Topic 16: Kinetic II

Question 1

What are some of the possible methods of measuring the rate of reaction?

Answer 1

Measuring vol of gas produced
Measuring change in mass of a reaction mixture
Monitoring a colour change (colourimetry)
Measuring the change in conc of reactant/product using titration
Measuring change in pH of a solution
Measuring the change in electrical conductivity of a reaction mixture

Question 2

Give the rate equation for a first order reaction

Answer 2

rate = k[A]

Question 3

Give the rate equation of a second order reaction

Answer 3

rate = k[A]^2

Question 4

Give the rate equation of a 0 order reaction

Answer 4

rate = k

Question 5

What is the rate determining step

Answer 5

The slowest step in the mechanism for a reaction which determines the spreads at which the overall reaction proceeds

Question 6

How can you deduce the slowest step from the rate equation

Answer 6

The rate equation only contains species involved in the rate determining step

Question 7

If something appears in the rate equation but is not in the reaction mechanism, it must be a…

Answer 7

Catalyst

Question 8

What shape of a conc-time graph indicates a 0 order reaction ?

Answer 8

Negative gradient
RoR does not change

Question 9

What shape of a conc-time graph indicates a 1st order reaction ?

Answer 9

Downward curve
RoR slows

Question 10

What shape of a conc-time graph indicates a 2nd order reaction ?

Answer 10

Steeper downward curve

Question 11

How do you calculate k for a 0 order reaction using the conc-time graph

Answer 11

Calculate the gradient of the line

Question 12

How do you calculate k for a 1st order reaction using a conc-time graph

Answer 12

Draw a tangent at a given concentration
Calculate the gradient of that line to get the rate
Substitute the 2 values into the rate equation to find k

Question 13

How can half life be used to determine the order of a reaction from conc-time graphs

Answer 13

1st order reactions - half life is constant
2nd order reactions - half life increases

Question 14

Describe the shape of a rate-conc graph for a 0 order reaction
How would you find k from this graph ?

Answer 14

Flat line
Y-intercept gives the value of K

Question 15

Describe the shape of a rate-conc graph for a 1st order reaction
How would you find k from the graph ?

Answer 15

Positive correlation line (upwards diagonal)
Gradient of line gives us k

Question 16

Describe the shape of a rate-conc graph for a 2nd order reaction
How would you find k from this graph ?

Answer 16

Upwards curve
To calc k you would need to plot a second graph (rate vs conc^2) and then the gradient would be k

Question 17

What does the Arrhenius equation show us

Answer 17

How the rate constant (k) and temperature (T) are related exponentially

Question 18

Explain how the Arrhenius equation is used graphically

Answer 18

.Ea. 1.
ln K = —- —- + lnA
.RT. T
y =. m. x + c

lnA = y intercept
Ea= activation energy
T = temp in kelvin
R= gas constant

Question 19

What are the two types of mechanisms for nucleophilic substitution reactions

Answer 19

SN1 and SN2

Question 20

What does an SN1 reaction entail

Answer 20

Only 1 molecule involved in the rate determining step
Used in the hydrolysis of tertiary halogenoalkanes
2 step reaction
Intermediate formed

Question 21

What does an SN2 reaction entail

Answer 21

2 molecules involved in the rate determining step
Used in the hydrolysis primary halogenoalkanes
End up with a transition state