fractionally distilled

73
Q

The Haber process for the manufacture of ammonia

how do they get the hydrogen

A

steam reforming of natural gas - mainly methane

74
Q

The Haber process for the manufacture of ammonia

catalyst and promoter used

A

catalyst; finely divided iron

promoter; aluminium oxide

75
Q

The Haber process for the manufacture of ammonia

advantages of a catalyst and a promoter

A

equilibrium is reached faster and lower temperatures can be used

76
Q

The Haber process for the manufacture of ammonia

ideal temperature for this reaction and why

A

low temperature as it will favour the exothermic reaction

77
Q

The Haber process for the manufacture of ammonia

proble, with low temperature

A

slow reaction

a compromise has to be reached

78
Q

The Haber process for the manufacture of ammonia

temperature used

A

about 500ºC

79
Q

The Haber process for the manufacture of ammonia

ideal pressure and why

A

high pressure, 2 moles on right, high pressure will favour the side with the least number of moles

80
Q

The Haber process for the manufacture of ammonia

problem with high pressure

A

costly to build and maintain a high pressure plant

a compromise has to be reached

81
Q

The Haber process for the manufacture of ammonia

pressure used

A

200 atm

82
Q

4 uses of ammonia

A

to make:

fertilisers, cleaning agents, explosives and nitric acid

83
Q

where is ammonia manufactured in Ireland

A

at the IFI plant in Cobh, Co.Cork

84
Q

The contact process for the manufacture of sulfuric acid

how many stages are there

A

3

85
Q

The contact process for the manufacture of sulfuric acid

what occurs in stage 1

A

sulfur is burned in oxygen to produce sulfur dioxide

86
Q

The contact process for the manufacture of sulfuric acid

equation for stage 1

A

S + O2 -> SO2

87
Q

The contact process for the manufacture of sulfuric acid

what happens in stage 2

A

sulfur dioxide is reacted with oxygen over a catalyst, they must be in close contact

88
Q

The contact process for the manufacture of sulfuric acid

stage 2 reaction

A

SO2 + 1/2 O2 = SO3

89
Q

The contact process for the manufacture of sulfuric acid

stage 2, is forward reaction endothermic or exothermic

A

exothermic

90
Q

The contact process for the manufacture of sulfuric acid

stage 2 catalyst

A

vanadium pentoxide V2O5

91
Q

The contact process for the manufacture of sulfuric acid

stage 2, the better catalyst and why it is not used

A

platinum is a better catalyst, but is easily poisoned by impurities such as arsenic in the reactants

92
Q

The contact process for the manufacture of sulfuric acid

stage 2 , ideal pressure

A

high pressure

93
Q

The contact process for the manufacture of sulfuric acid

stage 2 actual presure

A

4-7 atms, just above atmospheric pressure

94
Q

The contact process for the manufacture of sulfuric acid

problem with high pressure 2

A

expensive

causes sulfur dioxide to liquefy

95
Q

The contact process for the manufacture of sulfuric acid

stage 2, ideal temperature

A

low temperature

forward reaction exothermic

96
Q

The contact process for the manufacture of sulfuric acid

problem with low temp

A

slow reaction

97
Q

The contact process for the manufacture of sulfuric acid

actual temperature

A

450ºC

98
Q

The contact process for the manufacture of sulfuric acid

what occurs in stage 3

A

sulfur trioxide is reacted with water to make sulfuric acid

99
Q

The contact process for the manufacture of sulfuric acid

stage 3 equation

A

SO3 + H2O -> H2SO4

100
Q

The contact process for the manufacture of sulfuric acid

stage 3, what happens if sulfur dioxide is reacted with water quickly

A

a mist of sufuric acid that will not condense forms over the water, the mist is dangerous

101
Q

The contact process for the manufacture of sulfuric acid

stage 3 how do you prevent mist from being made

A

sulfur trioxide is put in some sulfuric acid already made and then water is added

102
Q

The contact process for the manufacture of sulfuric acid

stage 3 how much water for how much sulfur trioxide

A

1 mole of water for every mole of sulfur trioxide

103
Q

The contact process for the manufacture of sulfuric acid

stage 3 too little water

A

not all sulfur trioxide will have reacted

104
Q

The contact process for the manufacture of sulfuric acid

stage 3 too much water

A

sulfuric acid becomes diluted

105
Q

use of sulfuric acid 3

A

car batteries
detergents
paints

106
Q

world consumption of sulfuric acid per year

A

160 million tonnes

chemistry (tara) (50 decks)

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