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

Unit 3: Topic 1 Flashcards

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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
Q

If the temperature of a system is changed, what feature of a chemical reaction will determine whether the equilibrium shifts left or right?

A

Whether or not its exothermic or endothermic

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26
Q

Explain why increasing the temperature of an exothermic reaction will shift equilibrium to favour the reverse direction.

A

There’s more activation energy available to complete the reverse reaction

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27
Q

On a concentration-time graph, what type of ‘change’ causes a gradual shift in the concentration of reactants/products?

A

Change in temperature

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28
Q

State the formula for the equilibrium expression (aka equilibrium law).

A

aA+bB⇌ cC+dD

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

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29
Q

Define a heterogeneous equilibrium system.

A

Reactants and products are a mixture of phases

Hetero = different states of matter

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30
Q

Define a homogenous equilibrium system.

A

Reactants and products are in the same phase

Homo = same states of matter

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31
Q

In a heterogeneous equilibrium system, which ‘states’ are included in the equilibrium expression?

A

Gas and aqueous

solids and liquids aren’t included

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32
Q

In a homogeneous equilibrium system, which ‘states’ are included in the equilibrium expression?

A

ALL states. (Every species).

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33
Q

If K&raquo_space; 1, what does this indicate about the position of equilibrium?

A 
Much bigger (10^4)
Reaction favours the products (right)
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34
Q

If K = 1, what does this indicate about the position of equilibrium?

A

Same amount of products and reactants (can be slightly different)

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35
Q

If K &laquo_space;1, what does this indicate about the position of equilibrium?

A 
Much smaller (10^-4)
Reaction favours the reactants (left)
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36
Q

What is the “reaction quotient, Qc” used for?

A

It’s the value of the equilibrium expression calculated at any time during the reaction

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37
Q

What is the formula for Qc?

A

aA+bB⇌ cC+dD

Qc= ([C]^c [D]^d
[A]^a [B]^b)

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38
Q

What concentrations can be substituted into Kc?

A

The concentration at equilibrium

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39
Q

What concentrations can be substituted into Qc?

A

The concentrations from any time in the reaction

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40
Q

If Qc < Kc, which direction will the system proceed in to reach equilibrium?

A

System shifts to the right to produce more products and reach equilibrium

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41
Q

If Qc = Kc, what does this tell us about the system?

A

System is at equilibrium

42
Q

If Qc > Kc, which direction will the system proceed in to reach equilibrium?

A

System shifts to the left to produce more reactants and reach equilibrium

43
Q

What factor/s affect the value of Kc?

A

Temperature

44
Q

If a chemical equation is reversed, how is the value of KC affected?

A

The Kc value is inverse

45
Q

If the coefficients of a chemical equation are doubled, how is the value of KC affected?

A

The Kc value is squared

46
Q

If the coefficients of a chemical equation are halved, how is the value of KC affected?

A

The Kc value is the square root of the original value

47
Q

What does a RICE table stand for? (R = …, I = …)

A 
R = Reaction
I = Initial Concentration
C = Change/Coefficients
E = Equilibrium Concentration
48
Q

What assumption can be made when the value of KC is very small?

A

[Reactants]initial ≈ [Reactants]equilibrium

49
Q

Define a Bronsted-Lowry acid.

A

A substance behaves as an acid when it donates a proton

50
Q

Define a Bronsted-Lowry base.

A

A substance behaves as a base when it accepts a proton

51
Q

Define a monoprotic acid.

A

Donates only one proton per molecule on dissociation

52
Q

Give 2 examples of a monoprotic acid.

A
  • HCl
  • HBr
  • HNO3
  • CH3COOH (acetic acid/ethanoic acid – the acid in vinegar)
53
Q

Define a polyprotic acid.

A

Donates more than one proton per molecule

  • Diprotic acids donate 2 (H2SO4)
  • Triprotic acids donate 3 (H3PO4)
54
Q

Define a strong acid.

A 
Fully ionised 
(dissociates into H+ and anion)
55
Q

Define a weak acid.

A

Partially ionised

56
Q

Define a strong base.

A

Fully dissociates

57
Q

Define a weak base.

A

Partially dissociates

58
Q

When writing the dissociation reaction of a strong acid, what arrow is used in the equation?

A

–>

59
Q

When writing the dissociation reaction of a weak acid, what arrow is used in the equation?

A

⇌

60
Q

Does a strong or weak acid have a higher electrical conductivity? Why?

