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ADVANCED HIGHER CHEMISTRY > Chemical Equilibrium > Flashcards

Chemical Equilibrium Flashcards

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1
Q

When is a chemical reaction in equilibrium

A

A chemical reaction is in equilibrium when the composition of the reactants and products remains constant indefinitely.

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2
Q

Which constant characterises the equilibrium composition of the reaction mixture

A

The equilibrium constant ( K ) characterises the equilibrium composition of the reaction
mixture.

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3
Q

What does the value of an equilibrium constant indicate

A

The value of an equilibrium constant indicates the position of equilibrium.

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4
Q

What units do equilibrium constants have

A

Equilibrium constants have no units.

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5
Q

What causes a change in K for endothermic reactions

A

For endothermic reactions, a rise in temperature causes an increase in K and the yield of
the product is increased.

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6
Q

What causes a change in K for exothermic reactions

A

For exothermic reactions, a rise in temperature causes a decrease in K and the yield of
the product is decreased.

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7
Q

What does the presence of a catalyst not affect

A

The presence of a catalyst does not affect the value of the equilibrium constant.

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8
Q

Where is the equilibrium in water and aqueous solutions

A

In water and aqueous solutions there is an equilibrium between the water molecules and
hydronium (hydrogen) and hydroxide ions.

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9
Q

This ionisation of water can be represented by:

A

H20 + H20 ————> H30+ + OH-

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10
Q

What is the feature of water

A

Water is amphoteric (can react as an acid and a base)

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11
Q

What does the numerical value of the equilibrium constant depend on

A

The numerical value of the equilibrium constant depends on the reaction temperature and is independent of concentration and/or pressure.

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12
Q

What are the concentrations of pure solids and pure liquids at equilibrium taken as

A

The concentrations of pure solids and pure liquids at equilibrium are taken as constant and given a value of 1 in the equilibrium expression.

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13
Q

What is the disassociation constant for water known as and represented by

A

The dissociation constant for the ionisation of water is known as the ionic product and is
represented by Kw :

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14
Q

Kw

A

Kw = [H3O+] [OH-]

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15
Q

Where must the reaction take place fro equilibrium to be established

A

For an equilibrium to be established the reaction must take place in a closed system

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16
Q

A closed system is..

A

A closed system is one which energy to be transferred to or from surroundings but no the reactants or products. Reactants form products and products form reactants.

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17
Q

What is dynamic equilibrium

A

The rate of the forward reaction equals the rate of the reverse reaction

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18
Q

For the general reaction

A

aA +bB <———-> cC + dD

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19
Q

K is given by the equation

A

K = [products] /[reactants] = [C]^c. [D]^d / [A]^a. [B]b

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20
Q

What are a b c d

A

The stoichiometric coefficients in the balanced equation

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21
Q

If value of K is < 10^-3

A

Effectively no reaction

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22
Q

If value of K is 10^-3 to 10^3

A

Significant quantities of reactants and products at equilibrium

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23
Q

If value of K is >10^3

A

Reaction is effectively complete

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24
Q

When K = 1

A

[products] = [reactants]

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25
Q

What value are pure solids and solvents (liquids) given

A

It is given the concentration value of 1 in equilibrium equation

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26
Q

How is K calculated for reaction involving gases

A

K is calculated using the partial pressure of gases involved

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27
Q

For the general reaction involving gases

A

aA + bB <=> cC + dD

Kp = P[products] / P[reactants] = PC^c. PD^d/ PA^a. PB^b

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28
Q

What can be used in place of partial pressures

A

Concentrations of gases can be used in place of partial pressures

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29
Q

When is a equilibrium describes as homogeneous

A

An equilibrium can be describes as homogeneous I.e all the species are in one state

2NOCL(g) <——-> 2NO (g) + CL2 (g)

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30
Q

When is a catalyst describes as heterogenous

A

The species are in more than one state

CaCO3 (s) <———> CaO (s) + CO2(g)

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31
Q

La chatelier’s principle

A

La chateliers principle states that any change in a system at equilibrium results in a shift of the equilibrium in the direction which minimises the change

32
Q

What does concentration change and not change

A

At a given temperature changes in concentration may alter the position of equilibrium by these changes do not alter the value of K

33
Q

What effect does pressure (only applies to gases) have on the value of K

A

At a given temperature changes in pressure May later the position of equilibrium but these changes do not alter the value of K

34
Q

What happens if there are equal numbers of moles of gas molecules on each side of a reaction

A

A change in pressure will have no effect on equilibrium position since there is equal no of moles or gas on each side

35
Q

What happens if there are equal numbers of moles of gas molecules on each side of a reaction

A

A change in pressure will have no effect on equilibrium position since there is equal no of moles or gas on each side

36
Q

What happens when the temperature of a system is raised

A

When the temperature of a system is raised the system will move in a direction to reduce the temperature I.e the endothermic reaction will be favoured.

37
Q

Is K affected by changes in temperature

A

K is affected by changes in temperature

38
Q

Summary of factors affecting K

A

K is unaffected by changes in
- concentration
- pressure

K is affected by changes in temperature an increase in temperature will shift the equilibrium in the direction of the endothermic reaction.

