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X A2 chemistry > unit 4 section three. equilibrium and pH > Flashcards

unit 4 section three. equilibrium and pH Flashcards

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1
Q

What is dynamic equilibrium?

A

When the rate of the forward reaction is equal to the rate of the backward reaction meaning the amounts of both are the constant.

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2
Q

what are the conditions needed for dynamic equilibrium?

A

Constant temperature and closed system.

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3
Q

What is the haber process?

A

N₂ + 3H₂ = 2HN₃

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4
Q

How to the equilibrium constant found?

A

divide the concentration of the products by that of the reaction.

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5
Q

If an equilibrium reaction has solids and gases or solids and liquids, how is Kc found?

A

Ignore the concentrations of the solids. If you have gases and liquids, you have to use Kp

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6
Q

what is total pressure equal to?

A

The total pressure of a gas mixture is the sum of all the partial pressures of the individual gases.

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7
Q

what is the mole fraction of a gas?

A

Number of moles of a gas / total number of moles of all the gases in the mixture.

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8
Q

How can the partial pressure of a gas be determined with the mole fraction of it?

A

Partial pressure = mole fraction X total pressure of the mixture.

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9
Q

How is Kp found?

A

It is the same way for finding Kc, but you use pressure and not concentration.

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10
Q

How is Kp found for heterogeneous equilibrium?

A

Ignore the solids and liquids.

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11
Q

What does moving equilibrium to right mean?

A

More products

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12
Q

What is Le chatelier’s principle?

A

If there’s a change in pressure or temperature, the equilibrium will move to help counteract the change.

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13
Q

Is Kp affected by pressure?

A

No.

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14
Q

What is the effect of a catalyst on the position of equilibrium?

A

Catalysts have no effect but they do mean that it comes about faster.

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15
Q

What is the effect of temperature on the position of equilibrium?

A

Increase it and it will go in the endothermic direction ( positive enthaply)
Decrease it and it will go in exothermic direction. (- enthaply)

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16
Q

Basics of collision theory.

A

particles must collide in the right direction, with enough Ke.

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17
Q

Is the haber process endo or exothermic?

A

Exo meaning that it produces heat. For a high yield a low temperature would be favored.

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18
Q

When does balanced equlibrium happen?

A

the total entropy is 0.

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19
Q

At what temperature does the entropy of the system = 0

A

divide the enthalpy change by the system entropy.

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20
Q

does the haber process happen at equilibrium?

A

No as it is never a closed system. The gas mixture is always being removed and unreacted nitrogen and hydrogen are recycled.

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21
Q

what is atom economy?

A

mass of the atoms in product / mass of the atoms in reactants X 100

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22
Q

How can atom economy be increased?

A

Recycle reactants that didn’t react and find alternative routes for reactions with less steps.

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23
Q

In terms of the reaction entropy, when will a reaction take place?

A

If the total entropy is less than -100 they are unlikely to happen even with correct conditions
If is is between -100 and 0 then it can be done economically.
If it is greater than 0 it can happen on its own.

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24
Q

what must be considered as an industrial process is developed?

A

Will the reaction go
how fast is it
can the atom economy be increased
are there ways to reduce the energy consumption
what safety procedures need to be put into place.

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25
Q

What are the units for Kp?

A

It will always be in terms of pascals as pressure is used instead of concentration.

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26
Q

What is the equilibrium constant an indication of?

A

The ratio is product to reactants. If it is large, lots of products will be formed, if it is 1, it be be in equal amounts. If less than one, lots of reactants.

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27
Q

Why will a spontaneous reaction have a high equilibrium constant?

A

For it to be spontaneous it will produce a lot of product.

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28
Q

what equation links the equilibrium constant to the total entropy?

A

total = R*Ln(K).
R is the gas constant. (8.31 J K^-1 mol^-1)
Kp and Kc can be used.

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29
Q

What will a reaction with an equlibruim constant of less than 10^-10 do?

A

It will not take place.

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30
Q

What will a reaction with an equlibruim constant of more than 10^10 do?

A

It will go to completion.

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31
Q

What will a reaction with an equlibruim constant between 10^-10 and 10^10 do?

A

It will be a reversible reaction.

32
Q

What will happen if the total entropy of a reaction is positive?

A

The reaction will be spontaneous and will happen on its own.

33
Q

How can you use the total entropy, to find the position of equilibrium?

A

Use total = R*Ln(K) to find K.

34
Q

What is total entropy equal to?

A

System + surroundings.

Surroundings = -ΔH/T. (T in kelvin)

35
Q

what are bronsted lowry acids?

A

Proton donors in water (gives H+ ions).
These will combine with water to give H3O+
HA + H₂O = H₃O⁺ + A⁻

36
Q

What are bronsted lowry bases?

A

Proton accepters. They take H+ ions from water

B + H₂O = BH⁺ + OH⁻

37
Q

Why are strong acids strong?

A

They ionize almost completely in water. Strong bases will do the same.

38
Q

Why are weak acids or bases weak?

A

They only slightly ionize in water. Only small amounts of H+ or OH- ions are formed. An equilibrium which lies to the left will be set up.

39
Q

What do strong acids and bases do in water?

A

They will set up an equilibrium which is far to the right.

