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Chemical Kinetics is the branch of chemistry which deals with the rate of change of conecentration from
intial state to final state under non-equilibrium conditions and the factors affecting the rate of reaction.
RATE OF REACTION
The rate of reaction is defined as the change in conecentration of reactants or products in unit time.
Rate of reaction
=
taken
Timeion of reactants/ Products concentrat
in Change
Rate can be defined in two ways :
(i) Average Rate:-
The rate of reaction measured over a time interval is defined as the average rate of reaction.R
av.=
Ct tC Ct1 2
1 2
(ii) Instanteneous Rate :-
The rate of reaction at any given instant is defined as the instanteneous rate .“
It is simply the slope of concentration time graph at that particular instant”r =av – [R] –[C – C ]2 1 rinst= d[P] [t – t ]2 1 t [R]0 [P] C1 C2 t2 time time co n ce n tr at io n co n ce n tr at io n t1 slope = dt =
(a)
(b)
Dependence of rate on Stoichiometry
For any Reaction n1A +n2 B n3C + n4D
dtD d n dtC d n dtB d n dtA d n1 [ ] 1 [ ] 1 [ ] 1 [ ] Reaction of Rate 4 3 2 1
For reactants negative sign is used because the concentration of reactantsdecreases with time.
For products positive sign is used because the concentration of products increases with time.
Specific care should be taken while dealing with this expression here ,By
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dtA d n11 [ ]
=
rate of reaction where asdtA d ][
=
rate of disappearence of A dtC d n11 [ ]
=
rate of reaction where asdtC d ][
=
rate of appearence of CExample 1. For the reaction:
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
The concentration of NO changes from 1.8M to 5.4 M in 100 seconds than calculate
-(i) Rate of disappearence of Ammonia (ii) Rate of reaction
Solution - Rate of appearence of NO
=
3.6 102molL-1sec11001.8) 4 . 5 ( ] [ dtNO d Now from the rate expression
dtO H d dtNO d dtO d dt NH d [ ] 61 ] [ 4 1 ] [ 51 ] [ 4 1 Reaction of Rate 3 2 2
Rate of disappearence of NH
3=
1 1 -2 3 [ ] [ ] 3.6 10 molL sec 4 4 ] [ dtNO d dtNO d dt NH d(ii) Rate of reaction = 3.6 10 2 9 10 3 molL-1 sec 1
4 1 ] [ 4 1 dtNO d
LAW OF MASS ACTION
According to this law the rate of a chemical reaction is directly
proportional to the product of active masses of reactants raised to the power their stochiometric coefficients.
For any reaction n1A + n2B n3C + n4D
2 1 2 1 ] [ ] [ ] [ ] [ n n n n
B
A
K
Rate
B
A
Rate
This expression is called rate expression or rate law. Active Mass - For aqeous phase active mass can be replaced by concentration (Molarity).
For gaseous reactants active mass can be replaced by either concentration or partial pressure.
Here ‘K’ is called the rate constant or specific rate of the reaction.Greater is the value of rate constant more will be the rate of reaction.
Note :-1. The reagent which is present in excess is not included in the rate law, since the change in its concentration is insignificant.
2. Intermediates are not involved in the rate law they has to be eleminated if are present in the rate law.
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ORDER AND MOLECULARITY
MOLECULARITY :-The number of reactant molecules which collide with each other in a chemical reaction to form products is called the molecularity of the reaction.On the basis of Molecularity reactions can be classified as
Br2 2Br - Unimolecular H2 + I2 2HI - Bimolecular 2NO + O2 2NO2- trimolecular
Note :- 1. Molecularity can niether be zero , negative , fractional and infinite.
2. Moleuclarity is a theoretical quantity.
3. Molecularity of a reaction cannot be greater than 3 because more than 3 molecules can’t collide effectively to form products. 4. Molecularity is independent of pressure and temperature. 5. Molecularity of a single step reaction i.e. simple reaction is the number of molecules participating in the reaction.
6.But for a complex multistep reaction the molecularity of each step is different and there is no meaning of overall molecularity of the reaction
ORDER It is defined as
-“The sum of the powers of all the concentration terms included in the rate law” n1A + n2 B products 2 1[ ] ] [A n B n k rate Order of reaction = (n1+n2)
Note:- 1. Order of a reaction is an experimentally determined quantity. 2. Order can be zero, negative and fractional but cannot be infinity.
