Equilibrium Flashcards
(106 cards)
1
Q
In reversible reactions, what is initially present?
A
Reactants
2
Q
What isn’t initially present in reversible reactions?
A
No product
3
Q
The rate of the forward reaction begins ……
A
Quickly
4
Q
What happens after time to the speed of the forward reaction?
A
Decreases
5
Q
Initially the rate of reverse reaction is …..
A
Non-existent
6
Q
What happens after time to the reverse reactions?
A
Increases
7
Q
Why does the rate of the reverse reaction increase over time?
A
As more product is formed
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.
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.
10
Q
First stage of chemical equilibrium
A
- No products
- High rate of collisions between A and B
- Rate of forward reaction HIGH
11
Q
Stages 2 and 3 of chemical equilibrium
A
- Products formed
- Collisions between reactants decrease
- Rate of forward reaction DECREASES
- Reverse reaction begins
12
Q
Stage 4 of chemical equilibrium
A
- Rate of forward reaction EQUAL to rate of reverse reaction
- Dynamic equilibrium established
- Concentrations constant
13
Q
Is there a limiting reactant?
A
No
14
Q
Why is there no limiting reactant?
A
- No reactant runs out
- Reactions are reversible
15
Q
What plays the most important role in the reaction?
A
Temperature
16
Q
What does system mean?
A
The reaction
17
Q
Does the reaction ever stop/cease?
A
No
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.
19
Q
What does the fact that the reaction hasn’t stopped mean?
A
In a state of dynamic equilibrium
20
Q
When is the reaction considered ‘finished’?
A
When the reaction has reached equilibrium
21
Q
What do the amounts of reactants and products remain constant at?
A
The temperature that the reaction was carried out.
22
Q
Define dynamic equilibrium
A
Both the forward and reverse reactions occur at the same time.
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.
24
Q
What will be favoured if a substance is removed (decreased in concentration)?
A
The one that makes that substance.
25
What will be favoured if a substance is added (increase in concentration)?
The one that uses up that substance.
26
N2 + 3H2 ⇌ 2NH3
| State and explain the effect on the position of equilibrium when more NH3 is added.
The position of equilibrium will move to the LEFT favouring the REVERSE reaction so as to use up the extra NH3 that was added.
27
N2 + 3H₂ ⇌ 2NH3
| State and explain the effect on the position of equilibrium when some N2 is removed.
The position of equilibrium will move to the LEFT favouring the REVERSE reaction so as to make more N2.
28
What reaction will be favoured if the temperature is decreased?
Exothermic reaction
29
Why is the exothermic reaction favoured if the temperature is decreased?
Because exothermic reactions give out heat and this heat will replace the heat that was removed.
30
What reaction will be favoured if the temperature is increased?
The endothermic reaction
31
Why is the endothermic reaction favoured if the temperature is increased?
Because endothermic reactions take in heat and this will remove the extra heat was given to the system.
32
△H = negative
Exothermic
33
△H = positive
Endothermic
34
N₂ +3H₂ ⇌ 2NH3 △H = -92J/mol
| State and explain the effect on the position of equilibrium if the temperature is increased.
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.
35
N₂ +3H₂ ⇌ 2NH3 △H = -92J/mol
| State and explain the effect on the position of equilibrium if the temperature is decreased.
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.
36
What is decided first in an equation?
Which are exothermic and endothermic reactions.
37
If the heat change is 0, what can be said about temperature change?
A change in temperature will not change the position of equilibrium.
38
If the pressure is increased what side will the system favour?
The side with the LEAST number of moles.
39
Why will the system favour the side with the least number of moles if pressure is increased?
As it will bring the pressure back down.
40
If the pressure is decreased, what side will the system favour?
The side with the MOST number of moles.
41
Why will the system favour the side with the MOST number of moles if pressure is decreased?
As it will bring the pressure back up.
42
N₂ + 3H₂ ⇌ 2NH3
| State and explain the effect on the position of equilibrium on the above systems when the pressure is increased.
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.
43
N₂ + 3H₂ ⇌ 2NH3
| State and explain the effect on the position of equilibrium on the above systems when the pressure is decreased.
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
Increased favours
Endothermic
45
Decreased favours
Exothermic
46
What systems can pressure be used for?
GASEOUS ONLY
47
What happens when there are equal numbers of moles on both side of the equation?
H₂ + I₂ ⇌ 2HI
TRICK Q - Changes in pressure never have an effect on systems that are not gaseous.
48
A top heavy fraction
Kc will be greater than 1, hence we can see that there was more RHS than LHS present at equilibrium.
49
A bottom heavy fraction
Kc will be less than 1, hence we can see that there was LHS than RHS present at equilibrium.
50
What is the value of Kc dependant on?
Temperature
51
What will happen if the temperate changes?
The value of Kc will change too.
52
What is the only factor that will ever cause a change on the value of Kc?
Temperature.
