Kinetics (all topics)

Question 1

Is the rate constant temperature dependent?

Answer 1

Yes, but independent of concentrations

Question 2

What are some of the physical methods of monitoring reaction dynamics apart from monitoring concentration?

Answer 2

Monitor absorbance, conductance, laser excitation, pressure

Question 3

According to Arrhenius what does a high Ea indicate?

Answer 3

A strong T dependance of the rate

Question 4

What is the value of the gas constant, R?

Answer 4

8.314 JK-1mol-1

Question 5

What information can we get form the graphical plot of the Arrhenius expression? What are the axes labels?

Answer 5

gradient = Ea/RT
y-intercept is lnA
link against 1/T

Question 6

What is a fundamental principle of collision theory?

Answer 6

rate= collision frequency x fraction of collisions with sufficient energy

Question 7

What new quantity does transition state theory define?

Answer 7

Free energy of activation

Question 8

What is the method of integration for rate laws?

Answer 8

Graphical:
1st order: ln[A] vs t
2nd order: 1/[A] vs t

Question 9

What assumption does pseudo order reaction theory make?

Answer 9

That the concentration of one of the reactants does not change considerably

Question 10

Would the half life method graphically give a straight line or curve for 1st and 2nd order reactions?

Answer 10

1st: linear
2nd: curve

Question 11

What theory does the isolation method for derivation of rate law make use of?

Answer 11

Pseudo order reaction theory

Question 12

Describe the initial rate method for deriving rate constants and orders?

Answer 12

Vary [A] keep [B] and [C] constant. Ratios of rates can get experimental orders and then finally rate constant, k.

Question 13

What are the units of the rate constant, k for 1st, 2nd and 3rd order reactions?

Answer 13

0 order: moldm^-3s^-1
1st: s^-1
2nd: mol^-1dm^3s^-1
3rd: mol^-2dm^6s^-1
(Can be derived by putting individual units in to rate law)

Question 14

What are the 4 types of reactions we are concerned about for deriving rate data?

Answer 14

Reversible, pre-equilibrium followed by reaction, concurrent, consecutive

Question 15

How can k1 and k-1 be calculated individually?

Answer 15

Temperature-jump relaxation method

Question 16

For a concurrent reaction, what does the ratio of individual rate constants tell us?

Answer 16

Ratio of formation of individual products

Question 17

What method can we use for reversible reactions to derive rate constants?

Answer 17

Distance from equilibrium graphical method. Method of integration can’t be used

Question 18

What is the steady state approximation?

Answer 18

For k2»k1. Concentration of intermediate is found to achieve a constant value. dB/dt = 0

Question 19

What are the steps in a radical chain reaction?

Answer 19

Initiation, propagation, retardation, branching, termination, inhibition.

Question 20

What is the Lindemann mechanism?

Answer 20

Unimolecular collisions provide energy for the reaction. Activated molecules then react in a first order reaction

Question 21

What are the two types of polymerisation?

Answer 21

stepwise and radical

Question 22

According to Langmuir-Hinshelwood Kinetics what is the rate determining step in heterogenous catalysis reactions?

Answer 22

Surface reaction is RDS

Question 23

What does Vmax represent in Michaelis-Menton kinetics?

Answer 23

Saturation of the enzyme