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Chemistry AS > equilibria > Flashcards

equilibria Flashcards

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1
Q
A
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2
Q

What is a reversible reaction?

A

A reaction where products can react to reform the original reactants

Indicated by opposing half arrows (⇌)

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3
Q

What does dynamic equilibrium mean?

A

The state where the rate of the forward reaction equals the rate of the backward reaction in a closed system

Concentrations of reactants and products remain constant

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4
Q

What characterizes a closed system in chemical reactions?

A

None of the reactants or products escape from the reaction mixture

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5
Q

How does an open system differ from a closed system in terms of chemical reactions?

A

Matter and energy can be lost to the surroundings in an open system

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6
Q

What happens to the position of equilibrium when the concentration of reactants increases?

A

Equilibrium shifts to the right

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7
Q

What is Le Chatelier’s Principle?

A

If a change is made to a system at dynamic equilibrium, the position of equilibrium shifts to minimize the change

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8
Q

What occurs to the equilibrium position when the concentration of a product increases?

A

Equilibrium shifts to the left

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9
Q

What effect does an increase in pressure have on a gaseous reaction?

A

Equilibrium shifts in the direction that produces a smaller number of gas molecules

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10
Q

What happens to the equilibrium when temperature is increased for an endothermic reaction?

A

Equilibrium shifts to the right

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11
Q

What is the role of a catalyst in a chemical reaction?

A

Increases the rate of both forward and reverse reactions equally, without affecting the position of equilibrium

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12
Q

What is the equilibrium expression for the reaction aA + bB ⇌ cC + dD?

A

Kc = [C]^c [D]^d / [A]^a [B]^b

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13
Q

What is a partial pressure?

A

The pressure that a gas would exert if it occupied the container alone

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14
Q

How is total pressure calculated from partial pressures?

A

Ptotal = PA + PB + PC + …

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15
Q

What is the mole fraction of a gas?

A

The ratio of moles of a particular gas to the total number of moles of all gases present

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16
Q

What is the relationship between mole fraction and partial pressure?

A

Partial pressure = mole fraction × total pressure

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17
Q

What happens to the equilibrium position when water is added to an equilibrium mixture?

A

There is no effect, as water dilutes all ions equally

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18
Q

What does the equilibrium constant Kp represent?

A

The equilibrium constant in terms of partial pressures for gaseous reactions

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19
Q

How are equilibrium expressions involving partial pressures written?

A

Similar to those involving concentrations, but with pressures instead

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20
Q

What happens to the equilibrium position when the concentration of a reactant decreases?

A

Equilibrium shifts to the left

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21
Q

In equilibrium calculations, what information is typically needed?

A

Number of moles of reactants and products at equilibrium and the volume of the reaction mixture

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22
Q

What is the effect of increasing temperature on an exothermic reaction?

A

Equilibrium moves in the endothermic direction to reverse the change

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23
Q

What is the significance of solids in equilibrium expressions?

A

Solids are ignored in equilibrium expressions

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24
Q

What is the formula for the equilibrium constant Kc?

