Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry A - Level > Topic 16 - Kinetics II > Flashcards

Topic 16 - Kinetics II Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What is one graph that you can plot to determine the rate of reaction of a reaction?

A

Concentration - time graph

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do you determine the rate of reaction from a concentration-time graph?

A

Take the gradient at that point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

State the rate of reaction equation?

A

ROR = Change in concentration/ time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the units for rate of reaction?

A

moldm^-3s^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why do we not always measure concentration of a substance when determining the rate of a reaction?

A

As, practically speaking, it may be easier to measure a quantity rather than a concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What do you need to do if you have measured a quantity rather than a concentration when conducting a rate of reaction experiment?

A

Convert the quantity into a number which is proportional to the concentration of the substance concerned

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the 6 experimental methods you can use to measure reaction rates?

A
  • Measuring a volume of gas
  • Measuring loss of mass
  • Titration
  • Colorimetry
  • pH measurements
  • Conductivity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When is the rate of reaction method ‘measuring volume of a gas’ used and what are some notes on this method?

A

Used:
- If product is a gas

Notes:
- A gas syringe can be used to collect the volume

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When is the rate of reaction method ‘measuring loss of mass’ used and what are some notes on this method?

A

Used:
- If product is a gas

Notes:
- An open reaction vessel is placed on a balance and the change in mass is measured over time
- The change in mass may be small if the gas has a low density (e.g H2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

When is the rate of reaction method Titration used and what are some notes on this method?

A

Used:
- If the reactant or product is an acid or alkali which can be neutralised
- If iodine is a reactant or product then sodium thiosulphate is used in the titration

Notes:
- A sample of known volume is removed from the reaction mixture at a certain time
- The sample is quenched (stopped/slowed)
- The sample is titrated with an appropriate reagant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When is the rate of reaction method Colorimetry used and what are some notes on this method?

A

Used:
- If there is a significant change in the colour of a liquid or solution
- If a ppt. is formed

Notes:
- The colorimeter detects the amount of light which passes through the reaction vessel (how much is absorbed) The absorbance is then compared to known absorbances for known concentrations of the same substance using a calibration curve
- If a darker solution/ppt. is formed then less light will be detected as the concentration of the product increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When is the rate of reaction method ‘pH measurements’ used and what are some notes on this method?

A

Used:
- If there is a change in pH (either an acid or alkali is consumed or produced)

Notes:
- A pH probe can be used to monitor the pH of a mixture as the reaction proceeds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are 3 ways that you quench a titration?

A
  • Cooled
  • Diluted
  • Another substance is added to stop the reaction proceeding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When is the rate of reaction method using conductivity used and what are some notes on this method?

A

Used:
- When there is a change in the no. of ions as the reaction proceeds, therefore, its conductivity

Notes:
- The reaction mixture you are testing is in a beaker -> platinum electrodes are placed into the beaker and these are connected to a conductivity meter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Write the rate equation for the reaction aA + bB -> products?

A

Rate = k[A]^x[B]^y

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Do the reacting moles tell you anything about the rate equation?

A

No

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the only way you can find out the orders with respect to each of your reactants?

A

Practically

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the definition of the rate constant, k?

A

A constant of proportionality that connects the rate of reaction with the reactant concentrations, it is a constant for a particular temperature and only changes if the temperature is changed or a catalyst is added

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What do the powers in a rate equation tell us?

A

These are the orders of the reaction -> They describe how the concentration of each reactant affects the rate of reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What will the orders with respect to reactants usually be one of?

A

0, 1 or 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

If the order to reactant [A] is 0, then what will its effect on the rate be and how will it appear in the rate equation?

A
  • Rate is not affected by [A]
  • It will not appear in the rate equation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

If the order to reactant [A] is 1, then what will its effect on the rate be and how will it appear in the rate equation?

A
  • Rate is proportional to [A] e.g if [A] was doubled then the reaction rate would double etc.
  • Appears as [A] in the rate equation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

If the order to reactant [A] is 2, then what will its effect on the rate be and how will it appear in the rate equation?