39
Q

What are acids historically defined as

A

Historically acids were defined as producing hydrogen ions in solution and bases as producing hydroxide ions in solution

40
Q

What does the Brønsted-Lowry define acids and bases as

A

An acid is any substance capable of donating a proton.
A base is any substance capable of accepting a proton.

41
Q

What species is left when an acid donates a proton

A

When an acid donates a proton the species left is called the conjugate base of that acid

42
Q

When is a conjugate base formed for every acid

A

For every acid there is a conjugate base formed by the loss of a proton

43
Q

What species is formed when a base accepts a proton

A

When a base accepts a proton the species formed is called the conjugate acid of that base

44
Q

What is formed for every base by the gain of a proton

A

For every base there is a conjugate acid formed by the gain of a proton

45
Q

What is the value of Kw at 25°C

A

The ionic product of water (Kw) for water has the value of 1.0x 10^-14 at 25°C since the reaction is endothermic

46
Q

What happens to the ionic product of water as temperature increases

A

Ten ionic product of water increases as the temperature increases. Therefore the pH of the water decreases as the temperature increases it becomes more acidic.

47
Q

The ph of any aqueous solutions of a strong acid or alkali can be calculated using:

A

pH = -log[H+]

48
Q

What is the disassociation for strong acids and strong bases

A

Strong acids and strong bases are completely dissociated into ions in aqueous solution.

49
Q

What is the disassociation for weak acids and weak bases

A

Weak acids and weak bases are only partially dissociated into ions in aqueous solution.

50
Q

Examples of strong acids

A

Examples of strong acids include hydrochloric acid, sulfuric acid and nitric acid.

51
Q

Weak acid examples

A

Ethanoic acid, carbonic acid and sulfurous acid are examples of weak acids.

52
Q

Strong bases example

A

Solutions of metal hydroxides are strong bases.

53
Q

Weak bases example

A

Ammonia and amines are examples of weak bases.

54
Q

What is Ka

A

ka is known as the acid disassociation constant and is a measure of the strength of the acid

55
Q

The smaller the value of Ka

A

The smaller the value of Ka the weaker the acid

56
Q

How can the disassociation constant be expressed

A

pKa = -log Ka

57
Q

The approximate pH of a weak acid can be calculated using

A

pH = 1/2 pka - 1/2 log10c

58
Q

What does the name of the salt produced depend on

A

The name of the salt produced depends on the acid and base used.

59
Q

What does a soluble salt of a strong acid and a base produce

A

A soluble salt of a strong acid and a strong base dissolves in water to produce a neutral
solution.

60
Q

What does a soluble salt of a weak acid and a strong base dissolve to produce

A

A soluble salt of a weak acid and a strong base dissolves in water to produce an alkaline
solution.

61
Q

What does a soluble salt of a strong acid and a weak base dissolve to produce

A

A soluble salt of a strong acid and a weak base dissolves in water to produce an acidic
solution.

62
Q

What is a buffer solution

A

A buffer solution is one in which the pH remains approximately constant when small
amounts of acid, base or water are added.

63
Q

What is an acid buffer

A

An acid buffer consists of a solution of a weak acid and one of its salts made from a strong base

64
Q

How does an acid buffer solution work

A

In an acid buffer solution the weak acid provides hydrogen ions when these are removed
by the addition of a small amount of base. The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions produced by the addition of a small amount of acid.

65
Q

What is a basic buffer

A

A basic buffer consists of a solution of a weak base and one of its salts.

66
Q

How does a basic buffer solution work

A

In a basic buffer solution the weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed.

67
Q

An approximate pH of an acid buffer solution can be calculated from its composition and
from the acid dissociation constant:

A

PH = pKa -log10 [acid] / [salt]

68
Q

What is the relationship between pH and hydrogen ion concentration given by

A

PH = -log10 [H30+] and [H3O+] = 10 ^-PH

69
Q

Which solutions have a weakly acidic nature

A

The weakly acidic nature of solutions of carboxylic acids, sulfur dioxide and carbon dioxide can be explained by reference to equations showing the equilibria.

70
Q

Which solutions have a weakly alkaline nature

A

The weakly alkaline nature of a solution of ammonia or amines can be explained by
reference to an equation showing the equilibrium.

71
Q

What are similarities and differences I’d equimolar solutions of weak and strong acids (or bases)

A

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.

72
Q

The acid disassociation constant is represented by Ka:

A

Ka = [H3O+] [A-]/ [HA]

73
Q

An approximate pH of an acid buffer solution can be calculated from its composition and from the acid dissociation constant:

A

pH = pKa - log 10 [acid]/[salt]

74
Q

The acid indicator dissociation constant is represented as KIn and is given by the following expression

A

Kin = [H3O+] [In-] / [HIn]

75
Q

What can suitable indicators be selected by

A

Suitable indicators can be selected from pH data, including titration curves.

76
Q

What is the expression for the pH range over which a colour change occurs

A

The pH range over which a colour change occurs can be estimated by the expression:
pH = pKin +- 1

77
Q

In aqueous solution the colour of an acid is….

A

In aqueous solution the colour of an acid indicator is distinctly different from that of its

ADVANCED HIGHER CHEMISTRY (17 decks)

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