Kinetics

Question 1

What are the stoichiometric coefficients

Answer 1

Reactants = -ve no. moles

Products = +ve no. moles

Question 2

What is the rate of reaction equation

Answer 2

Vc = 1/Vi + dni/dt

Question 3

What is the equation for the rate constant

Answer 3

Vc = k c1^m1 c2^m2 c3^m3 …

Question 4

What is the molecularity

Answer 4

How many molecules
are involved as reactants
in an elementary reaction step

Question 5

What is a unimolecular reaction

Answer 5

One molecule reacts
in essential reaction step

Question 6

What is a bimolecular reaction

Answer 6

Two molecules react
in essential reaction step

Question 7

What is a trimolecular reaction

Answer 7

Three molecules react
in essential reaction step

Question 8

What is the integrated rate law for a first order reaction

Answer 8

c(t) = co exp(-kt)

Question 9

What is the half life of a first order reaction

Answer 9

Time when c(t) = 1/2 co
t1/2 = ln2/k

Question 10

What is the mean lifetime of a unimolecular reaction

Answer 10

Time when c(t) = 1/e co
𝜏 = 1/k

Question 11

What is the integrated rate law of a bimolecular reaction if cAo = cBo

Answer 11

1/c(t) = 1/co + kt

Question 12

What is the integrated rate law of a bimolecular reaction if cAo ≠ cBo

Answer 12

ln(cB(t)/cA(t)) = ln(cBo/cAo) + (cBo - cAo)kt

Question 13

When is a bimolecular reaction pseudo-first order

Answer 13

If A in great excess
[A] doesn’t noticeably change

Question 14

When is a trimolecular reaction pseudo-second order

Answer 14

M is an inert collision partner
often [M] doesn’t change noticeably

Question 15

What are the options for a recombination reaction

Answer 15

1 trimolecular step

Sequence bimolecular steps

Question 16

When is bimolecular recombination possible

Answer 16

If A* lives long enough
to experience stabilising collision w/ M

Question 17

Examples of recombination reactions

Answer 17

Bi preferred: polyatomic & radicals

Tri preferred: atoms
A* molecule too short lived

Question 18

What is the equation for reversible reactions

Answer 18

Vc(t) = -d[A]/dt = ka[A] - kb[B]

Question 19

What is the integrated rate law for unimolecular reversible reaction

Answer 19

ΔcA(t) = ΔcAo exp(-(ka + kb)t)

Question 20

What is the relaxation time of a reversible unimolecular reaction

Answer 20

Time where ΔcA = 1/e ΔcAo
𝜏R = 1/ (ka + kb)

Question 21

How is the thermodynamic equilibrium constant worked out

Answer 21

Equilibrium => Vc = 0

K = ka/kb = [B]eq/[A]eq

Question 22

What is a zeroth order reaction

Answer 22

Rate of reaction is constant

Vc = k

Question 23

What is the Beer-Lambert law from spectroscopic detection

Answer 23

I = Io exp(-σcl)

∴ A = σcl

Question 24

What are the flow methods

Answer 24

Stirring reactor

Flow tube

Stopped flow

Question 25

What is the disadvantage of stirring reactor

Answer 25

Thorough mixing => time
not suitable for studying fast reactions

Question 26

How does a flow tube work

Answer 26

Mixture flows with velocity through the tube
reactants mix in tube

Question 27

What is the equation for a flow tube

Answer 27

l = v t

Question 28

How does stopped flow work

Answer 28

Two syringes drive reactants into mixing chamber

Mixture passes spectrometer

Stops at stopping syringe

Question 29

What are the relaxation methods

Answer 29

Shock wave tube

Flash photolysis

Question 30

What is a relaxation method

Answer 30

Mixture is in equilibrium
sudden perturbation creates deviation
return to equilibrium monitored

Question 31

How does a shock wave tube work

Answer 31

Mixture contained at room temp in high pressure
separated by membrane (eg. Al foil)
from low pressure compartment

Membrane bursts
mixture travels at shock wave
into low pressure compartment

New equilibrium establishes
concentration measure by light absorption
as wave passes through light beam path

Question 32

How does flash photolysis work

Answer 32

Homogeneous mixture
Light flash causes reaction to start
Reaction monitored by spectroscopy

Question 33

What does two consecutive t1/2 values show

Answer 33

Reaction is first order

Question 34

How can >2 sets of initial rates be used to calculate the reaction order

Answer 34

Plot ln(Vco)/ln[Ao]
reaction order = gradient of slope

Question 35

What is the Arrhenius equation

Answer 35

ln(k) = ln(A) - Ea/RT

Question 36

What are the units of A from the Arrhenius equation

Answer 36

Same units as rate constant

Question 37

What is the role of M in a reaction

Answer 37

Inert collision partener

Question 38

What is the pre-equilibrium

Answer 38

Activation & deactivation steps
in thermodynamic equilibrium
not disturbed by the reaction step

Question 39

What is the effect of a fast pre-equilibrium on the rate constant equation

Answer 39

k(x)[A*] = k(x)k[A]

Question 40

How can you work out the temperature dependance of keff

Answer 40

keff = k(x) exp(-ΔE/RT)

Question 41

What is the steady state approximation

Answer 41

d[X]/dt ≈ 0

Question 42

What are the stages of a chain reaction called

Answer 42

Initiation

Chain propagation
Inhibition/retardation
Branching

Termination

Question 43

What is the role of I⋅

Answer 43

Chain carrier

Question 44

What is a linear chain reaction

Answer 44

Chain reaction w/out branching

No. chain carriers doesn’t increase

Question 45

What is a branched chain reaction

Answer 45

Chain reaction w/ branching

No. chain carriers increases

Question 46

When is the Rice-Herzfeld consistent with stoichiometry

Answer 46

When k1 is negligible

Question 47

How can the rate constant of a bimolecular reaction be estimated

Answer 47

k = σ vrel

Question 48

What is the bimolecular rate constant with regards to temperature

Answer 48

k(T) = (8(kb)T/πμ)^1/2