3. Order depends on pressure and temperature.
4. For a multistep complex reaction the overall order of the reaction is determined by RDS(Rate Determinind Step).
Example 2 : For the reaction 2H2 + 2NO N2 + 2H2O, the following mechanism has been suggested:
(i) 2NO N2O2 equilibrium constant K1 (fast) (ii) N2O2 + H2 k2 N
2O+ H2O (slow) (iii) N2O + H2 k3 N
2 + H2O (fast) Determine the order of the reaction
Sol:- The slowest step is the rate RDS(Rate Determining Step) N2O2 + H2 k2 N
2O+ H2O (slow)
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But since N2O2 is an inetermediate it cannot be included in rate law so it has to be elemintaed
So for the equilibrium reaction 2NO N2O2 equilibrium constant K1
2 1 2 2 2 2 2 1 [ ] [ ] [ ] ] [ N O K NO NOO N K replacing [N2O2] in equation ..(1) Rate = KK1[NO]2[H 2] = K’ [NO]2[H2] So the order of the reaction = 2+1 = 3
The molecularity of each step is as follows: (i) 2 (ii) 2 (iii) 2
Significance of the Order Of Reaction
The order of a reaction is different with repect to each reactant. The order with respect to a particular reactant tells that how the rate of reaction will change on changing the concentration of that reactant. For example consider the rate law
rate = k [A]2[B]3
So if concentration of A is doubled than rate of reaction will become four times as the order with respect to A is 2.
if concentration of B is doubled than rate of reaction will become 8 times as the order with respect to B is 3.
Types of reactions on the basis of order
ZERO ORDER REACTIONS Consider a general reaction
A Products at t=0 [A0]
at t=t [At]
Since the order iszero so the rate of reaction can be written as Rate = d[Adtt]=k[A
t]0 ] d[At =kdt On integrating [At] = -kt + c At t=0, [At] = [A0] , So c = [A0]
So for zero order reaction [A]t = [A]0 – kt Half Life
“the time taken for the concentration of reactants to decrease to half of its initial value”
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[A] conc. time Rate time Examples :(i) Photochemical Reactions
H2(g) + Cl2 (g) h 2HCl (g)
(ii) Decomposition of substances over metal surface
N2O(g) hotSurfacePt. N2 (g) + 2 1
O2 (g) 2NH3 (g) MosurfaceorW N2 + 3H2
(iii) Enzyme catalysed reaction
Substrate(S) Enzyme(E) product(P). FIRST ORDER REACTION Consider a general reaction
A Products at t=0 [A0] = a
at t=t [At]= (a-x)
Since the reaction is of first order the rate of reaction can be written as
Rate = d[Adtt]=k[A
t]1 On integrating we get , 1 ln [[ 0]] t A A t k ] [ ] [ log 303 . 2 0 10 t A A t k or ) ( log 303 . 2 10 aa x t k
The Exponential form of 1st order equation is [A]
t = [A]0ekt Half -life : t1/2 = k
693 . 0
For a first order reaction half life is independent of initial concentration of reactant.
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t1/2 aThe equation
1 ln [[ 0]] t A A t k , can be written asln[Ao] - ln[At] = kt or ln[At] = -kt + ln[Ao]
The graph between ln[At] and t will be a straight line with negative slope, and
slope = rate constant (k)
In [A]t
t
log [A]10 t
t
If the graph is plotted between ln[At] and t the slope will be equal to k and if the graph is plotted between log10[At] and ‘t’ the slope will be 2.303k .
Examples:
(i) Radioactive disintegration is a first order reaction.
(ii) C12H22O11 + H2O
H
catalysed
Inversion
hydrolysis
C6H12O6 + C6H12O6. (glucose) (fructose) (iii) Mineral acid catalyzed hydrolysis of esters.(iv) Decomposition of H2O2 in aqueous solution.
Methods To Calculate the rate constant of First Order Reaction
1. By Titration:- In this method an unknown solution (say ‘A’) is titrated against a standard solution of known concentration(Say ‘B’). The volume of standard solution required at different time intervals is measured from which the concentration of unknown solution can be calculate .
Vo = Volume of standard solution used at time t = 0 Vt = Volume of standard solution used at time t
V = Volume of standard solution used at completion of titration i.e.