A
  • Rate is proportional to [A]^2 e.g if [A] was doubled then the reaction rate would quadruple
  • Appears as [A]^2 in the rate equation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

If rate = k[A] what are the units of the rate constant?

A

s^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

If rate = k what are the units of the rate constant?

A

moldm^-3s^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

If rate = k[A]^2[C] what are the units of the rate constant?

A

dm^6mol^-2s^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What part of the rate equation does changing the temperature or adding a catalyst change?

A

rate constant, k

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the effect on the ROR and the rate constant, k, when a reactant concentration is increased?

A
  • ROR increases
  • k remains the same
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the effect on the ROR and the rate constant, k, when the temperature is increased?

A
  • ROR increases
  • Increased value of rate constant, k
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the effect on the ROR and the rate constant, k, when a catalyst is added?

A
  • ROR increases
  • Increased value of rate constant, k
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Describe the shape of a concentration-time graph for a 0 order reactant

A

Concentration of reactant is inversely proportional to time, therefore graph is a negative straight line

32
Q

Describe the shape of a concentration-time graph for a 1st order reactant

A

Concentration decreases withe a constant half life, therefore the graph line is curved

33
Q

Describe the shape of a concentration-time graph for a 2nd order reactant

A

Concentration decreases exponentially, therefore graph line is curved even more so than for 1st order graphs

34
Q

What is the definition of half life for a reactant?

A

The time taken for the reactant concentration to reduce by half

35
Q

What is another graph that can be drawn when investigating reaction rates?

A

rate-concentration graph

36
Q

Describe the shape of a rate-concentration graph for a 0 order reactant?

A

Rate = k
- Straight horizontal line through value k

37
Q

How do you go from a concentration-time graph to a rate-concentration graph?

A
  • Find the gradient on the concentration-time graph at multiple time points -> this is the rate at these concentrations
  • Plot a graph of rate against concentration for the values you have chosen
38
Q

What do concentration-time and rate-concentration graph show you?

A

The order with respect to THAT SPECIFIC REACTANT

39
Q

Describe the shape of a rate-concentration graph for a 1st order reactant?

A

Rate = k[A]
- Rate and [A] are directly proportional
- y=x line going through the origin

40
Q

Describe the shape of a rate-concentration graph for a 2nd order reactant?

A

Rate = k[A]^2
- Rate is directly proportional to [A]^2
- Exponentially increasing line that begins at the origin

41
Q

In what instance would you have to plot another graph in order to find the order with respect to a reactant?

A

If you have plotted a concentration-time graph it can be hard to distinguish between a first order and second order graph

42
Q

What are the two ways that you can determine reacting orders of a reaction?

A
  • Plot graphs and use known shapes to determine the order
  • Changing the concentration of reactants and seeing how that affects initial ROR
43
Q

What are the 2 ways that you can find the initial ROR?

A
  • Find the gradient at time = 0 on a concentration-time graph
  • Time how long it takes for a certain amount of product to be made and calculating 1/time as the initial rate (a clock reaction)
44
Q

When trying to determine the order with respect to each of your reactants in a reaction, why do you need to add water as you change the concentrations of your reactants?

A

To ensure that the same total volume is present for each mixture, therefore, the concentration of each reactant is proportional to the volume of that reactant added

45
Q

What is the definition of an autocatalysis reaction?

A

This is when the catalyst for the reaction is made as a product of the reaction

46
Q

What element of a reaction do rate equations tell us about?

A

The mechanism of the reaction

47
Q

What does the overall rate of a reaction depend on?

A

The rate of the slowest step

48
Q

What is the slowest step known as?

A

The rate determining step

49
Q

What species will appear in the rate equation?

A

Species that are part of the reaction mechanism before or during the rate determining step

50
Q

What species wont appear in the rate equation?

A

Species that are part of the reaction mechanism after the rate determining step

51
Q

What will the rate equation look like for the Sn1 mechanism for the reaction from halogenoalkane -> alcohol?

A

k[halogenoalkane]

52
Q

What will the rate equation look like for the Sn2 mechanism for the reaction from halogenoalkane -> alcohol?

