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A level chemistry > 5.1 rates, equilibrium and pH > Flashcards

5.1 rates, equilibrium and pH Flashcards

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1
Q

what is the formula for the rate of reaction

A

change in concentration / time

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2
Q

define rate of reaction

A

the change in concentration of a reactant or a product per unit time

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3
Q

what is the order with respect to the reactant

A

the power to which the concentration of a reaction is raised in the rate equation

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4
Q

define the rate constant, k

A

the constant that links the rate of reaction with the concentration of the reactants raised to the powers of their orders in the reaction

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5
Q

what is overall order

A

the sum of the individual orders

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6
Q

what is the equation for the rate of a reaction

A

change in concentration / tie

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7
Q

Define zero order

A

the rate is unaffected by the changing concentration of the reactant

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8
Q

define first order

A

the rate is directly proportional to the concentration
So, if the concentration of the reactant increases by 2 times so will the concentration

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9
Q

Define second order

A

The change in rate will be equal to the change in concentration squared

If the reactant increases by 2 times the rate increases by 2^2 = 4

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10
Q

What is the rate equation

A

Rate = k[A]x[B]y[C]z

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11
Q

define half life

A

the time taken for half the concentration of a reactant to reduce by half

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12
Q

What kind of concentration-time graph does a zero order rection produce

A

a straight-line graph with the concentration decreasing at a constant rate and the half-life decreases with time

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13
Q

what kind of concentration time graph does a first order reaction produce in respect to half-life

A

A curved graph with a constant half-life and halving of the reactant concentration occurring at equal time intervals

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14
Q

How can you use half-life to find the rate constant

A

Because first order reactions have constant half-lives the value of the half-life can be used to determine rate constant

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15
Q

give the equation of determining the rate constant from half-life

A

K = ln2/t1/2
K = natural log 2 / half life

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16
Q

What is a clock reaction

A

reactions that produce visible changes
And in these instances, the time taken for the visible event to occur is inversely proportional to the initial rate

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17
Q

give an example of a clock reaction

A

the reaction between sodium thiosulfate and hydrochloric acid

A cross is drawn and placed underneath the beaker and time taken for it to become not visible is measured

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18
Q

What kind of graph would you plot to see the effect of concentration on rate of reaction

A

1/T against concentrtion

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19
Q

What would a rate-concentration graph look for a zero order reaction

A

it would be a straight line as the changes in the concentration have no effect on the rate

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20
Q

What would a rate-concentration graph look like for a first order reaction

A

It would be a straight-line with a positive gradient

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21
Q

How would you determine the rate constant from first order rate-concentration graphs

A

k = rate / concentration
k = gradient (change in y/ change in x)

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22
Q

How would the rate-concentration graph look like for a second order reaction

A

it would be a slightly curved line with a positive gradient

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23
Q

What is the effect of temperature on the rate constant

A

the rate constant increases with temperature because the concentrations remain the same in the rate equation

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24
Q

What graphs are associated with Arrhenius plots

A

ln k -1/t graphs

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25
Q

What is the intercept equal to in the Arrhenius plots

A

it is equal to natural log A

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26
Q

What is the gradient equal to in the Arrhenius plots

A

It is equal to -Ea/ R with R as the gas constant
This can easily be rearranged to find the activation energy
Ea=-R/gradient

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27
Q

what is a colourimeter

A

monitors the concentration of a reactant or a product by measuring the amount of light passing through a substance

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28
Q

Define partial pressure

A

the pressure an individual gas in a substance would exert if it occupied a whole reaction vessel on its own

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29
Q

describe how you would figure out the partial pressure exerted by a gas

A

mole fraction * total pressure

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30
Q

what is Kp

A

The equilibrium constant for reactions involving gasses

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31
Q

What is the equation for Kp

A

(Pc)(Pd)/(Pa)(Pb) the multiplication sum partial pressure of the products divided by the multiplied partial pressures of the reactants

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32
Q

How do changes in pressure affect K

A

They have no effect

33
Q

What is a Bronsted- Lowry acid

A

A proton/H+ donor

34
Q

What is a Bronsted-Lowry base

A

A proton acceptor

35
Q

What are conjugate acid-base pairs

A

A set of two species that transform into each other through the gain or loss of a proton

36
Q

What is the definition of an alkali

A

A base that dissolves in water forming OH- ions

37
Q

Define neutralisation

A

A chemical reaction in which an acid and base react together to form a salt and water