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So, V- Vo Initial amount of A present
V - Vt Amount of A present at any time t
] [ ] [ ln 1 0 t A A t k k = t o V V V V t log 303 . 2
2. By Measuring angle of
rotation:-In this method the total angle of rotation of the sample is measured at different time intervals from which we can calculate the amount present at any given time. Consider a reaction:
A B If
r0 = initial angle of rotation of the sample (when only A is present) rt = angle of rotation after time t (when both A and B are present)
r = angle of rotation after completion of reaction (when only B is present)
r0- r Initial amount of A present
r - rt Amount of A present at any time t
k = r r r r t log t0 303 . 2 3. By Measuring Pressure A(g) B (g) + C(g) at t=0 Po at t=t Po- x x x
Total pressure at time t Pt = Po- x + x + x = Po+ x x Pt Po
k = t PP x 0 0 log 303 . 2 k = T P PP t log2 0 0 303 . 2 where
P0 = Initial partial pressure of A
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Kinetics Of Some Miscelleneous Reactions
(i) Parallel Reactions :- here both the side reactions are of first order.
at any time t , A B C ( A - x ) X X
Let us assume the initial concentration of A is ‘a’ and after time t ‘x’ of it decomposes to form B and C.So we can write
Rate of diappearence of A = Rate of formation of B + rate of formation of C ) ( ) ( 2 1 a x k a x k dt dx =(k 1+k2) (a-x) ) ( ) (adx x k1 k2 t ) ( ln 1 ) ( ) ( ) ( ln 1 2 1 2 x a a t k k t k k x a a
Here , (K1 + K2) = Kav. and
2 1 ] [[ ] k k C B So, % Yield of B = 100 2 1 1 K K K % Yield of C = 1 2 100 2 K K K [A] = K k t o e A ] ( 1+ 2) [ ; [B] = [+ ](1 + ) ) 2 1 0 1 e k1 k2t k kk A - -( ; [C] = + ( ) ] [ + ) 2 1 0 2 e k1 k2t k kk A 1- -(
(ii) Reversible reaction
Consider the reaction where both the forward and backward reac-tions are of first order.
A kf kb B
At time t = 0 a b
At time t = t a – x x At time t = teq a – xeq xeq
Rate of the forward reaction = Kf(a-x) Rate of the backward reaction = Kbx at equilibrium ,
Rate of forward reaction = Rate of backward reaction Kf(a-x) = Kbx eq eq x a x = b f k k
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Now net rate of formation of B dxdt = Kf(a-x)- Kbx Substituting the value of Kb and on integrating we get
(kf + kb) = x x x t eq eq ln 1
(iii) Consecutive Reaction
A k1 B k2 C
Here we can write that ,
Rate of formation of B = Rate of disappearence of A - rate of formation of C [A]t = A e k1t 0 ] [ ; [B] t = ( ) ] [ 1 2 0 1 k k A k
e
k1t
e
k2t
[C]t = [A0] – ( [A] + [B] ) tmax = 2 21 1 l ) (k 1k n kk ; [B]max = [A0]. 1 2 2 2 1 k k k k k [C] [B] [A] • conc. timeIn this reaction the concentration of B will first reach to a mximum and than decreases as initially the rate of formation of B is greater than rate if its decomposition.
(iv) Pseudo First Order Reactions: These are the reactions which doesn’t appear to be first order but are actually of first order. in these types of reaction one of the reactants is present in excess, so it is not included in rate law and the rate of reaction does not depend on the concentration of that reactant.Consider the hydrolysis of ester
CH3COOC2H5 + H2O H CH
3COOH + C2H5OH
Here water is taken in excess so its concentration doesn’t changes much and therefore it is not included in the rate law .
Rate = k [CH3COOC2H5]
Intially the reaction appears to be of the second order but the reaction actually is of first order and therefore is called a pseudo first order reaction. For a pseudo first order reaction we can apply the kinetics of the first order.
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METHODS OF DETERMINATION OF ORDER OF REACTIONS : A few methods commonly used are given below :
1. Hit & Trial Method : It is method of using integrated rate equations, where the experimentalvalues of a, x & t are put into these equations. One which gives a constant value of k for different sets of a, x & t correspond to the order of the reaction.
2. Graphical Method : In this method graphs are plotted between the concentration of reactants and time
(i) A plot of [At] Vs ‘t’ gives a straight line for a zero order reaction.