A

k[halogenoalkane][OH-]

53
Q

Describe the reaction profile for the Sn1 mechanism/catalysed reactions?

A
  • Curve going up and down stopping above the initial line of reactants
  • Line drawn going across representing the intermediate
  • Curve going up and down as normal to final products
54
Q

What is a reason why the initial rate of reaction might be very slow?

A

The two species you are reacting might have the same charge, therefore repelling one another

55
Q

Describe the rate of an autocatalysis reaction over time?

A

Initially the reaction will be slow, however, as the products are formed, one of which being the catalyst, the reaction will speed up exponentially.

56
Q

Describe what a rate-time graph looks like for an autocatalysis reaction?

A

shallow gradient -> steep gradient -> shallow gradient

57
Q

What is the definition of a reaction mechanism?

A

A sequence of elementary steps that leads to the formation of the products, the sum of which gives the overall balanced equation of the reaction

58
Q

When there is one species in an elementary step of a reaction mechanism what is the molecularity of this step?

A

unimolecular

59
Q

When there are two species in an elementary step of a reaction mechanism what is the molecularity of this step?

A

bimolecular

60
Q

When there are three species in an elementary step of a reaction mechanism what is the molecularity of this step?

A

termolecular

61
Q

When given a multi step mechanism for a reaction how do you know which species are intermediates/catalysts?

A

Catalysts - will be used up early on and reformed later
Intermediates - will be produced but then used up so will not appear in the overall reaction equation

62
Q

Can catalysts appear in rate laws/expressions?

A

yes

63
Q

Can intermediates appear in rate laws/expressions?

A

no

64
Q

Can catalysts appear in the overall reaction equation?

A

no

65
Q

If one of the elementary steps before the rds is an equilibrium containing an intermediate e.g A <=> B, how would you remove the intermediate from the rate equation?

A

Kc = [B]/[A]
[B] = Kc[A]

sub the above into the rate equation

66
Q

Why can we say that rate is proportional to 1/t and initial rate = 1/t in clock reactions?

A
  • You choose a fixed concentration of products to be formed for each run of the reaction
  • As rate = conc/time but the concentration is constant for each run you can say that initial rate = 1/t
67
Q

Why is the statement initial rate = 1/t an approximation?

A
  • Initial rate is the gradient from a conc-time graph when time equals 0
  • The initial straight line portion of the graph will correspond to this rate
  • However, if the concentration we have chosen is not in this portion of the graph it may give us a rate that is slower than the initial rate
68
Q

What are the clock reactions that you need to be able to recognise?

A
  • The sulfur clock reaction
  • The iodine clock reaction
  • The bromine clock reaction
  • Iodide ions an peroxodisulfate(VI) ions
69
Q

Sulfur clock reaction:
- What happens?
- Equation
- Why is the initial rate proportional to 1/t for this reaction?

A
  1. Sodium thiosulfate reacts with dilute hydrochloric acid producing a ppt. of sulfur. As the sulfur is formed it blocks the X drawn on a piece of card below the contents of the reaction mixture. Different volumes of thiosulfate are added to a beaker and made up to a constant volume with water for each run.
  2. S2O3(2-) aq + 2H(+) aq -> S s + SO2 g + H2O l
  3. For each run you stop the clock when the X is obscured, therefore when the same amount of sulfur is produced each time
70
Q

Iodine clock reaction:
- What happens?
- Equation
- Why is the initial rate proportional to 1/t for this reaction?