40
Q

What is the equation for acids and bases reacting?

A

HA + B ⇌ BH⁺ + A⁻. Water can act as both an acid or a base in these circumstances.

41
Q

What is a conjugate pair?

A

A pair in an acid base reaction that are connected by a H⁺. One of them will be a base and the other an acid.

42
Q

What is the acid base equilibrium that exists in water?

A

2H₂O ⇌ H₃O⁺ + OH-. Equilibrium is on the far left and the concentration of water is considered to be constant.

43
Q

What is Kw?

A

The ionic product of water. Equal to the concentration of H+ * OH-. at 298 K it is 10^-14 mol²dm⁻⁶

44
Q

what is pKw?

A

-log Kw

45
Q

what is a neutral solution?

A

One where the concentration of H+ is equal to the concentration of OH⁻

46
Q

What is pH equal to?

A

-log (H⁺)

47
Q

What is Ka?

A

The acid dissociation constant. Used for weak acids that don’t fully dissociate in water.
Ka = [H⁺]² / [HA]

48
Q

What assumptions do we make when we find Ka?

A

Only a small amount of the acid dissolves so the concentration at the start is the same at equlibruim.
All the H⁺ ions come from the acid so the concentration of H⁺ = conc of A⁻

49
Q

what is pKa?

A

-log (Ka)

50
Q

If a strong acid is diluted by a factor of 10, what will happen to the pH?
What about a weak acid?

A

Strong acid. pH will increase by 1. For a weak acid it will increase by 0.5

51
Q

What does the graph of a titration have for axises?

A

pH by volume of alkali added

52
Q

What do titration graphs look like?

A

they will have 2 nearly horizontal sections and one nearly vertical one.
However if all the reagents are weak, there will be a diagonal instead of a vertical line.

53
Q

What does the vertical bit on a titration graph mean?

A

It is the end point. All the acid has just been neutralised and a small amount if alkali will cause a large change in pH.

54
Q

colour of methyl orange.

A

acid=red
base=yellow
changes at pH of 3.1-4.4

55
Q

colour of phenolphthalein

A

acid= colourless
base=pink.
changes at pH of 8.3-10

56
Q

what indicator is used for strong acid, strong alkali titration?

A

Methyl orange or phenolphthalein as there is rapid change over the range of both indicators.

57
Q

what indicator is used for strong acid, weak alkali

titration?

A

Methyl orange

58
Q

what indicator is used for weak acid, strong alkali titration?

A

phenolphthalein

59
Q

what indicator is used for weak acid, weak alkali

titration?

A

Use a pH meter.

60
Q

what titration graph can you use to find the pka of an acid?

A

weak acid/ strong base

61
Q

how is pKa found from a weak acid/strong base titration>

A

find the pH at the half equivalence point. This is when half the acid has been neutralised and half the alkali has been added. At this point the pH is equal to pKa

62
Q

what is a buffer?

A

A buffer is a solution hat resists changes in pH when small amounts of acid or alkali are added.

63
Q

what is an acidic buffer?

A

A weak acid mixed with one of its salts.

64
Q

how does an acidic buffer work?

A

The salt will fully dissociate into its ions, while the acid will only slightly dissociate. This means that in the solution there are many acid molecules and acid ions.
An equilibrium will be set up.

65
Q

what is the buffer solution in a cell?

A

A cell needs a constant pH. It is controlled by

66
Q

How is the pH of an acidic buffer found?

A

Ka= [H]*[ion from salt] / [acid]

This assumes that the salt fully dissociates and that the acid hardly dissociates at all.

67
Q

If asked to give an expression for Ka of an acid, what should you give?

A

the concentrations of the 2 ions given when the acid dissociates over the concentration of the acid. This makes it clear that the concentrations of the ions are being used.

68
Q

How do you explain that something is a buffer?

A

The acid or base partially ionised while the salt is fully ionised.
There is a large concentration of HA and of A⁻
HA + OH⁻=A⁻+H20
A⁻ + H⁺ = HA. Make use of these two equations.
Name ions and acid and say how they form

69
Q

If asked to give the expresstion for Kp, what do you give?

A

Much the same as it is for Kc but instead of [] you use p()

70
Q

what is the colour of N2O4 and NO2

A

The former colourless, the latter dark brown

71
Q

N2O4 ⇌ 2NO₂ How could the progress of this reaction be measured?

A

Look for a change in colour

Measure the total volume or the total gas pressure.

72
Q

Suggest why the concentration of hydrogen ion is not 0.2 mol dm^-3 in 0.1 mol dm^-3 sulphuric acid?

A

second ionisation suppressed by the first.

73
Q

What are the relative pH s of the acid and the salt of the acid?

A

When half the acid has been neutralised they are the same.

74
Q

How do you find the pH at half the equivalence point?

A

pKa of the weak acid.=-log Ka

75
Q

In an ammonia buffer solution, what happens is more H+ is added?

A

Reacts with ammonia for NH4+

76
Q

Why is it that when doing a titration, some reactants have a significantly higher concentration than others?

A

Some that their concentration stays the same through out.

77
Q

What are the pHs of the equivalence points in acid base reactions

A

Both strong =7
Strong acid weak base = 4-6
Weak acid strong base = 8-9

X A2 chemistry (12 decks)

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