[A] conc.
time
(i) A plot of log [At] versus 't' gives a straight line for the First order reaction.
In [A]t
t
(ii) A plot of (a – x)– (n–1) versus 't' gives a straight line any reaction of the order n (except n = 1).
3 . Half Life Method : The half life of nth order reaction is
n
a
t
12
1
(
)
, Where n is the order of the reaction So, n a a t t 1 2 1 2 2 / 1 1 2 / 1 ) ( ) (By experimental observation of the dependence of half life on initial concentration we can determine n, the order of reaction.
n = 1 + 2 0 1 0 1 2 / 1 2 2 / 1 ) log( ) log( ) log( ) log( a a t t .
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4. By the unit of rate constant :
The unit of rate constant for an ‘nth’order reaction is 1 ) 1 ( sec n Litremol For zero order reaction the unit will be mol L-1sec-1.
For first order reaction the unit of rate constant is sec-1.
For second order reaction the unit of rate constant is Lmol-1sec-1.
DEPENDENCE OF RATE CONSTANT ON TEMPERATURE(Arrehnius Equation)
According to Arrhenius hypothesis :
(i) Among all the reactant molecules only a certain number of molevules participate in a chemical reaction which are known as active molecules and the rest are known as passive molecules.
(ii) there exist an equillibrium between active and passive molecules and when temperature is increased the active molecules are converted into passive molecules by absorbing energy.
Active molecules Passive molecules
The temperature dependence of rate constant can be explained on the basis of Arrhenius equation:
k = A. eRTEa
Where A is Arrhenius constant or frequency factor or pre-exponential factor and is characteristic
of a reaction.
R Universal gas constant
Ea Activation energy (in J/Mol-1)
Straight from NCERT
* In the Arrhenius equation eRTEa is the fraction of molecules that have
kinetic energy greater than activation energy . Using k = A. eRTEa
A RTE
k a ln
ln
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let at temperature T1 rate constant be K1 and temperature T2 rate constant be K2, than A RTE k Ae k RTEa ln a ln 1 1 1 1
&
k Ae RT k RTEa A Ea ln ln 2 2 2 1 on solving we get log 2 1 1 2 1 1 303 . 2 E R T T k k aTemperature coefficient(
)
The temperature coefficient of a chemical reaction is defined as the ratio of the reat of reaction two temperatures differing by 10°C.
Temperature coefficient() = t t k k 10 .
Generally for every 100C rise in temperature the rate of reaction becomes by twice or thrice , therefore the value of temperature coefficient lies between 2 & 3.
This change in reaction rate can be explained on the basis of distribution curve proposed by Boltzman and Maxwell. They plotted the kinetic energy with fraction of molecules
T E
N N
( Where NE number of molecules with energy E and NT total number of molecules).
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Let the temperature coefficient of a reaction be ‘’ when temperature is
increased from T1 to T2 than the ratio of rtae constants can be calculated as 10 ) ( 2 1 2 2 ( )T T T T K k COLLISION THEORY
According to this theory , the reactant molecules are assumed to be hard spheres and a reaction will occurr only if the molecules collide with each other.
Not all collisions result in product formation, those collisions which result in product formation are known as Effective Collisions.For a collision to be effective following two barrier has to be crossed
(i) Energy Barrier (ii) Orientation Barrier
(i) Energy Barrier :- For an effective collision to occurr the colliding reactant molecules must have kinetic energy greater than the activation energy.
F ra c ti o n o f m o le c u le s Energy
Fraction of molecules having energy greater than activation energy and can prdouce effective collisions
A collision between high energy molecules overcomes the force of repulsion and forms an unstable activated complex which has maximum energy and is highly unstable.This activated than breaks into products or reactants. Thershold Energy(ET) :- The minimum energy which the reactant molecules must have in order to form products in a chemical reaction is called Threshold Energy .
Activation Energy (Ea) :- The extra energy which the reactant molecules
require to collide effectively and form products in a chemical reaction is called activation energy . Here,
Eaf Activation energy of forward reaction Eab Activation energy of backward reaction
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Ea Eb ETE
RE
p R eactants Pro duct R eactio n C o-ordinates E ne rg yOverall activation energy of reaction = Eaf-Eab = H
(ii) Orientation Barrier :- For a collision to be effective the reactant molecules must collide with proper orientation, such that they cover the maximum surface area of each other.
