Chemical Equilibrium Flashcards
1
Q
When is a reaction equilibrium
A
When the concentrations of reactants and products are constant
2
Q
What’s the equilibrium constant
A
Has the symbol K
3
Q
What does the value of the equilibrium constant give
A
Indicates the position of equilibrium
4
Q
What does the numerical value of equilibrium constant depend on
A
The reaction temperature and is independent of concentration and/or pressure
5
Q
What happens to K in endothermic reactions
A
A rise in temperature causes in increase in K and yield is increased
6
Q
What happens to K in Exothermic reactions
A
A rise in temperature causes a decrease in K and yield of product is decreased
7
Q
What does a catalyst do to equilibrium constant
A
Does not affect the value of the equilibrium constant
8
Q
What’s dynamic equilibrium
A
Is when the rates of two opposing processes become equal
9
Q
What’s a closed system
A
Has no exchange of matter or energy with its surroundings, must be the case for equilibrium to take place
10
Q
In equilibrium what is the rate of the forward reaction equal to
A
The rate of the reverse reaction
11
Q
What is le chateliers principle
A
If a system is at equilibrium and a change is made in any of the conditions then the system responds to counteract the change as much as possible
12
Q
What does a catalyst do to equilibrium
A
Speeds up the rate at which equilibrium is achieve but has no effect on the position
13
Q
What does increasing the concentration of reactants do
A
Moves equilibrium to the right
14
Q
What does increasing concentration of products do
A
Moves equilibrium to the left
15
Q
What does increasing temperature do
A
Equilibrium shifts direction to the endothermic side
16
Q
What does decreasing temperature do
A
Equilibrium shifts to direction of Exothermic reaction
17
Q
What’s the equilibrium constant formula
A
aA +bB - cC +dD k=[C]c[D]d/ [A]a[B]b
18
Q
What’s homogeneous equilibrium
A
All the species are in the same gaseous phase
19
Q
What’s heterogeneous equilibrium
A
The species are in more than one phase
20
Q
What’s the value given to pure solids or liquids acting as solvents in equilibrium reaction
A
1
21
Q
What are equilibrium constants independent of
A
Concentrations or partial pressures of species in any given reaction
22
Q
What’s the ratio of reactants and products when there is a low and high value of K
A
High K-more product
Low K-more reactant
23
Q
Where does equilibrium lie when k is bigger, less and equal to one
A
Bigger lies more to the right
Less lies more to the left
Equal favours neither reactants or products
24
Q
What does knowing the value of constant allow us to do
A
-Determine the direction in which a reaction will proceed to achieve equilibrium
-The ratio of the concentrations of reactants and products when equilibrium is reached
25
What happens to K at high and low temperatures
At high temps products are favoured so K increases
At low temps reactants are favoured so K decreases
26
What does a catalyst do to equilibrium
Speeds up the rates of the forward and reverse reactions by an alternative reaction pathway with lower activation energy
27
What’s the Brønsted-Lowry definition
States that an acid is a proton donor and a base is a proton acceptor
28
What is there for every acid and base
For every acid there is a conjugate base formed by the loss of a proton
For every base there is a conjugate acid formed by the gain of a proton
29
In water and aqueous solutions what is there an equilibrium between
Water molecules and hydronium and hydroxide ions
30
What is the equation for the equilibrium in water and aqueous solutions
H2O(l) + H2O(l) <=> H3O+(aq) + OH-(aq)
31
How can water be described
As amphoteric and can act as an acid or base
32
What is Kw
The dissociation constant for the ionisation of water and known as the ionic product
33
What is the value of Kw
Varies with temperature and at 25 degrees it is 1x10 to the -14
34
What is the relationship between ph and hydrogen ion concentration given by
pH= -log10[H3O+]
And [H3O+]= 10 the the -ph
35
In water and aqueous solutions with a ph of 7 the conc of H3O+ and OH- is what
10 to the -7 at 25 degrees
36
How to calculate the concentration of the other ion if either H3O+ or OH- is known
Calculate Kw using
pH+pOH=14
37
What are hydronium ions
H+ ions
38
Describe an acid
