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Chemistry > 3 + 4 Rates of Reaction > Flashcards

3 + 4 Rates of Reaction Flashcards

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1
Q

Define ‘rate of reaction.’

A

the change in concentration of a species per unit of time

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2
Q

State the two ways rate of reaction can be expressed for the single step reaction A → B.

A

Rate = -Δ[A] / Δt
OR
Rate = Δ[B] / Δt

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3
Q

State the units for any rate of reaction.

A

mol L-1 s-1 (or mol/l/s)

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4
Q

How can the rate of a reaction be calculated directly from a concentration-time graph?

A

by drawing a tangent and then calculating the gradient of it

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5
Q

When do reactions occur and which two conditions must be met in order for a reaction to occur?

A

reactions occur when particles collide
particles must possess at least a minimum amount of energy
particles must approach each other in a certain, relative orientation

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6
Q

Which two factors influence the reaction rate?

A
  1. the overall number of collisions occurring

2. the number of particles with enough energy to react

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7
Q

Define ‘activation energy, Ea.’

A

the minimum amount of energy required to initiate a chemical reaction

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8
Q

Define ‘transition state.’

A

highest energy point in the reaction

the configuration of the atoms at the time of the collision

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9
Q

On the following graph, label (1-4) reactants, products, ΔG and the transition state of the reaction.

A

1 - reactants
2 - products
3 - transition state
4 - ΔG

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10
Q

Draw out a normal Boltzmann distribution for a reaction.

A

see document

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11
Q

Explain how increasing temperature increases the rate of reaction.

A

particle speed increases so collisions are more frequent

particles have more energy, so can overcome the energy barrier

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12
Q

Draw out a normal Boltzmann distribution for a reaction and on the same axes draw another showing the effect of temperature on a rate of reaction.

A

see document

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13
Q

Explain how adding a catalyst increases the rate of reaction.

A

works by providing an alternative reaction pathway with a lower Ea
more particles now have the energy to react

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14
Q

Draw out a normal Boltzmann distribution for a reaction and on the same axes draw another showing the effect of a catalyst on a rate of reaction.

A

see document

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15
Q

Explain how increasing surface area of solid reagents/heterogeneous catalysts increases the rate of a reaction.

A

increases chances of a collision - more particles are exposed
powdered solids react quicker than large lumps

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16
Q

Explain how increasing the pressure of a gas increases the rate of a reaction.

A

forces gas particles closer together increasing the frequency of collision so the reaction rate increases

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17
Q

Explain how increasing the concentration of liquids increases the rate of a reaction.

A

the larger number of particles, therefore, more collisions

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18
Q

What does the rate of any reaction mainly depend on?

A

concentration of reactants

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19
Q

For the reaction equation, wA + xB → yC + zD, what is the general form of a rate equation?

A

Rate = k [A]^m [B]^n
where k = rate constant
m,n = reaction orders w.r.t to those reagents
m+n = overall reaction order

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20
Q

What is the only way a reaction order can be found?

A

by experiment

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21
Q

What is meant by a ‘zero-order’ of reaction?

A

where the rate is independent of the concentration of reactant
Rate = k
Overall order = 0
The rate does not change

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22
Q

What does a ‘zero-order’ reaction depend on?

A

depends on a catalytic bottleneck (catalyst)

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23
Q

What is meant by a ‘first-order’ of reaction?

A

where the rate is proportional to the concentration of a single reactant raised to the first (n^1) power
Rate = [A] k
overall reaction order = 1

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24
Q

How does integrated rate law describe the concentration of a reactant as a function of time?

A

ln[A]t = -kt + ln[A]0

y = mx+ b

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25
Q

Define ‘half-life.’

A

the time taken for the concentration of a reactant to drop to half of its initial value

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26
Q

What is half-life for a ‘first-order’ reaction?

A

half-life is constant; depends on the rate constant (k) and the concentration of reactant

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27
Q

Where is constant half-life usually seen?

A

In the half-life of radioactive isotopes i.e. medicine, nuclear energy etc…

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28
Q

Draw a graph to show how half-life varies during a ‘first-order’ reaction.