ADD DIAGRAM FROM NCERT
Thus in collision theory Activation energy and proper orientation together determine the criteria for an effective collision and the rate of chemical reaction.
There are two factors on which the rate of reaction depends:
(i) Collision Frequency (ii) Activation energy
Collision Frequency(Z) :- The number of collisions per second per unit volume of the reaction mixture is known as collision frequency.
For a reaction A + B Products
The rate of reaction can be written as rate = ZAB RT Ea
e
Where, ZAB is the collision frequency and RT Ea
e
is the fraction of molecules having energy equal to or greater than Ea.
REACTION MECHANISM
The mechanism of a reaction is the path through which the conversion of reactants take place into products.
The reaction mechanism could consist of several steps . these steps can be fast and slow reactions. We are concerned with the slowest reaction which we call RDS (Rate Determining Step) , because we can observe the change in concentration of reactants and products only for slow reactions.
To determine the order of the reaction we will first write the rate law for the RDS and if the RDS consist of any intermediate specie we will eleminate it .
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following two methods can be used to determine the rate law for a multistep reaction
(i) By equilibrium Consideration
consider the following mechanism for the reaction 2O3(g) 3O2(g)
Mechanism :
Step-1 O3(g) kf kb
O2(g) + O(g) fast
step-2 O(g) + O3(g) k2 2O2(g) slow
Since step-2 is the RDS so the rate law will be : Rate = k [O] [O3]
but here [O] is the intermediate and it can not be included in the rate law so we have to eleminate it therefore for the step -1
equilibrium constant (Kc) = b f k k = [ ] [ [ ]] ] [ ] ][ [ 2 3 3 2 O O K O O O O c
So the rate law will be rate = ' 3 2 2 1
2 2 3 [ ] [ ] ] [ ] [ . k O O O O k k c
Hence the order of the reaction is = 2+(-1) = 1 (ii) By Steady State Approximation
Here we assume that the concentration of the intermediate is constant under steady state condition so its rate of formation/ disappearence is zero.
Consider the reaction NO2(g) + CO (g) CO2(g) + NO(g) The reaction mechanism can be given as
step 1 : NO2 + NO2 k1 NO + NO3 (fast ) step 2 : NO3 + CO k2 CO2 + NO2 ( slow)
Since , NO3 is the intermediate , from steady state approximation we can say that d[dtNO3] = o
But d[dtNO3] = k
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So, [NO3] = [[ ]] 2 2 2 1 CO NO kkrate of reaction = rate of disappearence of NO2 rate =d[dtNO2]= k
1[NO2]2 + k2[NO3][CO] = k1[NO2]2 + k 2 [[ ]] 2 2 2 1 CO NO k k [CO] rate = 2k1[NO2]2
So, the order of the reaction is 2.
Types of reactions on the basis of influence of temperature Effect of presence of a catalyst
Rate constant in presence of catalyst RT E p
p
Ae k Rate constant in absence of catalyst ka AeRTEa
So, RT E E a p e a p k k ( )
Ea Activation energy in absence of catalyst Ep Activation energy in presence of catalyst
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BOOST YOUR BASICS
Q.1. For the equation 2NO + 2H2N2+ 2H2O, write the most probable rate law from the follow ing data. What is the order of reaction? Also calculate rate constant.
Experiment [NO] [H2] Rate (mol L-1s-1)
I 0.2 0.2 3 × 10-3
II 0.4 0.2 1.2 × 10-2
III 0.2 0.4 6 × 10-3
Q.2. For the reaction OCl-+ I-+ OH- OI-+ Cl-+ H
2O kinetic data are given below. Calculate rate law
and value of rate constant.
Exp. No. [OCl–] [I–] [OH–] d[IO ]
dt
(mol dm-3) (mol dm-3) (mol dm-3) (mol dm-3) (s-1)
1. 0.0017 0.0017 1.0 1.75×10-4
2. 0.0034 0.0017 1.0 3.5×10-4
3. 0.0017 0.0034 1.0 3.5×10-4
4. 0.0017 0.0017 0.5 3.5×10-4
Q.3. According to the reaction Cr2O72-+ 5H++ 3HNO
2 2Cr
3+ + 3NO 3
-+ 4H
2O The rate of
disappearance of Cr2O72-is found to be 2.4 × 10-4 mole L-1s-1. Find the rate of appearance of
Cr3+during given time interval.