Proton donor and when it donates the species left is called a conjugate base
39
Describe a base
Proton acceptor and when it accepts a proton the species formed is a conjugate acid
40
What’s the ionic product
The dissociation constant for the ionisation of water, Kw
41
What is the Kw formula
Kw=[H3O+(aq)][OH-(aq)]
42
What is the ph scale
Gives a measure of the concentration of hydrogen ions in am aqueous solution
43
How can the ph of any aqueous solution be calculated
pH= -log10[H3O+] and [H3O+] = 10 to the -pH
44
What is the ph scale and what does it mean
A logarithmic scale meaning any change in pH unit requires a factor of 10 change in the hydrogen ion concentration
45
What do strong acids and bases do
Fully dissociate in water to ions
46
What do weak acids and bases do
Only dissociate partially in water to ions
47
What are examples of strong acids and bases
Acids- nitric, sulfuric and hydrochloric acid
Base-sodium and potassium hydroxide
48
What are examples of weak acid and bases
Acids- ethanoic, carbonic and sulfurous acid
Base- ammonia and amines
49
What’s the formula for finding the pH of strong acids and bases
pH＝-log10[H＋]
50
What’s a monoprotic or mono basic acid
Any weak or strong acid which is capable of donating only one hydrogen ion per molecule
51
What’s a diprotic or dibasic acid
An acid hitch can donate two hydrogen ions per molecule
52
What is the degree of ionisation definition
The ability of the non-ionised acid molecule to produce hydrogen ions
53
When do acids tend to be stronger
The more the acid can produce hydrogen ions.
Tend to be lab acids
They fully dissociate in water meaning there is a one way arrow in the equation
54
What happens when water is added to an acid
Strength is not related to the concentration of the acid. More water will produce a more dilute acid but will not alter the strength of the acid
55
Where do you find weak acids
In equilibrium mixtures of non ionised acid molecules, hydrogen ions and the conjugate base of the acid
56
What are examples of weak acids
Most carboxylic acids, ethanoic acid
57
Describe ethanoic acid
The acidic hydrogen atom is the one bonding to the oxygen atom, only some of the ethanoic acid molecules dissociate into ions, it’s a weak monoprotic acid
58
What is classified as a base
Any substance that reacts with an acid and accepts the proton from the acid
59
What is a soluble base called
Alkali as it will produce hydroxide ions when in an aqueous solution
60
What is the rule between alkali and bases
All alkalis are bases but not all bases are alkali
61
What is a strong base and examples
A string base dissociates completely in aqueous solution. Strong bases are typically group 1 metal hydroxides e.g sodium hydroxide
62
What are weak bases and examples
Weak bases only partially dissociate in aqueous solutions. Ammonia and amino alkanes are examples
63
How do you tell the difference between weak and strong acid and bases by an equation
Weak have equilibrium arrow (two)
Strong only have one arrow in the equation
64
For acids and bases that ionise fully what can be determined
The H+ or OH- can be determined from the initial concentration of the acid or base
65
What’s the formula for strong acids
PH= -log10[H+]
[H+]=10 to the -ph
66
What’s the formula for strong bases
Kw=[H+][OH-]
67
What’s the acid dissociation constant formula
Ka= [products]/[reactants]=[H+][A-]/[HA] or by pKa=-log10Ka
68
How is the approximate pH of a weak acid found
pH= 1/2pKa - 1/2log10c
69
Describe equimolar solutions of weak and strong acids or bases
Have different pH values, conductivity and reaction rates, but the stoichiometry of reactions are the same
70
How is a neutral solution formed from a soluble salt
A soluble salt of a strong parent acid or strong parent base dissolves in water
71
How is an alkaline solution formed from a soluble salt
A soluble salt of a weak parent acid a strong parent base dissolves in water
72
How is an acidic solution formed from a soluble salt
A soluble salt of a strong parent acid and a weak parent base dissolves in water to produce an acidic solution
73
What is the equation formula for acid dissociation constant
HA(aq) equilibrium arrows H3O+ (aq) + A- (aq) use this to put into the formula Ka=[H+][A-]/ [HA]
74
What is the symbol c in acid dissociation constant
