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Chemistry (Year 12) > Unit 3: Topic 1 > Flashcards

Unit 3: Topic 1 Flashcards

(102 cards)

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1
Q

Reactions that can only occur in the forwards direction are called…

A

Irreversible reactions

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2
Q

Define equilibrium.

A

Equilibrium occurs when the rate of the forwards and reverse reactions are equal.

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3
Q

What does the position of equilibrium describe?

A

The ratio of reactants to products

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4
Q

Why are some chemical reactions irreversible?

A

They have an extremely high activation energy

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5
Q

Describe an ‘open system’.

A

Allow matter and energy to be exchanged with surroundings

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6
Q

Describe a ‘closed system’.

A

Allow energy, but not matter, to be exchanged with surroundings

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7
Q

Explain why equilibrium is considered “dynamic”.

A

Dynamic means constant change. At equilibrium reaction is still occurring.

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8
Q

What type of system (open/closed) can equilibrium occur in?

A

Closed system

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9
Q

What is happening to the concentration of reactants and products in a system at equilibrium?

A

There’s no change in their concentration

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10
Q

If a system is at equilibrium, describe what you would macroscopically observe.

A

There would be no observable change

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11
Q

Describe what is occurring on an atomic/molecular level during dynamic equilibrium.

A

Forwards and reverse reaction occurring

Constant molecular change

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12
Q

Explain why the vapour pressure of a liquid (e.g. water) is at equilibrium in a closed system.

A

In an open system gas would escape meaning equilibrium wouldn’t be reached

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13
Q

On a concentration-time graph, what is plotted on the x-axis and what is plotted on the y-axis?

A 
x-axis = time
y-axis = concentration
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14
Q

As a system approaches equilibrium, does the rate of the forwards increase or decrease? Why?

A

Decrease, because the concentration of reactants is decreasing

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15
Q

As a system approaches equilibrium, does the rate of the reverse increase or decrease? Why?

A

Increase, because the concentration of products is increasing

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16
Q

On a concentration-time graph, what feature indicate that a system is at equilibrium?

A

The straight line which shows no change in concentration

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17
Q

List three factors that, if altered, can shift the position of equilibrium.

A

Concentration, temperature, volume/pressure

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18
Q

State Le Chatelier’s Principle.

A

If an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change

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19
Q

In a reversible reaction, increasing the concentration of reactants will shift equilibrium to the right. Explain why using collision theory.

A

It increases the number of collisions that occur in the reaction

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20
Q

On a concentration-time graph, an increase (or decrease) in ALL species indicates that ______ was changed.

A

Volume

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21
Q

Changing the pressure of a gaseous system can shift equilibrium. Explain what feature of a reaction determines whether it shifts left or right.

A

The number of gas particles in the reactants/products. The number of moles of gas of either side of the equations shows this.

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22
Q

How will the addition of an inert gas affect the equilibrium of a gaseous system?

A

No effect on the equilibrium, it doesn’t change concentrations

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23
Q

How will diluting an aqueous system affect the position of equilibrium? (What determines whether it subsequently shifts left or right)

A

It decreases concentration of all species

Position of equilibrium would move to the side with more particles

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24
Q

How does the addition of a catalyst affect the position of equilibrium?