Q.4. Fill in the blanks in the following table which treats reaction of a compound A with a compound B, that is of the first order with respect to A and zero order with respect to B.
Expt. No. [A] (mol L-1) [B] (mol L-1) Initial rate (mol L-1 s-1) 1. 0.1 0.1 20 × 10-2 2. ---- 0.2 4.0 × 10-2 3. 0. 4 0. 4 ---4. ---- 0.2 2.0 × 10-2
Q.5. The reaction 2NO + O2 2NO2, follows the rate law = k[NO]2[O
2]. What is the order of the
reaction?If k = 2.0×10–6 mol–2 L2s–1, what is the rate of the reaction when [NO] = 0.04 mol L–1 and
[O2] = 0.2 mol L–1 ?
Q.6. From the following data of initial concentrations and rates, calculate the order of reaction
aA Products; and its rate constant.
[A] mol L–1 0.1 0.2 0.4
Rate mol L–1 s–1 9 × 10–5 36×10–5 144 × 10–5
Q.7. For a reaction aA + bB mM + nN, the rate of reaction is given as k[A]x[B]y
Calculate the order of the reaction and the rate constant from the given initial concentrations and the corresponding rates.
[A] mol L–1 0.1 0.1 0.2
[B] mol L–1 0.2 0.4 0.2
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Q.8. The data given in the following table pertain to the reaction, 2A + B C
Determine the form of the rate equation and the value of the rate constant Initial concentration (mol L-1) Expt. No. [A] [B] Initial rate (mol L-1 s-1) 1. 1 × 10-3 1 × 10-3 7 × 10-6 2. 1 × 10-3 2 × 10-3 14 × 10-6 3. 1 × 10-3 3 × 10-3 21 × 10-6 4. 2 × 10-3 3 × 10-3 84 × 10-6
Q.9. The following initial rate data were obtained for the reaction : 2NO(g) + Br2(g) 2NOBr(g)
Run [NO]/M [Br2]/M Rate/M min-1
1. 1.0 1.0 1.30 × 10-3
2. 2.0 1.0 5.20 × 10-3
3. 4.0 2.0 4.16 × 10-2
Determine the reaction rate law and the value of the rate constant.
Q.10. For the reaction AB, it was found that the concentration of B increased by 0.3 mol L–1 in
2 hours. What is the average rate of reaction ?
Q.11. In the reaction XY, the initial concentration of X is 2.5 mol L–1 and its concentration after
3 hours is 0.7 mol L–1. What is the average rate of the reaction ?
Q.12. When ammonia is treated with O2 at elevated temperaturs, the rate of disappearance of ammonia is found to be 3.5×10–2 mol dm–3s–1 during a measured time interval. Calculate the
rate of appearance of nitric oxide and water.
Q.13. In a reaction N2O5 2NO2 + 1
2O2, the rate of disappearance of
N2O2 is 6.5 × 10–3 mol L–1 s–1. Compute the rates of formation of NO
2 and O2.
Q.14. The following reaction was carried out at 44°C : N2O2 2NO2 + 1/2O2
The concentration of NO2 is 6.0 × 10–3 M after 10 minutes of the start of the reaction.
Calculate the rate of production of NO2 over the first ten minutes of the reaction.
Q.15. The rate of a particular reaction doubles when temperature changes from 27° C to 37°C. Calculate the energy of activation for such reaction. (R = 8.314 J K–1 mol–1)
Q.16. The rate constant of a reaction is 2 × 10–2 s–1 at 300 K and 8 × 102s–1 at 340 K. Calculate the
energy of activation of the reaction.
Q.17. For a chemical reaction the energy of activation is 85 kJ mol–1. If the frequency factor is
4.0 × 109 L mol–1 s–1, what is the rate constant at 400 K ?
Q.18. The energy of activation of a reaction is 140 kJ mol–1. If its rate constant at 400 K is
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Q.19. Calculate the ratio of the catalysed and uncatalysed rate constant at 20° C if the energy of activation of a catalysed reaction is 20 kJ mol–1 and for the uncatalysed reaction is 75 kJ
mol–1.