38
Q

Define strong acid

A

An acid that completely dissociates in solution

39
Q

Define weak acid

A

an acid that partially dissociates in water

40
Q

Define Ka

A

The acid dissociation constant

41
Q

What happens when a metal and acid react

A

salt and hydrogen are formed

42
Q

What happens when a base and acid react

A

A salt and water formed

43
Q

hat happens when a carbonate and acid react

A

salt water and carbon dioxide formed

44
Q

What is the ionic equation for the reaction between an acid and carbonate

A

2H+ +CO3 2- –> CO2 +H20

45
Q

What is the ionic equation for the reaction of alkali and acid

A

H+ +OH- –> H20

46
Q

what is the ionic equation for the reaction of an acid and base (MgO)

A

2H+ +MgO –> Mg2+ H20

47
Q

What is the equation for Ka

A

[H+][OH-] / [HOH]

48
Q

What are the units of Ka

A

moldm-3

49
Q

Describe the relation between pKa and pH

A

The smaller the pKa value the stronger the acid

50
Q

How do you turn pKa into Ka

A

10**-pKa

51
Q

How do you find the H+ ion concentration from pH

A

10**-pH

52
Q

How do you find the pH from [H+]

A

-log([H+])

53
Q

What do you assume when calculating the pH of a strong acid

A

That the monobasic acid has virtually complete dissociation in water so the [H+] ion concentration is equal to the concentration of the acid

54
Q

How do you calculate the pH of a strong acid

A

-log(H+)
H+ = HOH

55
Q

What do we assume when calculating the pH of a weak acid

A

that the concentration of the acid at equilibrium is the same as the concentration of it at the start
That the concentration of H+ and OH- is equal

56
Q

How do you calculate the pH of a weak acid

A

Ka = [H+]**2 / [HOH]
[H+] = square root of Ka * HOH
pH = -log ([H+]

57
Q

What is Kw

A

The ionic product of water

58
Q

What is the value of Kw

A

at room temperature and pressure it is 1*10**-14

59
Q

What is the equation of Kw

A

Kw =[H+][OH-]

60
Q

Explain how water acts as an acid and base

A

This is because it can donate a proton like an acid (H20 ->H+ +OH-)

It can also accept a proton like a base (H20 + H+ -> H3O+)

61
Q

How do you calculate the pH of strong bases

A

[H+] = Kw / [OH-]
pH = -log [H+]

62
Q

What do we assume when calculating the pH of strong bases

A

That there is complete dissociation

63
Q

Define a buffer solution

A

A mixture that minimises pH changes on addition of small amounts of acid or base

64
Q

What is a buffer solution a mixture of

A

A weak acid and its conjugate base

65
Q

Describe how a solution can act as a buffer

A

The weak acid dissociates partially whereas the salt dissociates completely generating the conjugate base
The remaining mixture contains high concentrations of the undissociated acid and its conjugate base
The high concentrations of the conjugate base push the concentration of the conjugate base pushes the equilibrium to the left so the concentration of H+ ions is very smal

66
Q

How does a buffer act to control pH

A

The weak acid removes added alkali and the conjugate base removes added acid

67
Q

Describe how equilibrium shifts in a buffer solution when acid is added

A

The [H+] is increases and the conjugate base reacts with the H+ ions the equilibrium shifts to the left removing most of the H+ ions

68
Q

Describe how equilibrium shifts when alkali is added in a buffer solution

A

The small concentration of H+ ions reacts with the OH- ions
The weak acid dissociates shifting the equilibrium to the right to restore most of the H+ ions that have reacted

69
Q

define equivalence point

A

point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
centre of vertical section on curve

70
Q

Define end point

A

in a titration where the concentrations of weak acid and conjugate base forms of the indicator are equal
vertical section of the graph

71
Q

Describe how you would use a pH probe

A

calibrate with buffers such as pH 7 and rinse with distilled water and dry before use
place it in the storage solution when finished

72
Q

What happens to the equilibrium of the indicator in a low pH

A

equilibrium is pushed left and is colour 1

73
Q

What happens to the equilibrium of the indicator in a high pH

A

equilibrium is pushed right and is now colour 2

74
Q

Describe the colours of methyl orange in a reaction

A

red in a weak acid and yellow in its conjugate base and orange at its end point

75
Q

How would you pick an indicator for a titration

A

match equivalence point to indicator end point

76
Q

Describe the colours of phenolphthalein during a reaction

A

colourless at low pH and purple at a high pH

77
Q

What indicator would be suitable for a strong acid and base titration

A

either indicator can be used as both indicators have end points that lie within the vertical sections of the graph

78
Q

What indicator would be suitable for a strong acid-weak base titration

A

vertical section of the graph covers a smaller change in pH and only methyl orange can be used as it has an end point that falls within the range unlike phenolphthalein

A level chemistry (14 decks)

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