A

Catalyst doesn’t affect the position of equilibrium

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25
If the temperature of a system is changed, what feature of a chemical reaction will determine whether the equilibrium shifts left or right?
Whether or not its exothermic or endothermic
26
Explain why increasing the temperature of an exothermic reaction will shift equilibrium to favour the reverse direction.
There’s more activation energy available to complete the reverse reaction
27
On a concentration-time graph, what type of ‘change’ causes a gradual shift in the concentration of reactants/products?
Change in temperature
28
State the formula for the equilibrium expression (aka equilibrium law).
aA+bB⇌ cC+dD | Kc= ([C]^c [D]^d [A]^a [B]^b )
29
Define a heterogeneous equilibrium system.
Reactants and products are a mixture of phases | Hetero = different states of matter
30
Define a homogenous equilibrium system.
Reactants and products are in the same phase | Homo = same states of matter
31
In a heterogeneous equilibrium system, which ‘states’ are included in the equilibrium expression?
Gas and aqueous | solids and liquids aren’t included
32
In a homogeneous equilibrium system, which ‘states’ are included in the equilibrium expression?
ALL states. (Every species).
33
If K >> 1, what does this indicate about the position of equilibrium?
``` Much bigger (10^4) Reaction favours the products (right) ```
34
If K = 1, what does this indicate about the position of equilibrium?
Same amount of products and reactants (can be slightly different)
35
If K << 1, what does this indicate about the position of equilibrium?
``` Much smaller (10^-4) Reaction favours the reactants (left) ```
36
What is the “reaction quotient, Qc” used for?
It’s the value of the equilibrium expression calculated at any time during the reaction
37
What is the formula for Qc?
aA+bB⇌ cC+dD | Qc= ([C]^c [D]^d [A]^a [B]^b)
38
What concentrations can be substituted into Kc?
The concentration at equilibrium
39
What concentrations can be substituted into Qc?
The concentrations from any time in the reaction
40
If Qc < Kc, which direction will the system proceed in to reach equilibrium?
System shifts to the right to produce more products and reach equilibrium
41
If Qc = Kc, what does this tell us about the system?
System is at equilibrium
42
If Qc > Kc, which direction will the system proceed in to reach equilibrium?
System shifts to the left to produce more reactants and reach equilibrium
43
What factor/s affect the value of Kc?
Temperature
44
If a chemical equation is reversed, how is the value of KC affected?
The Kc value is inverse
45
If the coefficients of a chemical equation are doubled, how is the value of KC affected?
The Kc value is squared
46
If the coefficients of a chemical equation are halved, how is the value of KC affected?
The Kc value is the square root of the original value
47
What does a RICE table stand for? (R = …, I = …)
``` R = Reaction I = Initial Concentration C = Change/Coefficients E = Equilibrium Concentration ```
48
What assumption can be made when the value of KC is very small?
[Reactants]initial ≈ [Reactants]equilibrium
49
Define a Bronsted-Lowry acid.
A substance behaves as an acid when it donates a proton
50
Define a Bronsted-Lowry base.
A substance behaves as a base when it accepts a proton
51
Define a monoprotic acid.
Donates only one proton per molecule on dissociation
52
Give 2 examples of a monoprotic acid.
- HCl - HBr - HNO3 - CH3COOH (acetic acid/ethanoic acid – the acid in vinegar)
53
Define a polyprotic acid.
Donates more than one proton per molecule - Diprotic acids donate 2 (H2SO4) - Triprotic acids donate 3 (H3PO4)
54
Define a strong acid.
``` Fully ionised (dissociates into H+ and anion) ```
55
Define a weak acid.
Partially ionised
56
Define a strong base.
Fully dissociates
57
Define a weak base.
Partially dissociates
58
When writing the dissociation reaction of a strong acid, what arrow is used in the equation?
-->
59
When writing the dissociation reaction of a weak acid, what arrow is used in the equation?
⇌
60