Q.20. The decomposition of methyl iodide, 2CH3I(g) C2H6(g) + I2(g)
at 273° C has a rate constant of 2.418 × 10–5 s–1. If activation energy for the reaction is
+179.9 mol–1, what is the value of collision factor 'A' at 273°C ? Q.21. The reaction,
2N2O5 2N2O4 + O2
occurs in carbon tetrachloride. The rate constant is 2.35×10–4 sec–1 at 30°C. Calculate the
activation energy of the reaction.
Q.22. For the inversion of cane sugar,
C12H22O11 + H2O C5H12O6 + C6H12O6
the rate constant is 2.12 × 10–4 L mol–1sec–1 at 27°C. The activation energy of the reaction is
1.07 × 105 J mol–1. What is the rate constant of the reaction at 37° C ?
Q.23. For a first order reaction, the rate constant is 0.1 s–1. How much time will it take to reduce
the concentration from initial value of 0.6 mol L–1 to 0.06 mol L–1 ?
Q.24. A substance decompose following first order reaction. If the half life period of the reaction is 35 minutes, what is the rate constant of this reaction ?
Q25. For a certain first order reaction, it take 5 minutes for the initial concentration of 0.6 mol L–1 to become 0.2 mol L–1. What is the rate constant for this reaction ? [log 3 = 0.4771] Q.26. Find the two -thirds life (t2/3) of a first order reaction in which k = 5.48 × 10–1 sec–1 . Q.27. A first order reaction has a specific rate of 10–3sec–1. How much time will it take from 10 g
of the reactant to reduce to 7.5 g (log 2 = 0.3010; log 4 = 0.6020 and log 6 = 0.7782) ?
Q.28. In a reaction 5 g ethyl acetate is hydrolysed per litre in presence of dilute HCl in 300 min. If the reaction is of first order and initial concentration is 22 g per litre, calculate the rate constant for the reaction.
Q.29. Calculate the half life of the reaction A B, when the initial concentration of A is 0.01 mol L–1 and initial rate is 0.00352 mol L–1 min–1. The reaction is of the first order.
Q.30. In reaction A B + C, the following data were obtained:
t in seconds 0 900 1800
Concentration of A 50.8 19.7 7.62
Prove that it is a first order reaction.
Q.31. The first order reaction has k = 1.5 × 10–6 per second at 200°. If the reaction is allowed to
run for 10 hours at the same temperature, what percentage of the initial concentration would have changed into the product ? What is the half life period of this reaction ?
Q.32. A first order reaction is 20% completed in 10 minutes. Calculate (i) the specific rate con stant of the reaction and (ii) the time taken for the reaction to go to 75% completion.
Q.33. The rate constant of a reaction with respect to reactant A is min–1. If we start with [A] = 0.8
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Q.34. What will be the initial rate of a reaction if the constant is 10–3 min–1 and the concentration is
0.2 mol dm–3?How much of the reactant will be converted into the product in 200 minutes ? Q.35.. A substance A decomposes by the first order reaction. Starting initially with [A] = 2.00 M,
after 200 minutes [A] = 0.25M. For this reaction what is t1/2 and k ?
Q.36. In this case we have 2A3B + C Time t Total pressure of A + B+C P2 P3 Find k. Q.37. A2B + 3C Time t Total pressure of ( B+C) P2 P3 Find k. Q.38. A2B + 3C Time t Volume of reagent V2 V3
Reagent reacts with all A, B and C. Find k. [Assuming n-factor of A, B & C are same]
Q.39. k1 = x hr–1; k
1 : k2 = 1 : 10. Calculate [A]
] C [
after one hour from the start of the reaction. Assuming only A was present in the beginning.
Q.40. How much time would be required for the B to reach maximum concentration for the reaction . A k1 B k2 C. Given k 1 = 4 2 n l , k2 = 2 2 n l .
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Insight to the concepts Q.1. The reaction
cisCr(en)2(OH)+
2 transCr(en)2(OH) +
2
is first order in both directions. At 25°C the equilibrium constant is 0.16 and the rate constant k1 is 3.3 × 10 4s 1. In an experiment starting with the pure cis form, how long would it take for half the equilibrium amount of the trans isomer to be formed ?
Q.2. Two reations (i) A products (ii) B products, follow first order kinetics. The rate of the reaction (i) is doubled when the temperature is raised from 300 K to 310K. The half life for this reaction at 310K is 30 minutes. At the same temperature B decomposes twice as fast as A. If the energy of activation for the reaction (ii) is half that of reaction (i), calculate the rate constant of the reaction (ii) at 300K.