A

Strong acids have a higher electrical conductivity, its fully dissociated meaning more ions present

61
Q

Distinguish between concentration and strength.

A

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
Q

Does low pH mean an acid is strong?

A

Low pH doesn’t mean it’s a strong acid, it could be a weak acid but concentrated

63
Q

What are the strong acids?

A 
Important:
Hydrochloric acid 
Hydrobromic acid
Hydroiodic acid
Sulfuric acid
Nitric acid

Others:
chloric acid
perchloric acid

64
Q

What are the strong bases?

A 
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
Q

What are the rules for naming acids?

A

AHHHHHHHHHHHHHHH

66
Q

What is a conjugate acid?

A

The acid that is formed when a base accepts a proton from an acid

67
Q

What is a conjugate base?

A

The base that is formed when an acid donates a proton to a base

68
Q

What is the conjugate base of HCl?

A

Cl^-

69
Q

What is the conjugate base of HNO3?

A

NO3^-

70
Q

What is the conjugate acid of OH-?

A

H2O

71
Q

If I have a strong acid, is the conjugate base strong or weak?

A

Weak

72
Q

If I have a weak base, is the conjugate acid strong or weak?

A

Strong

73
Q

Which acid would produce a stronger conjugate base: Nitric acid or methanoic acid?

A

Methanoic acid (a weak acid) would produce a stronger conjugate base

74
Q

Define “amphiprotic”.

A

A substance that can gain or lose a hydrogen ion to act as an acid or base

75
Q

Explain how H2PO4- is amphiprotic.

A

It can give or gain a proton

Acid: H2PO4^- + H2O ⇌ HPO42^- + H3O^+
Base: H2PO4^- + H2O ⇌ H3PO4 + OH^-

76
Q

Explain what a buffer solution is.

A

A solution containing both a weak acid/base and its conjugate; a solution that can partially resist changes in pH

77
Q

A buffer solution is an aqueous solution consisting of a mixture of either ___ or ____.

A

A weak acid and its conjugate base

A weak base and its conjugate acid

78
Q

Explain how a buffer solution is able to resist changes in pH.

A

The reaction will produce whatever side of the reaction which has the opposite (eg acid = base, base = acid)

79
Q

Explain how the H2CO3/HCO3- buffer system acts as a buffer.

A

H2CO3 is a weak acid and HCO3^- is its conjugate base

80
Q

What is the generalised formula for reactions of acids and water?

A

HA + H2O ⇌ A^- + H3O^+

81
Q

Would a strong acid have a small or large Ka value?

A

Large (products favoured)

82
Q

Would a weak acid have a small or large Ka value?

A

Small (reactants favoured)

83
Q

Recall the formula for the acid dissociation constant.

A

Ka=[H3 O^+][A^-]

[HA]

84
Q

Is hydrochloric acid a strong or weak acid?

A

Strong

Ka = 1.3 x 10^6

85
Q

Is nitric acid a strong or weak acid?

A

Strong

Ka = 2.4 x 10^1

86
Q

Is sulfuric acid a strong or weak acid?

A

Strong

Ka = 1.0 x 10^3

87
Q

Are carboxylic acids strong or weak acids?

A

Weak

Ka = 1.0 x 10^-4

88
Q

Is carbonic acid a strong or weak acid?

A

Weak

Ka = 4.4 x 10^-7

89
Q

Recall the formula for the base dissociation constant.

A

Kb =[BH^+ ][OH^-]

[B]

90
Q

Would a strong base have a small or large Kb value?

A

Large (reactants favoured)

91
Q

Would a weak base have a small or large Kb value?

A

Small (products favoured)

92
Q

Is sodium hydroxide a strong or weak base?

A

Strong

93
Q

Are group 1 hydroxides strong or weak base?

A

Strong

94
Q

Is barium hydroxide a strong or weak base?

A

Strong

95
Q

Is ammonia a strong or weak base?

A

Weak

96
Q

Are amines a strong or weak base?

A

Weak

97
Q

Recall the formula for the percentage ionisation of an acid.

A

= [A^-]

[HA] x 100%

98
Q

Recall the formula for convert a Ka value into a pKa value.

A

pKa=-log10 (Ka)

99
Q

Would a strong acid have a small or large pKa value?

A

Small

100
Q

Would a weak acid have a small or large pKa value?

A

Large

101
Q

Recall the formula for convert a Kb value into a pKb value?

A

pKb=-log10(Kb)

102
Q

Recall the formula that relates pka to pkb.

A

14= pKa + pKb

Chemistry (Year 12) (3 decks)

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