The original acid concentration which is [HA]
75
Describe ammonia
Weak base and is polar covalent gas molecule that dissolves readily in water a small amount of its molecules reacts with water to produce hydroxide ions
76
What happens the weaker the base is
The weaker the base is the stronger the conjugate acid that will be formed with a higher Ka value in other words the conjugate acid of a weak base is a strong acid
77
What do strong acids with greater dissociation have
Greater concentration of hydrogen ions and so have a lower ph and Greater conductivity
78
Compare weak and strong bases
Weak bases produce fewer OH- ions and therefore less alkaline than strong bases of equal concentration. Weak bases have a lower ph and therefore conductivity
79
What does the pH of a salt solution depend on
The strength of the parent acid and parent base from which it was formed
80
What are all salts
All salts are strong electrolytes and dissociate completely in solution
81
What is the ph of a solution of a salt of a weak acid and a strong base
Ph greater than 7
82
What is the ph of a solution of a salt of a strong acid and weak base
Ph less than 7
83
What is a buffer solution
A buffer solution is one in which the pH remains approximately constant when small amounts of acid or base are added
84
What does an acid buffer consist of
Consists of a solution of a weak acid and one of its salts
85
What does a basic buffer consist of
Consists of a solution of a weak base and one of it’s salts
86
How can the required composition of an acid buffer solution be calculated
From the desired ph and the acid dissociation constant
87
What’s the formula for calculating the approximate ph of an acid buffer solution
pH= pKa-log10 x [acid]/[salt]
88
What are indicators
Weak acids and represented as Hln (aq) + H2O (l) ea H3O+ (aq) + ln- (aq)
89
In an aqueous solution what is the colour of the acid
The colour of the acid is distinctly different from that of it’s conjugate base
90
How is the colour of an indicator determined
The ratio of [Hln] to [ln-]
91
What is the theoretical point at which colour change occurs
[H3O+]=Kln
92
When is colour change distinguishable
When [Hln] and [ln-] differ by a factor of 10
93
What’s the pH range over which colour change occurs
Estimated by pH=pKln + or - 1
94
How are buffer solutions defined
As solutions that resist the change in pH, remain constant on adding small amounts of acid or base or by diluting the solution with water
95
What are uses if bufffers
Skin creams
96
What are the two types of buffers
Acid buffers and basic buffers
97
What’s an acid buffer
The solution contains a mixture of weak acid and its conjugate base the ph is lower than 7
98
Whats a basic buffer
A solution that contains a mixture of a weak base and its conjugate acid the ph id higher than 7
99
What equation represents a buffer
The equilibrium equation, HA ea H+ = A-
HA is the acid
H+ is the conjugate acid
A- is the conjugate base
100
What must a buffer do to stabilise the ph of a solution
Must be able to react with added OH and H ions
101
Learn how to do all k calculations
102
What are indicators
Are weak acids or bases that are able to give a measure of the pH of a solution by their colour represented as Hln (aq) + H2O+ ea H3O+ + Ln- (aq)
103
What must be considered when deciding which indicator to use in a trait ration
The equivalence point
104
What is the equivalence point
Is the point in a titration where the amount of titration added is enough to neutralise the analyse solution completely
105
What indicates the type of titration
The shape of the curve, the vertical region of the curve shows where there is a rapid change in ph and shows the equivalent point
106
How do you figure out a suitable indicator
For a strong acid strong base titration between ph 3 to 10
Weak acid strong base ph 7 to 10
Strong acid weak base ph 3 to 8
Weak acid weak base need a ph meter to produce a titration curve
107
What does the equivalence point depend on
The strength of the acid and base used and the nature of the alt formed at the end point
108
What does the indicator colour during a titration depend on
The concentration of non ionised indicator molecules [Hln] and the conjugate base molecules [ln-]
109
What indicator is suitable for a weak acid weak base titration
No suitable indicator
