kinetics ii

Question 1

what is reaction rate ?

Answer 1

.measure of how fast a reaction takes place
.defined as the change in concentration of a reactant or product per unit time

Question 2

what is collision theory

Answer 2

.for particles to react they must collide with sufficient energy to react and at the correct orrientation
.the minimum energy particles need to react is called the activation energy

Question 3

describe Maxwell Boltzmann distribution

Answer 3

.particles in substance do not all have the same amount of energy
.energy of particles of gas is shown by a Maxwell Boltzmann distribution
.there are no particles with no energy
.area under curve represents total number of particles
.the peak of the curve gives the the energy that more particles have than any other energy
.number of particles on y axis energy on y axis

Question 4

what are the factors affecting rate

Answer 4

concentration of a solution, surface area of a solid, pressure of gases ,temperature, catalyst

Question 5

what affects does concentration have on the rate

Answer 5

.the higher the concentration the faster the reaction (unless that reagent is zero order). because particles are closer together and so there are more frequent and successful collisions

Question 6

what affects does surface area have on the rate

Answer 6

.the more pieces a solid is broken up to the bigger the surface area the greater the surface area the greater the rate of reaction, because there are more particles exposed at the surface that can be collided with and so there’s more frequent successful collisions

Question 7

what affect does pressure have on the rate

Answer 7

the higher the pressure the higher the rate, particles have more energy and so greater proportion of the collisions are successful the particles also move faster and so collisions are more frequent therefore there are more frequent successful collisions

Question 8

what affect does a catalyst have on the rate

Answer 8

a catalyst is a substance that increases the rate of a reaction but is not used up it provides alternative route /mechanism with a lower activation energy and therefore a greater proportion of the collisions are successful

Question 9

what is order of reaction

Answer 9

power to which the concentration of the reactant is raised in the rate equation.

Question 10

what is overall order of reaction

Answer 10

sum of the powers of the concentration terms in the rate equation.

Question 11

The only thing that affects the value of k (the rate constant) is ….

Answer 11

temperature

Question 12

what are the different ways to measure reaction rate

Answer 12

measuring gas volume
loss of mass
colour change/colorimetry
change in ph
titration
electrical conductivity

Question 13

how to measure reaction rate by gas volume

Answer 13

collect the gas given off in a gas syringe and record how how much there is at regular time interviews
you can then find out the concentration at each time point by using ideal gas equation

Question 14

how to measure reaction rate using loss of mass method

Answer 14

if gas is given off then mass is lost you can measure the mass remaining at regular time intervals with a balance
you can use moles equation to work out how much gas you have lost and therefore how many reactants is left

Question 15

how to measure rate of reaction using colour change method

Answer 15

you can track the colour change using a colorimeter which measure the absorbance, the more concentrated the colour the higher the absorbance

you can measure the change in absorbance by plotting a calibration curve a graph of known concentrations against absorbance

during the experiment take small sample from reaction solution at regular intervals and read the absorbance

use calibration curve to convert the absorbance at each time point into a concentration

Question 16

how to measure rate of reaction using ph method

Answer 16

if reaction produces or uses up H ions the pH of the solution will change so you could measure the pH at regualr time intervals and calculate the concentration of H

Question 17

how to measure rate of reaction using titration method

Answer 17

*take small samples of a reaction mixture at regular time intervals
*quench them
*titrate them using standard soloution
*the rate can be found from measuring the change in concentration of the products or reactant over time

Question 18

how to work out reaction rate from concentration time graph

Answer 18

the rate at any point in the reaction is given by the gradient at that point on the graph
if the graph is a curve you have to draw a tangent to the curve and find the gradient of that

Question 19

what does the order of reaction tell you

Answer 19

tells you how with respect to a certain reactant how the reactants concentration affects the rate

Question 20

you can only find the orders of reaction from

Answer 20

experiments

Question 21

for a concentration time graph what order is a straight line

Answer 21

zero order

Question 22

for concentration time graph what order is a curve and an even steeper curve

Answer 22

normal curve first order even steeper curve is second order

Question 23

for rate concentration graph what order is a straight horizontal line

Answer 23

zero order

Question 24

for rate concentration graph what order is a straight line through origin

Answer 24

first order

Question 25

for rate concentration graph what order is a curve through origin

Answer 25

second order

Question 26

what is the half life

Answer 26

half life is the time it takes for half or the reactants to be used up

Question 27

how do you work out half life from concentration time graph

Answer 27

plot concentration time graph then draw lines across from the y axis at points where the concentration has halved and read off time taken

Question 28

what are half lives useful for

Answer 28

identifying first order reactions without having to draw a rate concentration graph because half life is always constant for first order reactions

Question 29

initial rate method is used to work out?