53
Type 1
Asked to calculate Kc
54
Type 2
Will be given Kc
55
If the equation is halved, what happens to Kc
square rooted
56
If the equation is in reverse what happens to Kc
1/old Kc
57
equation is doubled, Kc
squaed
58
To investigated Le Chatelier's principle
| equation
Fe3+ + CNS- = Fe(CNS)2+
59
To investigated Le Chatelier's principle
| Fe+3
Iron (III) chloride
60
To investigated Le Chatelier's principle
| CNS-
potassium thiocyanate
61
To investigated Le Chatelier's principle
| what colour is Iron (III) chloride
yellow
62
To investigated Le Chatelier's principle
| what colour is potassium thiocyanate
colourless
63
To investigated Le Chatelier's principle
| what colour is Fe(CNS)2+
red
64
To investigated Le Chatelier's principle
| first step
a solution of Iron (III) chloride and potassium thiocyanate were mixed together in a boiling tube (red)
65
To investigated Le Chatelier's principle
| solution is ready
add some hydrochloric acid (yellow observed)
66
To investigated Le Chatelier's principle
| explain why it went yellow when hydrochloric acid was added
position of equilibrium moved to the left, favouring the reverse reaction to use up extra Cl-
67
To investigated Le Chatelier's principle
| what is added after HCl
Iron (III) chloride is added (red)
68
To investigated Le Chatelier's principle
| investigate with temperature
placed in a beaker of boiling water
69
To investigated Le Chatelier's principle
| when placed in boiling water
reverse reaction is favoured (endothermic)
| increase -> endothermic
70
2 industrial applications of Le Chatelier's Principle
The Haber process for the manufacture of ammonia
| The contact process for the manufacture of sulfuric acid
71
The Haber process for the manufacture of ammonia
| equation
N2 + 3H2 = 2NH3
72
The Haber process for the manufacture of ammonia
| explain how they get the nitrogen
obtained from air
| air is liquified and then fractionally distilled
73
The Haber process for the manufacture of ammonia
| how do they get the hydrogen
steam reforming of natural gas - mainly methane
74
The Haber process for the manufacture of ammonia
| catalyst and promoter used
catalyst; finely divided iron
| promoter; aluminium oxide
75
The Haber process for the manufacture of ammonia
| advantages of a catalyst and a promoter
equilibrium is reached faster and lower temperatures can be used
76
The Haber process for the manufacture of ammonia
| ideal temperature for this reaction and why
low temperature as it will favour the exothermic reaction
77
The Haber process for the manufacture of ammonia
| proble, with low temperature
slow reaction
| a compromise has to be reached
78
The Haber process for the manufacture of ammonia
| temperature used
about 500ºC
79
The Haber process for the manufacture of ammonia
| ideal pressure and why
high pressure, 2 moles on right, high pressure will favour the side with the least number of moles
80
The Haber process for the manufacture of ammonia
| problem with high pressure
costly to build and maintain a high pressure plant
| a compromise has to be reached
81
The Haber process for the manufacture of ammonia
| pressure used
200 atm
82
4 uses of ammonia
to make:
| fertilisers, cleaning agents, explosives and nitric acid
83
where is ammonia manufactured in Ireland
at the IFI plant in Cobh, Co.Cork
84
The contact process for the manufacture of sulfuric acid
| how many stages are there
3
85
The contact process for the manufacture of sulfuric acid
| what occurs in stage 1
sulfur is burned in oxygen to produce sulfur dioxide
86
The contact process for the manufacture of sulfuric acid
| equation for stage 1
S + O2 -> SO2
87
The contact process for the manufacture of sulfuric acid
| what happens in stage 2
sulfur dioxide is reacted with oxygen over a catalyst, they must be in close contact
88
The contact process for the manufacture of sulfuric acid
| stage 2 reaction
SO2 + 1/2 O2 = SO3
89
The contact process for the manufacture of sulfuric acid
| stage 2, is forward reaction endothermic or exothermic
exothermic
90
The contact process for the manufacture of sulfuric acid
| stage 2 catalyst
vanadium pentoxide V2O5
91
The contact process for the manufacture of sulfuric acid
| stage 2, the better catalyst and why it is not used
platinum is a better catalyst, but is easily poisoned by impurities such as arsenic in the reactants
92
The contact process for the manufacture of sulfuric acid
| stage 2 , ideal pressure
high pressure
93
The contact process for the manufacture of sulfuric acid
| stage 2 actual presure
4-7 atms, just above atmospheric pressure
94
The contact process for the manufacture of sulfuric acid
| problem with high pressure 2
expensive
| causes sulfur dioxide to liquefy
95
The contact process for the manufacture of sulfuric acid
| stage 2, ideal temperature
low temperature
| forward reaction exothermic
96
The contact process for the manufacture of sulfuric acid
| problem with low temp
slow reaction
97
The contact process for the manufacture of sulfuric acid
| actual temperature
450ºC
98
The contact process for the manufacture of sulfuric acid
| what occurs in stage 3
sulfur trioxide is reacted with water to make sulfuric acid
99
The contact process for the manufacture of sulfuric acid
| stage 3 equation
SO3 + H2O -> H2SO4
100
The contact process for the manufacture of sulfuric acid
| stage 3, what happens if sulfur dioxide is reacted with water quickly
a mist of sufuric acid that will not condense forms over the water, the mist is dangerous
101
The contact process for the manufacture of sulfuric acid
| stage 3 how do you prevent mist from being made
sulfur trioxide is put in some sulfuric acid already made and then water is added
102
The contact process for the manufacture of sulfuric acid
| stage 3 how much water for how much sulfur trioxide
1 mole of water for every mole of sulfur trioxide
103
The contact process for the manufacture of sulfuric acid
| stage 3 too little water
not all sulfur trioxide will have reacted
104
The contact process for the manufacture of sulfuric acid
| stage 3 too much water
sulfuric acid becomes diluted
105
use of sulfuric acid 3
car batteries
detergents
paints
106
world consumption of sulfuric acid per year
160 million tonnes
