Kinetics

Question 1

RATE LAW

Answer 1

rate law is the expression in which rate of a reaction is given by molar conc of reactants with each term raised to some power which may or may not be equal to the stoichiometric coefficient of reacting species in a balanced chemical equation

Question 2

rate equation for:

2NO(g) + O2(g) —-> 2NO2(g)

Answer 2

Rate = k [NO]^2 [O2]

Question 3

rate equatn

CHCl3 + Cl2 —> CCl4 + HCl

Answer 3

Rate = k[CHCl3] [Cl2]^1/2

Question 4

rate equatn

CH3COOC2H5 + H2O —> CH3COOH + C2H5OH

Answer 4

Rate = k [CH3COOC2H5] [H20]^0

Question 5

Factors affecting rate of reaction

Answer 5

1. conc of reactants
2. temperature
3. catalyst
4. surface area
5. exposure to radiation
6. nature of reactants

Question 6

when conc of reactants is expressed in gases in term of partial pressure then unit of rate of reaction

Answer 6

atm / s

Question 7

READ QUESTION CAREFULLY

In a reaction, 2A —-> Products, the concentration of A decreases from 0.5 mol L-1 to 0.4 molL-1 in 10 minutes. Calculate the rate during this interval?

average rate

Answer 7

1. Rate = -1/2 Δ[R]/Δt
2. Δ[R] = 0.4 -0.5
   =- 0.1
3. rate = 1/2 x 0.1 /10
   = 5 x 10^-3 mol L-1 s-1

divide carefully

Question 7

.For the reaction R—>P, the concentration of reactant changes from 0.03 M to 0.02 M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.

average rate

Answer 7

1. Δ[R] = 0.02 - 0.03
   = - 0.01
   Δt = 25 min
   ∴ rate = - Δ[R]/Δt
   =0.01/ 25
   = 4 x 10^-4 mol L^-1 min^-1
2. in sec
   rate = - Δ[R]/Δt
   =0.01/ 25 X60 = 6.66 x 10^-6 mol L^-1 s-1

Question 8

order of reaction

Answer 8

sum of power of conc of reactants in the rate law expression
1. can be for elementary and complex reanx
2. experimental reacn
3. zero or even an integer
4. for complex rnx; order given by slowest step

Question 9

ELEMENTARY REACTION

COMPLEX REACTION

Answer 9

1. single step reaction
2. sequence of elementary reaction (called mechanism) gives us the product

Question 10

UNIT of rate constant

rate constant = k

Answer 10

Mol^n-1 L^1-n s-1

let order be n

1. 0 order = mol L-1 s-1
2. 1st order = s-1
3. . 2nd order = mol-1 L s-1

Question 11

MOLECULARITY

Answer 11

THE no. of reacting species taking part in an elementary reaction that must collide simultanously to bring about a chemical rnx

1. only for elementary rnxs
2. can’t be integer or 0
3. theoretical value
4. molecularity for slowest step is same as the ORDER of overall rnx

please consider REACTANTS STOICHIOMETIC NO. AND ADD THEM

Question 12

Find Molecularity

1. NH4NO2 —> N2 +H20
2. 2 HI —>H2 +I2
3. 2NO + O2 —-> 2NO2

consider ONLY reactants

Answer 12

1. UNIMOLECULAR
2. BI
3. TRI

Question 13

The conversion of molecules X to Y follows second order kinetics. If concentration of X is increased to three times how will it affect the rate of formation of Y ?

Answer 13

1. the reaction is : X—>Y
2. According to rate law,
   rate = k[X]2
3. If [X] is increased to 3 times, then the new rate is
   rate’ = k[3X]2
   rate’ = 9 k [X]2 = 9 rate
   Thus, rate of reaction becomes 9 times and hence rate of formation of Y increases 9-

Question 14

Pseudo first-order reaction

Answer 14

a second-order or bimolecular reaction that is made to behave like a first-order reaction.
This reaction occurs when one reacting material is present in great excess or is maintained at a constant concentration compared with the other substance

Question 15

Example of psuedo first order rnx

Answer 15

1. hydolysis of ethyl acetate
   CH3COOC2H5 + H2O = CH3COOH + C2H5OH
   R = K[CH3COOC2H5] [H2O]^0
2. inversion of cane sugar
   C12H22012 + H20 = C6H12O6 + C6H12O6
   R = K[C12H22O12] [H2O]^0

