Topic 15 Kinetics 2

Question 1

What are the units for the rate constant(K) when the overall reaction is 2

Answer 1

Mol^-1 dm^3 s^-1

Question 2

What are the units of rate constant when order of reaction is 1

Answer 2

S^-1

Question 3

What are the units of rate constant(K) when the overall order is 3

Answer 3

Mol^-2 dm^6 s^-1

Question 4

Rate of reaction definition?

Answer 4

The change in the concentration or amount of reactant used up or product produced in a given time

Question 5

What does the rate equation link?

Answer 5

The rate equation links rate with concentrations of substances.

Question 6

What is the rate constant represented by?

Answer 6

The rate constant is represented by ‘k’.

Question 7

What does a larger value of ‘k’ indicate?

Answer 7

The larger the value of ‘k’, the faster the rate of reaction.

Question 8

When is the rate constant fixed?

Answer 8

The rate constant is only fixed at a particular temperature.

Question 9

What happens to the rate constant when temperature changes?

Answer 9

If the temperature changes, so does the rate constant.

Question 10

What happens to ‘k’ when temperature increases?

Answer 10

‘k’ increases when temperature increases.

Question 11

How does increasing temperature affect particle collisions?

Answer 11

As we increase the temperature, the particles have more kinetic energy and they collide more often.

Question 12

What is the general form of the rate equation?

Answer 12

Rate = k [A]^a [B]^b

But the concentrations of the substances remain constant.

Question 13

What characterizes a zero order reaction?

Answer 13

The rate is constant and represented by a straight line graph. Changing concentration doesn’t change the rate.

Half-life decreases.

Question 14

What characterizes a first order reaction?

Answer 14

The rate changes in equal amounts and is represented by a shallow curve graph. Changing concentration changes the rate equally.

Half-life is constant.

Question 15

What characterizes a second order reaction?

Answer 15

The rate changes in unequal amounts and is represented by a steep curve graph. Changing concentration changes the rate squared.

Half-life increases.

Question 16

What are the two types of nucleophilic substitution mechanisms for halogenoalkanes?

Answer 16

The two types are SN1 and SN2 mechanisms.

Question 17

What is characteristic of SN1 reactions?

Answer 17

SN1 reactions have only 1 molecule or ion in the rate determining step.

Question 18

What type of halogenoalkanes react via an SN2 mechanism?

Answer 18

Primary halogenoalkanes react via an SN2 mechanism.

Question 19

What is characteristic of SN2 reactions?

Answer 19

SN2 reactions have 2 molecules or ions in the rate determining step.

Question 20

What type of halogenoalkanes react via SN1 and SN2 mechanisms?

Answer 20

Secondary halogenoalkanes react via SN1 and SN2 mechanisms.

Question 21

What type of halogenoalkanes react via an SN1 mechanism?

Answer 21

Tertiary halogenoalkanes react via an SN1 mechanism.

Question 22

What is a clock reaction?

Answer 22

A clock reaction is where you can time how long it takes for a reaction to occur.

Question 23

How can the initial rate of a reaction be estimated?

Answer 23

The rate of the clock reaction is a good estimate of the initial rate of the reaction.

Question 24

What is colorimetry?

Answer 24

Colorimetry can be used as a method to monitor reactions.

Question 25

How can the iodine clock reaction be monitored?

Answer 25

By sitting the reaction vessel on paper with a cross and timing how long it takes until the cross is no longer visible.

Question 26

What indicates the end point in a clock reaction?

Answer 26

The end point is indicated by a color change.

Question 27

What assumptions are made during clock experiments?

Answer 27

1. The temperature of the reaction remains constant. 2. The concentration of reactants doesn't change significantly during the time period of the reaction. 3. The reaction has not proceeded too far when the end point is seen.

Question 28

What is the relationship between the speed of the clock reaction and the initial rate of reaction?

Answer 28

The quicker the clock reaction, the faster the initial rate of reaction is.

Question 29

What is the iodine clock reaction?

Answer 29

The iodine clock reaction is a chemical reaction involving iodine and sodium thiosulfate. ## Footnote Example reaction: H2O2 + 2I- → 2H2O + I2

Question 30

What role does sodium thiosulfate play in the iodine clock reaction?

Answer 30

Sodium thiosulfate reacts immediately with the iodine produced in the reaction.

Question 31

How can the iodine clock reaction be monitored?

Answer 31

The reaction vessel can be placed on paper with a cross, and the time is measured until the cross is no longer visible.

Question 32

What indicates the end of the reaction in the iodine clock experiment?

Answer 32

When there is no more sodium thiosulfate left, the iodine reacts with starch, resulting in a deep blue/black color.

Question 33

What factors can affect the timing of the blue/black color in the iodine clock reaction?

Answer 33

Varying the concentration of iodine and/or hydrogen peroxide while keeping other conditions constant affects the timing.

Question 34

CP13 Iodine Reactions Tell the reaction

Answer 34

Equation is iodine plus propanone plus catalyst----> Iodide + catalyst + iodopropanone

Question 35

Method of Iodine reaction practical

Answer 35

Use a pipette add sample of mixture to excess sodium hydrogencarbonate immediately after removing from flask to quench reaction Withdraw samples every 3 minutes Titrate with Na2S2O3(sodium thiosulfate) adding starch indicator near the end This will turn from black to colourless Repeat for different comcentrations

Question 36

What is the iodine clock reaction equation

Answer 36

S2O8^2- +2I- ---> 2SO4^2- +I2

Question 37

Explain the iodine clock reaction

Answer 37

Add potassium persulphate to a TT containing KI,sodium thiosulfate and starch Start a stopwatch Stop clock when solution goes blue black

Question 38

When is Investigating the ROR by measuring the change in volume of gas applicable

Answer 38

This works if there is a change in the number of moles of gas in the reaction. Using a gas syringe is a common way of following this. (CH3)2C=CH2(g) + HI(g) (CH3)3CI(g)

Question 39

When is it applicable to investigate the ROR using a change in mass measurement

Answer 39

This works if there is a gas produced which is allowed to escape. Works better with heavy gases such as CO2 HCOOH(aq) + Br2(aq)  2H+(aq)+ 2Br - (aq) + CO2(g)

Question 40

When is it applicable to investigate the ROR using calorimetry

Answer 40

If one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixtures

Question 41

When is it applicable to investigate ROR using electrical conductivity

Answer 41

Can be used if there is a change in the number of ions in the reaction mixture

Question 42

How to find out if a rate conc graphs is 1st order

Answer 42

If the half lives are constant

Question 43

How to find out if conc time graph is 2nd order

Answer 43

If half life rapidly increases