A
  1. The oxidation of iodide, I- ions by hydrogen peroxide, H2O2 in acid solution.
    - For each run, different volumes of hydrogen peroxide solution are added to a beaker and made up to constant volume with water. A few drops of starch solution are also added to this beaker.
    - In a separate beaker, for each run, a specific volume of KI solution and a SPECIFIC VOLUME OF DILUTE SODIUM THIOSULFATE ARE MIXED (sodium thiosulfate is a reducing agent)
    - The contents are mixed and the time taken for the solution to turn blue is measured
  2. MAIN EQUATION: H2O2 aq + 2I(-) + 2H (+) -> 2H2O l + I2 aq

I2 aq + 2S2O3(2-) aq -> 2I- aq + S4O6(2-) aq

  • When iodine is formed in the main reaction it immediately reacts with the thiosulfate ions present in solution which reduce the iodine back to iodide
  • Once the constant volume of thiosulfate ions per run is used up the I2 produced from the main reaction reacts with the starch indicator giving a blue/black colour
  1. For each run you are using a fixed moles of S2O3(2-) ions which will react with a fixed moles of Iodine in every run. Therefore, in every run you are noting the time that the fixed moles of iodine has been produced as this is when the S2O3(2-) moles has been used up and so the iodine produced will now start reacting with the starch to produce the blue/black colour.
71
Q

Bromine clock reaction:
- What happens?
- Equation
- Why is the initial rate proportional to 1/t for this reaction?

A
  1. The reaction between bromide ions, Br-, and bromate (V) ions, BrO3(-) in acid solution.
    - The reaction is monitored in the presence of a small amount of phenol and methyl red
    - The indicator is initially pink due to the H+ ions present in solution
    - Time how long it takes for the methyl red to be bleached from pink to colourless
  2. MAIN EQUATION: 5Br(-) aq + BrO3(-) aq + 6H+ aq -> 3Br2 aq + 3H2O l

3Br2 aq + C6H5OH aq -> C6H2OHBr3 aq + 3H+ aq + 3Br- aq

  • When bromine is formed in the main reaction it immediately reacts with the phenol present in solution which reduces the bromine back to bromide
  • Once the constant volume of phenol is used up (same for each run) the Br2 reacts with the methyl red indicator, bleaching it to colourless
  1. For each run you are adding a fixed no. of moles of phenol that react with a fixed number of moles of Br2. Therefore, in every run you are always measuring the time taken for the fixed number of moles of Br2 to be produced as this is when the Br2 no longer reacts with phenol and therefore, bleaches methyl red -> colourless.
72
Q

Iodide ions and S2O8(2-) ions reaction:
- What happens?
- Equation
- Why is the initial rate proportional to 1/t for this reaction?

A

1.
- Measure a constant volume of KI for each run alongside a CONSTANT VOLUME OF SODIUM THIOSULFATE FOR EACH RUN in to a beaker. Add a few drops of starch to this beaker.
- Measure different volumes of sodium peroxodisulfate solution for each run made up to a constant volume with water
- Pour the mixtures into one another and time how long it takes for the solution to go blue/back

  1. MAIN EQUATION: S2O8(2-) + 2I(-) -> 2SO4(2-) + I2

2S2O3(2-) +I2 -> S4O6(2-) +2I(-)

  • When iodine is formed in the main reaction it immediately reacts with the thiosulfate ions present in solution which reduce the iodine back to iodide
  • Once the constant volume of thiosulfate ions per run is used up the I2 produced from the main reaction reacts with the starch indicator giving a blue/black colour
  1. For each run you are using a fixed moles of S2O3(2-) ions which will react with a fixed moles of Iodine in every run. Therefore, in every run you are noting the time that the fixed moles of iodine has been produced as this is when the S2O3(2-) moles has been used up and so the iodine produced will now start reacting with the starch to produce the blue/black colour.
73
Q

What is the name of the equation that shows you how the rate constant, k, changes with respect to altering the temperature and/or adding a catalyst?

A

The Arrhenius Equation

74
Q

What is the Arrhenius equation?

A

k = Ae^(-Ea/RT)

A = Arrenhius constant that incorporates the effect of collision frequency and orientation

75
Q

What is the way that you use the Arrenhius equation to plot a graph?

A

ln(k/rate - they are interchangable) = ln(A) -Ea/RT

  • This is a straight line graph
76
Q

What are the units of activation energy?

A

kJmol^-1

77
Q

What are the two factors required for a collision to be successful?

A
  • The E >= Ea
  • The particles must be in the correct orientation relative to each other (steric factor)

Chemistry A - Level (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions