12. Kinetics

Question 1

Thermodynamics vs kinetics: what do they tell us?

Answer 1

Question 2

Kinetic stability vs thermodynamic stability

Answer 2

ex.: H₂O₂ decomposition to produce O₂ (elephant toothpaste)

Question 3

Explain what is kinetics and what it deals with

Answer 3

Question 4

What are the possible progressions / mechanisms of reactions

Answer 4

• One step
• Two step
• Unimolecular (one molecule involved)
• Bimolecular (two molecules involved)

In the overall reaction 3 molecules involved ut needs to be split up into steps to determine molecularity

Question 5

What are the potential energy contour plots, explain them

Answer 5

Question 6

How are the rates of rreactions measured experimentally?

Answer 6

Question 7

What is the definition of rate of a reaction?

Answer 7

Rate - the slope at a particular time / concentration

Question 8

How to calculate the rate of a recation from a data plot?

Answer 8

Rate - the slope at a particular time / concentration

Question 9

How can the reaction rates of different secies in the same reaction be determined from a reaction equation?

Answer 9

According to the reaction equation ratios - relative differences in rates of different species in the same reaction

Question 10

What is the Rate Law? Explain the concept

Answer 10

• Rate Law can only be dteermined experimentally
• The Rate Law: expresses the rate of reaction in terms of the molar concentrations of the species in the overall reaction
• Rate constant k: independent of the concentration of species in the reaction but depends on temperature

Question 11

What does the reaction order explain about the reaction?

Answer 11

Question 12

How is the rate of a reaction determined and how can it be expressed?

Answer 12

Question 13

What is the zeroth order plots for conc vs time and rate vs conc

Answer 13

Question 14

What is the first order plots for conc vs time and rate vs conc

Answer 14

As conc decreases, so does the rate

Question 15

What is the second order plots for conc vs time and rate vs conc

Answer 15

As the conc drops, the rate drops even quicker

Question 16

What is the integrated rate law for a zeroth order reaction?

Answer 16

Question 17

What is the integarted rate law for first order reaction?

Answer 17

Question 18

What is the integarted rate law for second order reaction?

Answer 18

Question 19

What is the difference between the first order differential rate law and integrated rate law?

Answer 19

Differential rate law gives rate in terms of conc

Integrated rate law gives rate as a function of time

Question 20

What is the order of radioactive decay and why

Answer 20

1st order because the rate of decay will be dependent only on the number of species that are in the block + each nucleus of the species has an equal chance of decay → number of decays per unit time depends on the number of nuclei

Question 21

How does carbon dating works? How to estimate length of time since death?

Answer 21

Question 22

What is the differential rate law for first order A+B→products? Why

Answer 22

Because the collision frequency only depends how often A and B collide and react, so the higher the conc - the more collisions

Question 23

How does the integrated rate law look for first order A+B→products reaction?

Answer 23

Complex but can be simplified when said that on of reactants is in large excess

Question 24

How do differential rate laws combine in equilibrium?

Answer 24

Question 25

How can thermodynamics and kinetics be related at equilibrium?

Answer 25

Question 26

What are the two ways to determine rate law from experimental data?

Answer 26

Rate laws can only be datermined experimentally → calculated in two ways

Question 27

How is the initial rate law determined from experimental data?

Answer 27

Measuring the tangent at the very start of the curve - linear relationship for some time

Question 28

Explain how to determine reactions order via initial rate method

Answer 28

x

Question 29

Explain how to determine reactions order via method of integration

Question 30

Key points from rate law

Answer 30

Question 31

When does rate constant k change?

Answer 31

When temperature changes (when increases - increase in k - rate increases) rate decreases when T raised above certain point - catalysed by enzymes (denature)

Question 32

Which equation describes the relationship between k and T?

Answer 32

Arrhenius equation (molecules have to have a threshold of E to be able to react)

Question 33

What is a reaction profile?

Answer 33

Question 34

How to determine Ea and A for a particular reaction?

Answer 34

A - measure of frequencies of collisions in the correct orientation to react

Question 35

Explain catalysts (define, working mechanism, types)

Answer 35

both forward and reverse reactions are catalysed at the same time

Question 36

What is the detailed mechanism of metal catalysts?

Answer 36

* catalyst provides lower energy pathway * reactants form weak bonds with the metal → after some time start making bonds with the surface → make bonds between each other * Example: liquid oil to margerine using Ni catalyst

Question 37

How do catalyst alter the activation energy curve?

Answer 37

* very high E needed to split gaseous H₂ - with Ni not needed * free E change same with or without of catalysts

Question 38

Catalysis of ammonia synthesis

Answer 38

* breaking NH₃ bonds - very much E - could only occur in very high T - with Fe catalysts low E pathway for breaking the bonds (but still E needed)

Question 39

Summary of all equations in kinetics

Answer 39