kinetics

Question 1

What is meant by homogenous and hetergenous reactions

Answer 1

homo- reactions occur in one phase

Heter- occur in different phases

Question 2

what are the units for 1st order reaction

Answer 2

S^-1

Question 3

what are the units for second order reactions

Answer 3

cm³ mol^-1 s^-1

Question 4

What are elementary reactions

Answer 4

molecules of LHS come together in a single encounter to form molecules on RHS.

Question 5

what is the intergrated rate law of first order reaction and how would you plot

Answer 5

C_o = C_o e^-kt

^{plot ln(C) and time}

Question 6

What is the intergrated rate law for second order reactions and what would you plot on a graph

Answer 6

be careful of stiochiometry

Question 7

What is M in pseudo second order reactions and why is it important

Answer 7

M is an inert collision factor and takes away XS energy, without the product form will be unstable and will dissociates.

Question 8

how do recombination reactions occur

Answer 8

either one single step (highliy unlikely that 3 molecules will collide) or a series of biomolecular steps ( this is more effcient and faster)

all depends on if A₂^* lives long enough to experience a stablilising collision with M. If made of many atoms there are more vibrations where xs energy can hide

Question 9

What is the integrated rate law for zero order reactions and what do you plot

Answer 9

C(a)t = C_a^o - kt

plot conc and t/s

Question 10

describe the stirring reactor and any disadvantages it has

Answer 10

Is a flow method and involves stirring the reactants and the product is then taken for quench analysis. Typically used for reactions between 10ms<t></t>

<p>faster reactions can not be studied in this way </p>

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Question 11

describe the flow tube method

Answer 11

Reactants are introduced into the tube and the reactants are mixed and the reaction begins. Product concentration is measured at distance L

t= V/L

suitable for reactions which are t>10ms

Question 12

What is a disadvantage of the flow tube method and how is this overcome

Answer 12

A large volume of the sample is consumed

to overcome this a stopped flow technique is adopted. The reactants are mixed which drives a plate. when the plate hits and end the flow is stopped and no more sample is consumed. the products are analysed using spectroscopic techniques.

Question 13

What are relaxation methods

Answer 13

techniques where an equilibrium is disturbed and the return to equlibrium is measured.

Question 14

describe the shock wave tube method

Answer 14

reaction is contained in a compound at thermal equilibrium and is contained in a high pressure compartment. It is seperated from a low pressure compartment by an aluminium membrane. The membrane burst and the mixyure travels as a shock wave. The products are measured via light absorbtion.

Question 15

descirbe the flash photolysis method

Answer 15

in a homogenous reactions a flash of light creates a reactive species which starts to react. The reaction is monitored by spectroscopy.

Question 16

What is the fundamental limit of flash photolysis

Answer 16

time resolution which is detrmined by the duration of the flash. Ultra shorts lasers are used which produce best time resolution. The flash also needs to be small

Question 17

What is the Arrhenius eqaution after log has been applied to both sides.

Answer 17

Ln k (t) = Ln A + E_a/RT

Question 18

What are the parameters of the Arrhenius equation

Answer 18

A = pre expontential factor 
E<sub>a</sub> = Activation energy

Question 19

How would you graphically represent the arrhenius equation

Answer 19

Plot Ln k on the y axis and 1/T on the x axis.

This would mean Ln A is the intercept - e^c and the gradient will be E_{a =} mR where m is gradient and R is the gas consrant