Answer 29

orders of reactions

Question 30

initial rate of a reaction is the rate at ?

Answer 30

the start of the reaction time = 0

Question 31

how to do initial rates method?

Answer 31

*carry out separate experiments using different initial concentrations of one reactant *change concentration of only one reactant *then see how the change in in initial concentration affects the initial rates and work out order of each reactant *you can do this using continuous monitoring techniques and drawing concentration time graphs *by calculating the gradient at time=0 you can work out the initial rate

Question 32

a clock reaction is an example of a

Answer 32

initial rates method

Question 33

What is clock reaction

Answer 33

*clock reactions measure how long the time taken for amount of product to form Changes as you vary the concentration of one of the reactants

Question 34

assumptions of carrying a clock reaction

Answer 34

*concentration of each reactant doesn’t change significantly/concentration change of each reactant insignificant *the temperature stays constant *when the end point is seen the reaction has not gone too far

Question 35

describe iodine clock reaction

Answer 35

*A small amount of sodium thiosulfate solution and starch are added to an excess of hydrogen peroxide and iodide ions *sodium thiosulfate reacts instantaneously with iodine *once sodium thiosulfate is used up iodine remains in solution turning starch blue black colour this is the end of the clock reaction *varying the iodide or hydrogen peroxide concentration while keeping the others constant will give different reaction times

Question 36

what method do you use to find initial rate of iodination of propanone

Answer 36

titrating(the rate of reaction for the iodine propane reaction can be followed by a continuous monitoring titrimetric method )

Question 37

# titration iodination of propanone method

Answer 37

*monitor reaction by taking samples at regular intervals *quench (stop reaction) by adding sodium hydrogen carbonate to neutralise acid *titrate samples against sodium thiosulfate and starch to work out conc of iodine *need to repeat experiment several times and change the concentration of just one reactant

Question 38

rate=k[A]ᵐ[B]ⁿ what is k

Answer 38

the rate constant the bigger it is the faster the reaction

Question 39

rate=k[A]ᵐ[B]ⁿ what are m and n

Answer 39

they are orders of reaction

Question 40

rate=k[A]ᵐ[B]ⁿ what is the overall order

Answer 40

m+n

Question 41

rate constant is always the same for certain reactions at ?

Answer 41

specific temperatures

Question 42

if you rase the temperature what happens to the rate constant

Answer 42

it will rise too

Question 43

in a series of steps which step becomes the rate determining step

Answer 43

the one with the slowest rate

Question 44

what are the rules for determining if something is in the rate determining step

Answer 44

*If reactant appears in rate equation it must affect the rate and be in rds *if reactant doesn't appear in the rate equation it isnt involved in rds

Question 45

can catalyst appear in rate equations and rate determining steps

Answer 45

yes

Question 46

does the rate determining step have to be the first step in a mechanism

Answer 46

no

Question 47

can the reaction mechanism be predicted from just the chemical equation

Answer 47

no

Question 48

# in terms of rds the order of a reaction with respect to a reactant shows?

Answer 48

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

Question 49

if a reactions second order with respect to x how many molecules of x will be in rate determining step

Answer 49

2

Question 50

Cl*(g) + O3(g) ⟶ ClO*(g) + O2(g) --slow (rate-determining step) ClO*(g) + O(g) ⟶Cl*(g) + O2(g) — fast what is the rate equation

Answer 50

rate = k[Cl*][O3].

Question 51

CH₃COCH₃(aq) + I₂(aq) + H⁺(aq) ⟶ CH₃COCH₂I(aq) + H⁺(aq) + I⁻(aq) rate = k[CH₃COCH₃][H⁺] what should you say about the reaction

Answer 51

*propanone and H+ are in the rate equation so they or something derived from them must be in the rate determining step *iodine is not in the rate equation so it is not involved until after the rate determine step *the order of reaction for both propane and H+ is 1 so the rate determine step must use 1 molecule of each *H+ is a catalyst so it must be regenerated in another step

Question 52

halogenoalkanes undergo ?