A

Kc is specific and only changes with temperature

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25
What is the effect of decreasing pressure on a gaseous reaction?
Equilibrium shifts in the direction that produces a larger number of gas molecules
26
What are the roles of the reactants and products at equilibrium?
The roles of each of the reactants and products at equilibrium together with the volume of the reaction mixture
27
How are concentrations of reactants and products calculated?
Concentrations can be calculated from the number of moles and total volume
28
Given the reaction CH3COOH (l) + C2H5OH (l) ⇌ CH3COOC2H5 (l) + H2O (l), what are the equilibrium concentrations?
0.470 mol dm-3 for CH3COOH, 0.070 mol dm-3 for C2H5OH, 0.364 mol dm-3 for CH3COOC2H5, 0.364 mol dm-3 for H2O
29
What is the equilibrium constant expression for the reaction CH3COOH (l) + C2H5OH (l) ⇌ CH3COOC2H5 (l) + H2O (l)?
Kc = [H2O][CH3COOC2H5] / [C2H5OH][CH3COOH]
30
Calculate Kc for the reaction CH3COOH (l) + C2H5OH (l) ⇌ CH3COOC2H5 (l) + H2O (l) using the given concentrations.
Kc = 4.03
31
What is the significance of significant figures in reporting Kc?
The final answer should be given to the smallest number of significant figures used in the question
32
What is an ICE table?
An Initial, Change, and Equilibrium table used to determine equilibrium concentrations
33
In the hydrolysis of ethyl ethanoate, what is the initial amount of ethyl ethanoate and water?
0.1000 mol each
34
What is the equilibrium concentration of water in the hydrolysis of ethyl ethanoate?
0.0654 mol dm-3
35
Calculate Kc for the hydrolysis of ethyl ethanoate given the equilibrium concentrations.
Kc = 0.28
36
What does Kp represent in equilibrium expressions?
Kp represents the equilibrium constant in terms of partial pressures
37
Calculate Kp for the reaction 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) with given partial pressures.
Kp = 9.1 x 10–6
38
How do you calculate partial pressures from mole fractions?
Partial pressures are calculated by multiplying mole fractions by total pressure
39
What is the total pressure in the reaction H2 (g) + I2 (g) ⇌ 2HI (g)?
100 kPa
40
What is the equilibrium partial pressure of C in the reaction A (g) + B (g) ⇌ 2C (g) with a total pressure of 3 atm?
2 atm
41
Does changing concentration affect Kc?
No, Kc is not affected by changes in concentration
42
What happens to Kc when temperature is increased in an endothermic reaction?
Kc increases
43
What happens to Kc when temperature is increased in an exothermic reaction?
Kc decreases
44
Does the presence of a catalyst affect Kc?
No, a catalyst does not affect Kc
45
What is the effect of a catalyst on the rate of reaching equilibrium?
A catalyst increases the rate at which equilibrium is reached
46
What factors affect the value of Kc?
Only a change in temperature affects the value of Kc
47
What will increase the value of Kp for the reaction 2A (g) + B (g) ⇌ 2C (g)?
An increase in temperature
48
What is the effect of temperature changes on the value of Kp?
Only temperature changes permanently affect the value of Kp
49
How does an increase in temperature affect the reaction shift in equilibrium?
An increase in temperature shifts the reaction in favour of the products
50
What happens to the concentrations of products and reactants when the equilibrium shifts to the right?
The [products] increases and [reactants] decreases, therefore, the Kp value increases
51
What is the Haber process used for?
The Haber process involves the synthesis of ammonia
52
What is the balanced equation for the Haber process?
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
53
What is the ΔHr value for the Haber process?
ΔHr = -92 kJ mol-1
54
How does pressure affect the yield of ammonia in the Haber process?
An increase in pressure will result in the equilibrium shifting in the direction of the fewest molecules of gas formed
55
What compromise pressure is chosen in the Haber process?
200 atm
56
What is the compromise temperature used in the Haber process?
400-450 °C
57
How is ammonia removed in the Haber process?
Removing ammonia by condensing it to a liquid causes the equilibrium position to shift to the right
58
What catalyst is used in the Haber process?
Iron catalyst
59
What is the Contact process used for?
The Contact process involves the synthesis of sulfuric acid
60
What is the balanced equation for the Contact process?
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
61
What is the ΔHr value for the Contact process?
ΔHr = -197 kJ mol-1
62
What compromise pressure is typically used in the Contact process?
1 atm
63
How is SO3 removed in the Contact process?
SO3 is removed by absorbing it in 98% sulfuric acid
64
What catalyst is used in the Contact process?
Vanadium(V) oxide
65
Define an acid.
An acid is a substance that neutralises a base forming a salt and water.
66
What happens when an acid dissolves in water?
Acids release hydrogen ions when they dissolve in water.
67
What is the formula for hydrochloric acid?
HCl
68
What ions are formed when hydrochloric acid dissociates in water?
H+ + Cl–
69
What is a monoprotic acid?
A monoprotic acid is an acid that fully dissociates into its ions.
70
Give an example of a weak acid.
Ethanoic acid (CH3COOH)
71
Define a base.
A base is a compound that neutralises an acid forming a salt and water.
72
What is an alkali?
A base that is soluble in water.
73
What is the Brønsted-Lowry Theory?
The Brønsted-Lowry Theory defines acids and bases in terms of proton transfer.
74
What is a Brønsted-Lowry acid?