A

see document

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29
Q

State the formula that can be used to calculate k (rate constant) for a first-order of reaction using half-life (t1/2).

A

k = ln(2) / t1/2

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30
Q

What is meant by a ‘second-order’ of reaction?

A

has a rate law with the sum of exponents equal to 2
overall reaction order is 2
Rate = k[A][B] OR Rate = k[A]^2
m + n = 2 OR m = 2

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31
Q

What is meant by a ‘pseudo’ first-order reaction?

A

A reaction that is not a naturally ‘first-order’ reaction but instead depends on the variation of two reagents
pseudo = fake

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32
Q

Describe the shape of each of the following order rate-concentration graphs in terms of half-life:

a) Second-order reaction
b) First-order reaction
c) Zero-order reaction

A

a) the curve declines steeply at first then levels out. Half-life increases as the reaction progresses
b) A slightly-sloping curve which drops with a constant half-life
c) a straight line showing a constant decline in concentration. Half-life decreases as the reaction progresses

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33
Q

Describe the relationship between each of the following order rates and concentrations:

a) Second-order reaction
b) First-order reaction
c) Zero-order reaction

A

a) the rate is proportional to the square of the concentration ([X]^2 x k) so you get a curved line
b) the rate is proportional to the concentration ([X] x k)
the gradient of the line equals the rate constant for the reaction
c) the rate does not depend on the concentration
the line is parallel to the x-axis ([X]^0 x k)

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34
Q

On the following rate-concentration graphs (see document), identify the order of reaction for lines (1-3).

A

1 - first-order
2 - second-order
3 - zero-oder

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35
Q

Using the initial rates table on the document, determine the order with respect to reactants A and B.

A 
For [A]:
Initial conc → 0.5M/0.25M = 2
Rate → 0.0052/0.0013 = 4
So, when [A] x2
Rate x 4
therefore, second-order w.r.t. [A]
For [B]:
Initial conc → 0.04M/0.02M = 2
Rate → 0.0026/0.0013 = 2
So, when [B] x2
Rate x 2
therefore, first-order w.r.t. [A]
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36
Q

Complete the flow chart about the order of reaction starting with the following question following both answers yes and no:

Plot [A] Vs t
Is graph linear?
Yes OR No

A

See document

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37
Q

What do many reactions consist of?

A

a series of separate stages

each step has its own rate and rate constant

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38
Q

What governs the overall rate of a multi-step reaction?

A

the (slowest) rate-determining step

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39
Q

What does the rate equation of a reaction only include?

A

the molecules involved in the rate-determining-step (RDS)

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40
Q

Define ‘molecularity.’

A

the number of individual molecules of the reacting species taking part in the rate determining step of the reaction

41
Q

State the general rate determining step and rate law for a unimolecular reaction.

A

RDS: A →

Rate law: Rate = k [A]

42
Q

State the general rate determining step and rate law for a bimolecular reaction.

A

RDS: A + A →
OR A + B →
Rate law: Rate = k [A]^2
OR Rate = k[A][B]

43
Q

State the general rate determining step and rate law for a trimolecular reaction.

A 
RDS: A + A + A → 
OR A + A + B →
OR A + B + C →
Rate law: Rate = k [A]^3 
OR  Rate = k[A]^2[B]
OR  Rate = k[A][B][C]
44
Q

Why may a reaction give different products?

A

depending on conditions

45
Q

What is a fast reaction referred to as?

A

low Ea

and kinetically favourable

46
Q

Thermodynamically, when is a reaction favourable?

A

when it leaves a system in a more stable state

47
Q

Fill in the labels 1-8 on the graph on kinetic and thermodynamic control (see document).

A 
1 – kinetic control
2 – thermodynamic control 
3 – transition state 
4 – intermediate 
5 – ΔG
6 – starting materials 
7 – kinetic products 
8 – thermodynamic products
48
Q

Which 4 things does a catalyst do for a reaction?

A

reduces the Ea of a reaction
brings reactants closer together
weaken bonds in reactants
stabilise the transition state

49
Q

Draw 2 enthalpy profile diagrams for a reaction with and without a catalyst. For each diagram label Ea and ΔH.

A

See document

50
Q

Define ‘enzyme.’

