Unit 1 Inorganic Chemistry: Key Area 4 - Chemical Equilibrium Flashcards
(128 cards)
1
Q
what are the 3 factors that affect equilibrium?
A
1) Concentration
2) Temperature
3) Pressure (only applies to gaseous substances)
2
Q
In the reaction A + B ⇌ C + D what happens to equilibrium if you add more A or B (reactant)?
A
Shifts to right
3
Q
In the reaction A + B ⇌ C + D what happens to equilibrium if you remove more C or D (product)?
A
Shifts to right
4
Q
In the reaction A + B ⇌ C + D what happens to equilibrium if you add C or D (product)?
A
Shifts to left
5
Q
In the reaction A + B ⇌ C + D what happens to equilibrium if you remove A or B (reactant
A
Shifts to left
6
Q
In the reaction A + B ⇌ C + D ΔH = -ve what happens to equilibrium if you increase temperature?
A
Favours the endothermic reaction.
7
Q
In the reaction A + B ⇌ C + D ΔH = -ve what happens to equilibrium if you decrease temperature?
A
Favours the exothermic reaction.
8
Q
In the reaction A(g) + B(g) ⇌ C(g) + D(g) what happens to equilibrium if you increase pressure?
A
Shift to side which has less gaseous moles.
9
Q
In the reaction A(g) + B(g) ⇌ C(g) + D(g) what happens to equilibrium if you decrease pressure?
A
Shift to side with more gaseous moles.
10
Q
What are the 2 types of equilibrium?
A
Homogeneous and Hetrogeneous.
11
Q
What happens in Homogeneous equilibrium?
A
Reactants and products are in the same physical state.
12
Q
What happens in Hetrogeneous equilibrium?
A
Reactants and products are in different physical states.
13
Q
What does the value of an equilibrium constant indicate?
A
The position of equilibrium.
14
Q
What are factors that affect equilibrium constant?
A
K is dependent on temperature and independent of concentration and pressure.
15
Q
In the reaction A + B ⇌ C + D ΔH = -ve how does a rise in temperature affect K?
A
It will shift the equilibrium to the left, decreasing the quantity of products and increasing the quantity of reactants. Which will cause a decrease in K.
16
Q
In the reaction A + B ⇌ C + D ΔH = +ve how does a rise in temperature affect K?
A
It will shift the equilibrium to the right, increasing the quantity of products and decreasing the quantity of reactants. Which will cause an increase in K.
17
Q
How does concentration affect the equilibrium position and the value of K?
A
Equilibrium position - Changes
Value of K - No Change
18
Q
How does temperature affect the equilibrium position and the value of K?
A
Equilibrium position - Changes
Value of K - Changes
19
Q
How does pressure affect the equilibrium position and the value of K?
A
Equilibrium position - Changes
Value of K - No Change
20
Q
How does catalyst affect the equilibrium position and the value of K?
A
Equilibrium position - No Change
Value of K - No Change
21
Q
What are liquids that do not mix said to be?
A
Immiscible
22
Q
What does dissolving a solute in 2 immiscible liquids allow the solute to do?
A
Distribute itself between the 2 liquids.
23
Q
What is a H+ ion?
A
Proton
24
Q
What happens to the H+ ion in water?
A
As it cannot exist on its own, it is attracted to the polar water molecules. It becomes a hydrated proton known as a hydronium ion (H3O+) and the H+ ion and water molecule form a dative covalent bond.
25
How can the ionisation of water be represented?
H2O(l) H2O(l) ⇌ H3O+(aq) + OH−(aq)
26
What is a hydronium atom?
A hydrated proton H3O+(aq).
27
What is a shortened version of H3O+(aq)?
H+
28
What is the K value of pure water?
1
29
As pure water has a value of K what is the equation of K for pure water?
K = [H3O+] [OH−] or K = [H+] [OH−]
30
What is the equilibrium constant Kw known as?
The ionic product of water.
31
What is water in terms of K and what does this mean?
Water is amphoteric meaning it can act as both an acid and a base.
32
At 25°C what is the approximate value of K?
1x10(14)
33
How do higher temperatures affect the pH of water?
They do not become more acidic.