Question 16

INTEGRATED RATE EQN OF ZERO ORDER

Answer 16

K= [R] - [R]0/ t

Question 17

EXAMPLES OF ZERO ORDER

ITHOTINHIERE

Answer 17

1. SOME enzyme catalysed reaction and reactions which occur on metal surface
2. decomposition of GASEOUS AMMONIA ON HOT PLATINUM SURFACE AT HIGH TEMP
   2NH3__1130K platinum_________> N2 + 3H2

rate = k[NH3]^0
= K
MOLECULARITY = 2

3. THERmal decomposition of HI ON GOLD SURFACE

Question 18

INTEGRATED RATE EQN OF FIRST ORDER

Answer 18

1. ln [R] = -kt +ln [R]0
   y = mx + c
2. k = 2.303/t log [R]o/[R]
   for graph: log[R]o/[R] = kt/2.303
   y = mx + c

Question 19

examples of FIRST ORDER RNX

Answer 19

1. hydrogention of ETHENE
   C2H4 + H2 = C2H6
   RATE = K [C2H4]
2. ALL NATURAL AND RADIOACTIVE DECAY OF UNSTABLE NUCLEI
   RATE = K [RA]
3. decomposition of N2O5 AND N2O`

Question 20

HALF LIFE OF 0 ORDER

Answer 20

t1/2 = [R]0/ k
* t1/2 directly proportional to initial conc and inversely prop to k

Question 21

HALF LIFE OF 1ST ORDER

lo2 = 0.301

Answer 21

t1/2 = 0.693/k
* t1/2 is independent of initial conc

Question 22

Arrhenius EQUATION

TEMP DEPENDENCE OF THE RATE OF RNX

Answer 22

K= A e ^ -Ea/RT

k = rate constant
A =* pre-exponential factor **OR arhennius factor or frequency factor
E_{a} = activation energy (in the same units as RT) (joules / mole)
R = universal gas constant (8.314)
T = absolute temperature (in Kelvin)

Question 23

WHat happens to rate when the temperature increases to 10degree

Answer 23

RATE IS DOUBLED

Question 24

ACTIVATION ENERGY

Answer 24

THE energy required to form intermediate called activated complex *** joules/ mol**

Question 25

plot graph from **ln k = - Ea/RT +ln A**

Answer 25

**ln k = - Ea/RT +ln A** y = lnk x = 1/T m= -Ea/R c= ln A

Question 26

Activation Energy when 2 temperature and 2 rate constant is given

Answer 26

**log k2/k2= -Ea/2.303 R [T2-T1/T1T2]**

Question 27

EFFECT OF CATALYST

Answer 27

* REDUCING** Ea** BTWN REACTANTS AND PRODUCTS and hence lower the **potential energy barrier**

Question 28

INHIBITOR

Answer 28

the substance when added reduce the rate of rnx

Question 29

hOW does catalyst affect GIBBS ENERGY ## Footnote SIKE

Answer 29

it DOES NOT alter gibbs energy * it catalyses spontaneous rnx and not non spontaneous rnx

Question 30

hOW does catalyst affect EQUILIBRIUM CONSTANT ## Footnote SIKE AGAIN

Answer 30

it DOES NOT change Kc but helps in attaining equilibrium faster * it catalyse forward and backward rnx to the same extend * so equi state remain constant but reached FASTER

Question 31

COLLISON FREQUENCY (Z) | dontforgetV

Answer 31

the no. of collision per sec **per unit volume** of rnx mixture

Question 32

effective collision why proper orientation needed?

Answer 32

1. molecules should collide with sufficient kinetic energy (threshold energy) 2. proper orientation to faciliate breaking of bonds between reating species and formation of new bonds to form products ## Footnote e.g. for proper ori is bromomethane

Question 33

consider steric factor p and collision frequency z then RATE will be?

Answer 33

Rate = *P*Zab e-Ea/RT

Question 34

drawback of COLLISION theory

Answer 34

1. consider atoms and molecules as hard sphere 2. ignores their structural aspect