Does a strong or weak acid have a higher electrical conductivity? Why?
Strong acids have a higher electrical conductivity, its fully dissociated meaning more ions present
61
Distinguish between concentration and strength.
Concentration: - Amount (in moles) of solute per unit of volume (litres) - concentrated and dilute Strength: - Its ability to ionise in a solution - Strong and weak
62
Does low pH mean an acid is strong?
Low pH doesn’t mean it’s a strong acid, it could be a weak acid but concentrated
63
What are the strong acids?
``` Important: Hydrochloric acid Hydrobromic acid Hydroiodic acid Sulfuric acid Nitric acid ``` Others: chloric acid perchloric acid
64
What are the strong bases?
``` Potassium hydroxide (KOH) Sodium hydroxide (NaOH) Barium hydroxide (Ba(OH)2) Caesium hydroxide (CsOH) Sodium hydroxide (NaOH) Strontium hydroxide (Sr(OH)2) Calcium hydroxide (Ca(OH)2) Lithium hydroxide (LiOH) Rubidium hydroxide (RbOH) ```
65
What are the rules for naming acids?
AHHHHHHHHHHHHHHH
66
What is a conjugate acid?
The acid that is formed when a base accepts a proton from an acid
67
What is a conjugate base?
The base that is formed when an acid donates a proton to a base
68
What is the conjugate base of HCl?
Cl^-
69
What is the conjugate base of HNO3?
NO3^-
70
What is the conjugate acid of OH-?
H2O
71
If I have a strong acid, is the conjugate base strong or weak?
Weak
72
If I have a weak base, is the conjugate acid strong or weak?
Strong
73
Which acid would produce a stronger conjugate base: Nitric acid or methanoic acid?
Methanoic acid (a weak acid) would produce a stronger conjugate base
74
Define “amphiprotic”.
A substance that can gain or lose a hydrogen ion to act as an acid or base
75
Explain how H2PO4- is amphiprotic.
It can give or gain a proton Acid: H2PO4^- + H2O ⇌ HPO42^- + H3O^+ Base: H2PO4^- + H2O ⇌ H3PO4 + OH^-
76
Explain what a buffer solution is.
A solution containing both a weak acid/base and its conjugate; a solution that can partially resist changes in pH
77
A buffer solution is an aqueous solution consisting of a mixture of either ___ or ____.
A weak acid and its conjugate base | A weak base and its conjugate acid
78
Explain how a buffer solution is able to resist changes in pH.
The reaction will produce whatever side of the reaction which has the opposite (eg acid = base, base = acid)
79
Explain how the H2CO3/HCO3- buffer system acts as a buffer.
H2CO3 is a weak acid and HCO3^- is its conjugate base
80
What is the generalised formula for reactions of acids and water?
HA + H2O ⇌ A^- + H3O^+
81
Would a strong acid have a small or large Ka value?
Large (products favoured)
82
Would a weak acid have a small or large Ka value?
Small (reactants favoured)
83
Recall the formula for the acid dissociation constant.
Ka=[H3 O^+][A^-] | [HA]
84
Is hydrochloric acid a strong or weak acid?
Strong | Ka = 1.3 x 10^6
85
Is nitric acid a strong or weak acid?
Strong | Ka = 2.4 x 10^1
86
Is sulfuric acid a strong or weak acid?
Strong | Ka = 1.0 x 10^3
87
Are carboxylic acids strong or weak acids?
Weak | Ka = 1.0 x 10^-4
88
Is carbonic acid a strong or weak acid?
Weak | Ka = 4.4 x 10^-7
89
Recall the formula for the base dissociation constant.
Kb =[BH^+ ][OH^-] | [B]
90
Would a strong base have a small or large Kb value?
Large (reactants favoured)
91
Would a weak base have a small or large Kb value?
Small (products favoured)
92
Is sodium hydroxide a strong or weak base?
Strong
93
Are group 1 hydroxides strong or weak base?
Strong
94
Is barium hydroxide a strong or weak base?
Strong
95
Is ammonia a strong or weak base?
Weak
96
Are amines a strong or weak base?
Weak
97
Recall the formula for the percentage ionisation of an acid.
= [A^-] | [HA] x 100%
98
Recall the formula for convert a Ka value into a pKa value.
pKa=-log10 (Ka)
99
Would a strong acid have a small or large pKa value?
Small
100
Would a weak acid have a small or large pKa value?
Large
101
Recall the formula for convert a Kb value into a pKb value?
pKb=-log10(Kb)
102
Recall the formula that relates pka to pkb.
14= pKa + pKb

Chemistry (Year 12) (3 decks)

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