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Edexcel A Level Chemistry - 2021 MMS EXAMS > ✅16 - Kinetics II > Flashcards

✅16 - Kinetics II Flashcards

1
Q

What does rate of reaction tell you?

A

How fast reactants are converted to products

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2
Q

How is rate calculated?

A

Change in concentration of products/time

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3
Q

How can rate of reaction be determined experimentally?

A 
Gas volume
Loss of mass
Colour change
Change in pH
Titration
Electrical conductivity
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4
Q

How can gas volume be used to determine rate of reaction?

A

It can be collected in a syringe and the amount recorded at set intervals, and the ideal gas equation used to work out moles and then molar ratio

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5
Q

How can loss of mas be used to determine rate of reaction?

A

If a gas is given off, the system will lose mass, measured at regular intervals with a balance

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6
Q

How can colour change be used to determine rate of reaction?

A

Can be tracked with a colorimeter and a calibration curve plotted

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7
Q

How can change in pH be used to determine rate fo reaction?

A

If a reaction produces or used up H+, pH can be measured to determine the change in H+ concentration

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8
Q

How can titration be used to determine rate of reaction?

A

Small samples can be taken at regular intervals and titrated against a standard solution, change in concentration over time

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9
Q

How can electrical conductivity be used to determine rate of reaction?

A

If the number of ions changes, so will the conductivity

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10
Q

What is the rate constant?

A

K

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11
Q

What does the value of k change with?

A

Temperature

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12
Q

What do orders tell you?

A

How a reactant’s concentration affects the rate

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13
Q

How can orders of reaction be calculated?

A

From experimental data

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14
Q

What is the overall rider of a reaction?

A

The sum of all the orders of reaction of the reactants

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15
Q

What does a zero order concentration-time graph look like?

A

Straight line, top to bottom of Y axis

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16
Q

What does a zero-order rate-concentration graph look like?

A

Horizontal line

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17
Q

What does a first order concentration-time graph look like?

A

Curve, top to bottom

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18
Q

What does a first order rate-concentration graph look like?

A

Directly proportional

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19
Q

What does a second order concentration-time graph look like?

A

Steep curve, top to bottom

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20
Q

What does a second order rate-concentration time graph look like?

A

Curve, bottom to top

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21
Q

What is half life?

A

The time taken for half the reactant to be used up

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22
Q

How can orders of reaction be worked out?

A

Using the initial rates method

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23
Q

What is an example of the initial rates method?

A

A clock reaction

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24
Q

How is an initial rates method carried out?

A

Carrying out separate experiments using different initial concentrations of one reactant, then seeing how the change in Italy concentrations affects the rate

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25
Q

What is done in a clock reaction?

A

You measure the time taken or a set amount of product to form and how it changes as the concentrations vary

26
Q

What assumptions are made in clock reactions?

A

The concentration of arch reactant doesn’t change significantly over th period of the reaction
The temperature stays constant
When the end point is seen, the reaction has not proceeded too far

27
Q

What happens at the end of a clock reaction?

A

There’s an easily observable end point as there is a sudden increase in the concentration of a product as the limiting reactant is used up

28
Q

What is an example of a clock reaction?

A

The iodine clock reaction

29
Q

What is the reaction that occurs in the iodine clock?

A

H2O2 + 2I- + 2H+ ——> 2H2O + I2

30
Q

What is the indicator used?

A

Starch

31
Q

Why is sodium thiosulfate added to the mixture?

A

To react instantaneously with any iodine that forms

32
Q

What happens when the thiosulfate is used up?

A

The iodine becomes obvious with the indicator as it is allowed to form ithout reacting with the thiosulfate

33
Q

Which reactant’s concentrations are varied?

A

The iodide or hydrogen peroxide

34
Q

What is an example of a continuous monitoring method?

A

Titrations the reaction between iodine and propanone

35
Q

What is the equation for the reaction between iodine and propanone?

A

CH3COCH3 + I2 —H+—> CH3COCH2I + H+ + I-

36
Q

Why is sodium hydrogencarbnate added to samples of iodine-propanone before titrating?

A

To stop the reaction by neutralising the acid

37
Q

What do rate equations link?

A

Rate of reaction and reactant concentrations

38
Q

What is a rate equation?

A

Rate = k[A]^m [B]^n

39
Q

The bigger k is…

A

…the faster the reaction

40
Q

What can the rate constant be calculated from?

A

The orders and rate of reaction

41
Q

How can k be calculated?

A

Rate of reaction / concentrations and orders

42
Q

What is the rate determining step?

A

The slowest step in a multi-step reaction

43
Q

What does it indicate if a reactant appears in the rate equation?

A

That it features in the rate determining step

44
Q

What is the order of reaction with respect to a reactant?

A

Shows the number of molecules of that reactant that are involved in or before the rate determining step

45
Q

What can halogenoalkanes be hydrolysed by?

A

Hydroxide ions

46
Q

What do halogenoalkanes undergo?

A

Nucleophillic substitution

47
Q

By what mechanism are primary halogenoalkanes hydrolysed?

A

SN2

48
Q

By what mechanism are tertiary halogenoalkanes hydrolysed?

A

SN1

49
Q

What does an SN2 reaction include?

A

A transition state

50
Q

What does an SN1 reaction include?

A

An intermediate carbocation

51
Q

By what mechanism do secondary halogenoalkanes react?

A

SN1 or SN2

52
Q

What is the Arrhenius equation?

A

k = Ae^(-Ea/RT)

53
Q

What is the relationship between activation energy and k?

A

As Ea gets bigger, k gets smaller

54
Q

What is the relationship between k and temperature?

A

As temperature increases, so does k

55
Q

What is the gradient of an Arrhenius graph?

A

-Ea/R

56
Q

How can you find the activation energy from the Arrhenius graph?

A

By multiplying the gradient by R

57
Q

What are homogeneous catalysts?

A

In the same state as the reactant

58
Q

What are heterogeneous catalysts?

A

In a different physical state to the reactants

59
Q

How do solid heterogeneous catalysts work?

A

They provide a surface for the reaction to take place on, usually as a fine mesh or powder to increase surface area

60
Q

What is a benefit of heterogeneous catalysts?

A

They can be easily separated from the products and leftover reactants

61
Q

How can a heterogeneous catalyst be poisoned?

A

When a substance clings t the surface more strongly than the reactant does, preventing a catalyst from getting involved in the reaction

Edexcel A Level Chemistry - 2021 MMS EXAMS (19 decks)

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