A

a biological catalyst

51
Q

What type of proteins are enzymes and what do they catalyse?

A

mostly globular proteins

catalyse one reaction/type of reaction

52
Q

What do ‘oxidoreductases’ catalyse?

A

reduction (add hydrogen atoms or electrons)

53
Q

What do ‘transferases’ catalyse?

A

transfer groups from one molecule to another

54
Q

What do ‘hydrolases’ catalyse?

A

break bonds by adding water

55
Q

What do ‘lyases’ catalyse?

A

(deXases); remove a functional group from a molecule i.e. decarboxylases/dehydrogenases

56
Q

What do ‘isomerases’ catalyse?

A

switch molecules between isomers

57
Q

What do the names of enzymes tend to depend on?

A

the substrate/reaction catalysed

58
Q

Name an example of a hydrolase enzyme and the reaction it catalyses drawing out the molecules too.

A

lactose → galactose
lactase

see document for diagrams

59
Q

Briefly explain the ‘lock-and-key’ model of enzyme action.

A

both enzyme and substrate have a unique, fixed shape

only one substrate (key) can fit into the enzyme’s active site (lock)

60
Q

What does the ‘lock-and-key’ model of enzyme action not explain?

A

all experimental observations

61
Q

Briefly explain the ‘induced-fit’ model of enzyme action.

A

substrate enters active site of the enzyme
forms an E-S complex and enzyme changes shape slightly as the substrate binds
an E-P complex is formed
products leave the active site of the enzyme

62
Q

State the 4 non-specific factors influencing enzyme activity.

A

temperature
pH
kinetics
concentration

63
Q

State the 3 specific factors influencing enzyme activity.

A

cofactors
coenzymes
inhibitors

64
Q

Fill in the processes 1-2 on the diagram of an enzyme.

A

1 - denaturation

2 - renaturation

65
Q

What temperature do all enzymes have and what happens to the enzyme above it? Provide an example for each.

A

an ‘optimum’ temperature i.e. 37°C in humans

enzyme becomes denatured above it i.e. fever, pyrexia does this

66
Q

Give an example of when the effect of temperature on enzymes is exploited.

A

In the polymerase chain reaction (PCR)

i.e. Taq polymerase, primer etc…

67
Q

Describe the effect of pH on enzymes.

A

each enzyme has a different optimum pH
affects protonation of enzyme and active site
conformation and stability of enzyme

68
Q

Which features do concentrations of enzyme/substrate affect?

A

the Km and Vmax of enzymes

69
Q

What is the ‘michaelis-menten’ equation and what is it used for?

A

V0 = Vmax[S]/{Km + [S]}

V0 - velocity or reaction rate
Vmax[S] - maximum velocity or maximal reaction rate
Km - Michaelis constant (where concentration is working at half of Vmax)
[S] - Substrate concentration

reflection of the affinity of the enzyme for its substrate

70
Q

Explain the significance of Km in enzyme activity.

A

Small Km = strong E-S binding

Large Km = weak E-S binding, little activity at low concentrations of substrate

71
Q

What is Km is related to?

A

the rate constants for each step in the enzyme reaction

72
Q

Fill in labels 1-3 on the substrate concentration vs reaction rate graph on the document.

A

1 - Km
2 - Vmax
3 - 1/2Vmax

73
Q

Fill in labels 1-5 on the Lineweaver-Burke plot on the document.

A 
1 – Km/Vmax
2 – 1/Vi
3 – -1/Km
4 – 1/Vmax
5 – 1/[S]
74
Q

What do cofactors and coenzymes do?

A

Complete the structure of conjugated enzymes

75
Q

Briefly describe how enzymes are activated.

A

Apoenzyme becomes active by binding of coenzyme or cofactor to enzyme
Holoenzyme is formed when associated cofactor/coenzyme binds to the enzyme’s active site

76
Q

State 6 examples of cofactors/coenzymes.

A 
Zn^2+
Mg^2+
Vitamin B12
NAD(P)H
FAD+
Coenzyme A
77
Q

Identify the 4 cofactors/coenzyme structures on the document.