34
In water and aqueous solutions with a pH value of 7 and temperature of 25°C what are the concentrations of H3O+(aq) and OH−(aq)?
Both x 10(-7) mol/l.
35
If the concentration of H3O+(aq) or the concentration of
| OH−(aq) is known, how can the concentration of the other ion can be calculated?
Using Kw or by usH + pOH = 14.
36
When is a solution said to be acidic?
When there is an excess of hydrogen ions over hydroxide ions (i.e. pH < pOH).
37
In the case of water what is the concentration of always the same?
The concentration of hydrogen ions and hydroxide ions.
38
What still stays the same in water even if the pH of the water changes?
The water stays neutral (pH =pOH).
39
What type of scale is a pH scale?
A logarithmic scale
40
What does a change in pH by 1 unit change the concentration of H+ by?
10
41
What does a change in pH by 2 units change the concentration of H+ by?
100
42
What is the value of pH +pOH?
14
43
What does the Arrhenius definition of acids and bases only apply to?
Aqueous solutions
44
What is the Arrhenius definition of what happens to an acid when it is dissolved in water?
An acid dissociates to increase H+ ions when dissolved in water e.g. [H+] > [OH-]. (Acids produce H+ ions in aqueous solution).
45
What is the Arrhenius definition of what happens to a base when it is dissolved in water?
A base dissociates to increase OH- ions when dissolved in water e.g. [OH-] > [H+]. (Bases produce OH− ions in aqueous solution).
46
What are problems with the Arrhenius definition of how acids and bases dissolve in water?
- Why substances, such as NH3 and Na2CO3, dissolve in water to form basic solutions, even though they do not contain OH– ions.
- Why substances, such as CO2, dissolve in water to form acidic solutions, even though they do not contain H+ ions.
- That acid–base reactions take place outside aqueous solution.
47
What is the Brønsted Lowry definition of acids and bases?
The Brønsted-Lowry definitions of acids and bases state that an acid is a proton donor and a base is a proton acceptor. (does not need to have OH-) Base structure must contain an atom with an unshared pair of electrons.
48
For the equation HCL(aq) + H2O(l) ⇌ H3O+(aq) +Cl-(aq) what happens according to the Brønsted Lowry theory?
- HCL donates a proton to water therefore HCL is an acid.
| - H2O accepts a proton from HCL therefore H2O is a base.
49
What happens in a Brønsted Lowry acid-base reaction?
- The original base becomes an acid in the reverse reaction.
| - The original acid becomes a base in the reverse process.
50
For every acid what is there?
For every acid there is a conjugate base, formed by the loss of a proton.
51
What is the general equation for a conjugate acid reaction?
HA (acid) ⇌ H+ + A-(conjugate base)
52
What is the general equation for a conjugate acid reaction H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)?
H2O(l)(acid) + H2O(l) ⇌ H3O+(aq) + OH-(aq)(conjugate base)
53
What is the general equation for a conjugate acid reaction of HCL(aq) + H20(l) ⇌ H30+(aq) + Cl-(aq)?
HCL(aq)(acid) + H20(l) ⇌ H30+(aq) + Cl-(aq)(conjugate base)
54
For every base what is there?
A conjugate acid which is formed by the gain of a proton.
55
What is the general equation for a conjugate base reaction of NH3 + H2O ⇌ NH4+ + OH-?
NH3(base) + H2O ⇌ NH4+(conjugate acid) + OH-
56
What is the general equation for a conjugate acid reaction of CO3^2-(aq) + H3O+(aq) ⇌ HCO3^-(aq) +H2O(l)?
CO3^2-(aq)(base) + H3O+(aq) ⇌ HCO3^-(aq) +H2O(l)(conjugate acid)
57
What is the general equation for a conjugate acid and base reaction of OH+(aq) + H3O+ (aq) ⇌ H2O(l) + H2O(l)?
OH+(aq)(base) + H3O+(aq)(acid) ⇌ H2O(l)(conjugate acid) + H2O(l)(conjugate base)
58
What do conjugate acid-base pairs differ by?
Only one proton
59
What can amphoteric substances act as?