A species that gives away a proton (H+).
75
What is a Brønsted-Lowry base?
A species that accepts a proton (H+) using its lone pair of electrons.
76
What are amphoteric species?
Species that can act both as acids and bases.
77
What defines a strong acid?
A strong acid dissociates almost completely in aqueous solutions.
78
What is an example of a strong acid?
HCl, HNO3, H2SO4
79
What defines a weak acid?
A weak acid partially dissociates in aqueous solutions.
80
How is the pH calculated for a strong acid?
pH = -log10 [H+ (aq)]
81
What is the pH range for acids?
Below 7
82
What is the pH range for alkalis?
Above 7
83
What is the equilibrium constant expression for the dissociation of water?
Kc = [H+][OH-]/[H2O]
84
What is a strong base?
A strong base dissociates almost completely in aqueous solutions.
85
Give an example of a weak base.
NH3 (ammonia)
86
What is the equilibrium constant expression for the reaction 2O (l) ⇌ H+ (aq) + OH– (aq)?
Kc = [H+][OH–] / [H2O] ## Footnote Kc can be rearranged to Kc x [H2O] = [H+][OH–]
87
What does Kw represent in the context of water at 298K?
Kw = [H+][OH–] = 10^-14 mol² dm^-6 ## Footnote Kw is the ionic product of water.
88
At 298K, what are the concentrations of OH- and H+ ions in pure water?
10^-7 mol dm^-3 ## Footnote Pure water is neutral with equal concentrations of OH- and H+.
89
What is the formula to calculate the pH of a solution?
pH = –log [H+ (aq)] ## Footnote [H+ (aq)] is the concentration of H+ / H3O+ ions.
90
What is the pH of pure water at 298K?
7
91
What is the relationship between H+ and OH- ions in acidic solutions?
H+ > OH- ## Footnote pH of acidic solutions is always below 7.
92
What is the relationship between H+ and OH- ions in basic solutions?
OH- > H+ ## Footnote pH of basic solutions is always above 7.
93
How can strong and weak acids be distinguished?
By their: * pH value * Electrical conductivity * Reactivity
94
What is the dissociation equation for an acid HA in solution?
HA → H+ + A-
95
What is the pH of a 0.1 mol dm-3 HCl solution?
1
96
What is the pH of a 0.1 mol dm-3 CH3COOH solution?
2.9
97
What is the most accurate method to determine pH?
Using a pH meter
98
What is a less accurate method for measuring pH?
Using universal indicator paper
99
What does a stronger acid indicate in terms of electrical conductivity?
Higher electrical conductivity ## Footnote Stronger acids have a greater concentration of H+ ions.
100
What occurs during a neutralization reaction?
An acid and a base react to form water and a salt.
101
What is the general equation for a neutralization reaction?
Acid + base (alkali) → salt + water
102
What ions are considered spectator ions in a neutralization reaction?
Na+ (aq) + Cl– (aq)
103
What is produced when an acid reacts with a metal carbonate?
Salt + water + carbon dioxide
104
What are pH titration curves used for?
To determine the concentration of an unknown solution in neutralization reactions.
105
What is the equivalence point in a titration?
The point at which an equal number of moles of titrant and analyte react.
106
How do you sketch a pH titration curve?
Draw axes with volume added on the x-axis and pH on the y-axis.
107
What is the initial pH of a strong acid in a titration?
About 1 or 2
108
What is the initial pH of a weak acid in a titration?
About 2-3
109
What happens at the equivalence point of a strong acid + strong alkali titration?
The pH is 7
110
What is the pH at the equivalence point of a strong acid + weak alkali titration?
About 5.5
111
What is the pH at the equivalence point of a weak acid + strong alkali titration?
About 9
112
What characterizes the pH titration curve of a weak acid + weak alkali?
There is no vertical region; only a point of inflexion at the equivalence point.
113
What is the final pH of a strong acid + strong alkali titration after excess alkali is added?
About 13-14
114
What is the volume calculated in cm3 for the given expression?
15.0 cm3 ## Footnote The calculation is based on the formula provided.
115
What must the equivalence point be above for a weak acid - strong base titration?
pH 7
116
What is the maximum pH value given in the question?
12.5
117
What is the maximum volume of base added given in the question?
20 cm3
118
What are indicators?
Substances that change colour when added to acidic or alkaline solutions
119
Why is the pH of the equivalence point important when choosing an appropriate indicator?
Because it determines which indicator will show a colour change at the endpoint
120
What are the two most common indicators used in titrations?
* Methyl orange * Phenolphthalein
121
What is the pH range for methyl orange?
3.1 - 4.4
122
What is the pH range for phenolphthalein?
8.3 - 10.0
123
What colour change does methyl orange undergo?
Red to yellow
124
What colour change does phenolphthalein undergo?
Colourless to pink
125
In a strong acid and strong alkali titration, which indicators can be used?
* Methyl orange * Phenolphthalein
126
In a strong acid and weak alkali titration, which indicator can be used?
Methyl orange
127
In a weak acid and strong alkali titration, which indicator is appropriate?
Phenolphthalein
128
In a weak acid and weak alkali titration, what should be considered instead of indicators?
A different method
129
True or False: Both methyl orange and phenolphthalein can be used in a weak acid and weak alkali titration.
False
130
Fill in the blank: The pH range at which methyl orange changes colour falls ______ the curve in a weak acid and strong alkali titration.
below

Chemistry AS (9 decks)

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