A

1 – Vitamin B12
2 – NAD(P)H
3 – Coenzyme A
4 – FAD+

78
Q

State the 5 ways non-specific enzyme inhibition/deactivation work.

A 
acids and bases 
temperature 
alcohol 
reducing agents 
heavy metals
79
Q

Define ‘competitive’ reversible inhibition.

A

bind to free enzyme only - usually in an active site

E + I ⇌ EI

80
Q

Define ‘irreversible’ enzyme inhibition.

A

bind so tightly to the enzyme they cannot be displaced

81
Q

How does irreversible enzyme inhibition work.

A

often form covalent bonds, modifying the structure and removing the activity of the enzyme active site

82
Q

Give 3 examples of irreversible enzyme inhibition.

A

aspirin
organophosphates
suicide inhibitors

83
Q

Identify each of the following irreversible enzyme inhibitors on the document.

A

1 – Aspirin
2 – catalytically inactive
3 – parathion
4 – Novichock agents

84
Q

Define ‘allosteric’ enzyme inhibition.

A

bind in a regulatory site, not an active site

85
Q

Give an example of allosteric enzyme inhibition.

A

strychrine

86
Q

Define ‘non-competitive’ enzyme inhibition.

A

bind free enzyme and enzyme-substrate complex equally well; don’t bind in exact site occupied by substrate
E + I → EI
and/or ES + I → ESI

87
Q

Define ‘uncompetitive’ enzyme inhibition.

A

bind the enzyme-substrate complex

ES + I → ESI

88
Q

Identify the types of enzyme inhibition labelled 1-3 in each diagram.

A

1 – competitive reversible
2 – allosteric
3 – uncompetitive/non competitive

89
Q

Beta-lactamases deactivate penicillin-type antibiotics by the mechanism shown below (see document). Clavulanic acid inhibits the deactivation of penicillin; its mechanism of action is shown below. What type of inhibitor is clavulanic acid?

A

A competitive inhibitor

90
Q

State the integrated rate law equation for a ‘zero order’ equation.

A

A0 – At = kt

91
Q

Rearrange “-d[A]/[A] = kdt” for the integrated rate law and state what form it holds.

A 
-d[At]/[A0] = kdt (divide by -d)
[A]t/[A]0 = -kt (apply logs)
ln{[A]t/[A]0} = –kt (apply log law)
ln[A]t – ln[A]0 = –kt  (+ln[A]0)
ln[A]t = –kt + ln[A]0
This corresponds to:
     y	  =  mx + b
92
Q

State the integrated rate law for:

a) a zero-order reaction
b) a first-order reaction
c) a second-order reaction

A

a) [A]t = -kt + [A]0
b) ln[A]t = -kt + ln[A]0
c) 1/[A]t = -kt + 1/[A]0

93
Q

For a first-order reaction, rearrange the integrated rate law for the formula to find k.

A 
ln[A]t                   = -kt    +    ln[A]0
ln½[A]0 – ln[A]0 = –kt½
ln(½)                    = –kt½
ln2                       = kt½ 
k                          = ln2/t½
94
Q

In what instance is a reaction a pseudo-first-order reaction?

A

when one reagent is present in very large excess

95
Q

Why is there two Ea values for an enzyme catalysed enthalpy diagram?

A

because there is a different intermediate product to get to before the product

96
Q

Describe the four main stages of PCR and how it exploits enzymes.

A

1) denature DNA and separate the two strands by heating to a high temperature (approx. 95°C)
2) anneal primer to join the two strands together
3) free nucleotides are left free to join as base-pairs again (elongation)
4) this results in the DNA splitting which is repeated until the DNA is amplified

97
Q

What is the role of Taq polymerase in PCR?

A

Taq polymerase (adapted for high temperatures) attaches nucleotides to a DNA template copying the DNA

98
Q

For each of the following types of enzyme inhibition, state, in very basic terms, how it works:

a) Competitive
b) Allosteric
c) Non-competitive
d) Uncompetitive

A

a) binds to same active site as enzyme
b) changes the shape of the enzyme’s active site by binding to a regulatory site
c) Has a different active site and results in a conformational change of substrate active site
d) binds to E-S complex to stop it from working

Chemistry (12 decks)

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