Answer 52

nucleophilic substitution

Question 53

SN1 only involve ?

Answer 53

1 molecule or ion in the rate determining step

Question 54

SN2 involve ?

Answer 54

2 molecules 1 molecule and 1 ion or 2 ions in the rate determining step

Question 55

primary halogenoalkanes only react by what mechanism

Answer 55

SN2

Question 56

secondary halogenoalkanes can react by what mechanisms

Answer 56

SN1 and SN2

Question 57

tetitary halogenoalkanes can react only by what mechanism

Answer 57

SN1

Question 58

what is the Arrhenius equation

Answer 58

k=Ae⁻ᴱᵃ/ᴿᵀ

Question 59

what do catalyst do

Answer 59

increase the rate of reaction by providing alternate reaction pathway with a lower activation energy

Question 60

what is homogenous catalyst

Answer 60

catalyst in the same state as the reactant

Question 61

what is heterogeneous catalyst

Answer 61

catalyst in different state to to the reactants

Question 62

advantages of of heterogeneous catalyst

Answer 62

*solid heterogenous catalyst provide surface for reaction to take place on catalyst may be mesh or fine powder to increase surface area *can be easily separated from from the products and leftover reactants

Question 63

disadvantages of heterogenous catalyst

Answer 63

can be poisoned which means substance clings to the surface more strongly than the reactant does preventing catalyst from getting involved in the reaction its meant to be speeding up

Question 64

*A small fixed amount of phenol is present which reacts immediately with the bromine as it is produced, thus removing it from solution. *Explain why it is essential for the amount of phenol to be small compared to the amounts of the reactants for this assumption to be valid.

Answer 64

so the phenol is used up

Question 65

A series of experiments was carried out where only the concentration of bromide ions present was varied and the solution contained a large excess of BrO3− and H+ ions. The total volume of the mixture was kept constant. Why was it important that the solution contained a large excess of BrO3− and H+ ions?

Answer 65

so that the concentration of bromide ions is the only variable

Question 66

Another ‘clock reaction’ is the ‘iodine clock’ reaction, where hydrogen peroxide solution is mixed with a solution containing sodium thiosulfate, potassium iodide and starch. H2O2(aq) + 2I−(aq) + 2H+(aq) l I2(aq) + 2H2O(l) Why are the potassium ions omitted from the above equation?

Answer 66

*becuase they are spectator ions

Question 67

what is the colour change in iodine clock reaction

Answer 67

colourless to blue black colour

Question 68

Outline a titrimetric method that could be used to measure the change in concentration of compound A with time. Compound A is an alkali, whereas compounds B, C and D are neutral. A + B ----> C + D

Answer 68

*collect samples of reaction mixture at regular time intervals *quench the mixture *Titrate with acid of known concentration/standard solution using indicator methyl orange

Question 69

Suggest an explanation, other than human error, for the two anomalous results circled on the graph. (point above line of best fit lines are the highest and further right)

Answer 69

*rate was higher than expected *reaction was exothermic so energy is released *so higher proportion of higher collisions

Question 70

how many steps is a sn2 reaction

Answer 70

one step

Question 71

in sn2 the rate of reaction depends on

Answer 71

the concentration of both reactants

Question 72

how many steps is a sn1 reaction

Answer 72

two step reaction

Question 73

in sn1 which step is the rate determining step

Answer 73

the slow step/breaking step

Question 74

S₂O₈²⁻ + 2I⁻→

Answer 74

2SO₄²⁻ + I₂

Question 75

what is evidence for a reaction having more than one step

Answer 75

*because number of particles in rate equation does not match number of particles in that equation *the number of molecules in equation for that reaction colliding simultaneously is unlikely *chance of number of reactants in the equation for the reaction colliding is unlikely

Question 76

why would reactants be in large excess in reaction

Answer 76

*so they do not affect the rate *to ensure they are virtually constant *to make sure theres only one variable constant

Question 77

what further experiment could you do to show a order of reaction with respect to a certain reactant is one and state its effect on the graph

Answer 77

*monitor the reactant over time plot concentration time graph and show that the half life is constant or *double the reactant and the rate should change by the same factor or the gradient would double too