Either an acid or a base because they have both a transferable H and an atom with lone pair electrons. As water can act as a base, accepting H+ from HCL and as an acid by donating H+ to NH3.
60
What are acids either?
Acids are either strong or weak depending on wether or how they (dissociate) dissolve in water.
61
How do strong acids dissociate into ions in solution?
Strong acids are completely dissociated into ions in aqueous solution.
62
What is an example of a strong acid reaction and what would be the [H+] concentration if the HCL concentration is 0.1 mol/l?
HCL(aq) + H20(l) ⇌ H30+(aq) + Cl-(aq)
| [H+] concentration is 0.1 mol/l
63
What are examples of strong acids?
- Hydrochloric acid (HCL)
- Nitric acid (HNO3)
- Sulphuric acid (H2SO4)
64
How do weak acids dissociate into ions in solution?
Weak acids do not completely dissociate into ions in solution.
65
What is an example of a weak acid reaction and why is this?
CH3COOH(aq) ⇌ CH3COO-(aq) + H20+(aq)
| - Ethanoic acid solutions contain molecules of CH3COOH as well as H3O+ and CH3COO- ions.
66
What are examples of weak acids and where can more examples be found?
- Ethanoic acid (CH3COOH)
- Methanoic acid (HCOOH)
- Sulphurous acid (H2SO3)
- Carbonic acid (H2CO3)
- Pg 13 in the databook
67
What does the type of solvent effect?
The acid properties
68
What is an example of a solvent that affects acidic properties?
HCL in non - polar solvents - no dissociation therefore only HCL molecules no ions, so it is not an acid.
69
How do strong bases/alkalis dissolve?
By completely dissociating into ions.
70
How do weak bases/alkalis?
Do not completely dissociate into ions in solution.
71
Strong acid vs weak acid?
Higher conductivity, lower pH, faster reaction due to higher H+ ion concentration.
72
Strong base/alkali vs weak base/alkali?
Higher conductivity, higher pH due to higher OH- ion concentration.
73
What do equimolar solutions of strong and weak acdis and alaklis differ in?
Concentration, pH and speed of reaction. This is due to the different concentration of H+ and OH- ions in solution.
74
How do strong bases/alkalis dissolve?
By completely dissociating into ions.
75
What is an example of a strong base/alkali reaction?
NaOH(s) + (aq) ⇌ Na+(aq) + OH-(aq)
76
What are examples of strong base/alkalis?
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Lithium hydroxide (LiOH)
77
How do weak bases/alaklis dissolve?
They do not completely dissociate into ions in solution.
78
What is an example of a weak base/alkali reaction and why?
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
| Ammonia solutions contain molecules of NH3 as well as NH4+ and OH- ions.
79
What are examples of weak bases /alkalis
- Aminomethane (CH3NH2)
- Ammonia (NH3)
- Aminoethane (C2H5NH2)
80
what does the pH of a salt solution depend on?
The strength of the acid and base from which it was formed.
81
What is the pH of a salt of a strong acid and weak base?
Acidic
82
What is the pH of a salt of a strong acid and strong base?
Neutral
83
What is the pH of a salt of a strong acid and weak base?
Alkaline
84
What are all salts?
All salts are strong electrolytes and completely ionise in solution.
85
What will happen to the ions of a weak acid or base when dissolved?
They will set up an equilibrium with the ions in water.
86
What happens in terms of equilibrium in the acidic salt reaction of Ammonium chloride with water?
Ammonium chloride completely dissociates. The ammonium ions form an equilibrium with the OH- ions moving the water equilibrium to the right. Excess H+ are formed so pH is less than 7.
87
What happens in terms of equilibrium in the alkaline salt reaction of Sodium Ethanoate with water?
Sodium ethanoate completely dissociates. The ethanoate ions form an equilibrium with the H+ ions moving the water equilibrium to the right. Excess OH- ions are formed so the pH is greater than 7.
88
What is a soap?
Soap is a salt formed between a fatty acid (weak acid) and sodium or potassium hydroxide. Therefore soaps are alkaline.
89
When a weak acid is dissolved in water what is the general dissociation?
HA ⇌ H+ + A-
90
What is Ka known as?
The acid dissociation constant.
91
What is the equation for the acid dissociation?
Ka = ([H3O+] [A-]) / [HA] or pKa = -log10 Ka
92
What does a smaller value of Ka represent?
A weaker acid
93
When is the equation for amending Ka to find out [H+] of the dissociation of a weak acid?
H+ = √Ka x C where C is the concentration of the acid.
94
What does pKa represent?
The dissociation constant of an acid.
95
How can the value of pKa be found?
pKa = -log10 Ka
96
Where are the Ka values found?
Pg 13 on the data book
97
What does an increase in Ka represent and how does this affect the value of pKa?
As Ka increases (acid strength increases) and pKa decreases (due to the pKa equation above).
98
What is the equation for the pH value of a weak acid?
pH = 1/2 pKa - 1/2 log10c
99
What is the equation for diluting an acid?
pH = -log10 [H+]
100
What is the pH of 0.1 mol l-1 of a strong acid?
pH = -log10(0.1) = 1
101
What is the pH of 0.01 mol l-1 of a strong acid?
pH = -log10(0.01) = 2
102
How will a dilution of a strong acid by a factor of 10 affect the pH of the acid?
Change the pH of the acid by 1 unit.
103
What is the pH of 0.1 mol l-1 of a weak acid?
pH = 1/2 pKa - 1/2 log(0.1) = 0.5
104
What is the pH of 0.01 mol l-1 of a weak acid?
pH = 1/2 pKa - 1/2 log(0.01) = 0.
105
How will a dilution of a strong acid by a factor of 10 affect the pH of the acid?
Change the pH of the acid by 0.5 units.
106
What is a buffer solution?
A buffer solution is one in which the pH remains approximately constant when small amounts of acid, base or water are added.
107
What are the 2 types of buffers?
Basic and acidic
108
What are common examples of buffers?
Blood, Swimming pool, Contact lens solution.
109
What does an acid buffer consist of?
An acid buffer consists of a solution of a WEAK acid and one of its SALTS.
110
What can a weak acid supply to an acid buffer?
The weak acid can supply additional hydrogen ions when these are removed by the addition of a small amount of base.
111
What can the salt of a weak acid provide to an acid buffer?
The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions produced by the addition of small amounts of acid.
112
What does a basic buffer consist of?
A solution of a weak base and one of its salts.
113
What does a weak base provide in a basic buffer?
Remove excess added hydrogen ions.
114
What does the salt of the base provide in a basic buffer?
The conjugate acid to replace hydrogen ions removed.
115
What is the equation for the pH of a buffer solution?
pH = pKa - log10[acid/salt]
116
What are indicators?
Indicators are weak acids that change colour when they are converted into their conjugate base.
117
How can the dissociation of indicators be represented and what is the calculation for the dissociation constant for the indicator?
Hln(aq) + H2O(l) ⇌ H3O+(aq) + ln-(aq)
Kln = ([H3O+] [ln-]) / [Hln]
Where :
In- = indicator
Hln = conjugate base
And In- and HIn have different colours
118
In an aqueous solution what is distinctively different between the acid indicator and that of its conjugate base?
Colour
119
What is the colour of an indicator determined by?
The colour of the indicator is determined by the ratio of [HIn] to [In-].
120
What is the theoretical point at which a colour change occurs in an indicator?
The theoretical point at which colour change occurs is when [H3O+] = KIn.
121
When is the colour change said to be distinguishable in an indicator?
when [HIn] and [In-] differ by a factor of 10.
122
How can the pH range over which a colour change occurs be estimated by the expression:
pHpKIn 1
pH = pKIn (+/-) 1
123
What is the equivalence point?
When the reaction is just completed.
124
For a titration between a strong acid and a strong base what will the equivalence point be?
pH 7
125
If titrating with a base, what should you ideally choose the indicator to be?
An indicator that has a pKIn 1 less than the pH at the equivalence point.
126
If titrating with an acid, what should you ideally choose the indicator to be?
An indicator that has a pKIn 1 more than the pH at the equivalence point.
127
What will the equivalence point be for a weaker acid?
Higher as the change in pH becomes less dramatic.
128
What does the pH have to be at least for the indicator to work?
2