Q.3. The half life for a reaction between fixed concentration of reactants veries with temperature as follows :
t°C 520 533 555 574
t1/2 sec 1288 813 562 477
Calculate the activation energy of this reaction.
Q.4. What percentage of reactant molecules will crossover the energy barrier at 325 K ? Heat of
reaction is 0.12 kcal and activation energy of backward reaction is 0.02 kcal.
Q.5. A decomposition reaction has following mechaism
2N2O5 4NO2+ O2 (overall)
(i) N2O5 NO2 + NO3 (Fast decomposition) (ii) NO2 + NO3 NO + NO2 + O2 (slow)
(iii) NO + NO3 2NO2 (fast)
Determine rate law and the order of reaction.
Q.6. For the system A(g) B(g),H for the forward reaction is –33 kJ/mol (Note :H =E in this case). Show that equilibrium constant K = [B][A] = 5.572 × 105 at 300 K. If the activation energies Ef & Eb are in the ratio 20 : 31, calculate Ef and Eb at this temperature. Assume that the pre-exponential factor is the same for the forward and backward reactions.
Q.7. The half life period for the reaction N2O5 2NO2+ 1
2O2is 2.4 hrs. a 30
oC. What time would be
required to reduce 5 × 1010molecules of N
2O5to 10
8molecules ? .
Q.8. 10 gram atoms of an -active radio isotope are disintegating in a sealed container. In one hour the helium gas collected at STP is 11.2 cm3. Calculate the half-life of the radio-isotope.
Q.9. In a reaction, aA products, the rate is doubled when the concentration of A is increased 4 times. If 50 % of the reaction occurs in 1414s, how many seconds would it take for the completion of 75% reaction?
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Q.10.Mechanism for the reaction 2A C is given as follows. (i) A + A k1 A* + AA (Activation)
(ii) A* + A k2 A + AA (Deactivation) (iii) A* k3 C (Reaction)
Deduce general rate law for the reaction, using steady state approximation.
Q.11 (a) The decomposition of HI to I2at 508oC has a half-life of 135 minutes when P
HI= 0.1 atm
(initial) which comes down to one-tenth of that value when the initial pressure is 1 atm. Calculate the rate constant.
Q.12 Above 500oC, the reaction NO
2+ CO CO2+ NO obeys the rate law rate = k[NO3][CO]. Below
500oC the rate law for this reaction is rate = k[NO 2]
2. Suggest mechanism for each of the cases
Q.13. Decomposition of non-volatile solute 'A' into another non-volatile solute B and C, when dis-solved in water follows first order kinetics as:
A 2B + C
When one mole of A is dissolved in 180 gm of water and left for decomposition, the vapour pressure of solution was found to be 20 mm Hg after 12 hrs. Determine the vapour pressure of the solution after 24 hrs. Assume constant temperature of 25°C, throughout. The vapour pressure of pure water at 25°C is 24 mm Hg. [Give your answer by adding all the digits ]
Q.14. Consider a reversible reaction :
A
k1 k2
B
Which is a first order in both the directions (k1 =
3 38 . 1
× 10–2 min–1). The variation in concentration
is plotted with time as shown below.
0.1 0 0.2 0.3 [A] [B] time conc. (M)
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OBJECTIVES Q.1 A zero order reaction is
one-(A) In which reactants do not react (B) In which one of the reactants is in large excess (C) Whose rate does not change with time (D) Whose rate increase with time
Q.2 If concentration are measured in mole/li9tre and time in minutes, the unit for the rate constant of
a 3rdorder reaction are
(A) mol lit-1min-1 (B) lit2mol-2min-1 (C) lit mol-1min-1 (D) min-1
Q.3 Following reaction was carried out at 300 K. 2SO2(g) + O2(g)2SO3(g) How is the rate of formation of SO3related to the rate of disappearance of O2?
(A) – [O ]2 t = + 1 2 3 [SO ] t (B) – 2 [O ] t = 3 [SO ] t (C) – [O ]2 t = – 1 2 3 [SO ] t (D) None of these
Q.4 According collision theory of
reaction-(A) Every collision between reactiont molecules leads to a chemical reaction. (B) Rate of reaction is proportional to the velocity of the molecules
(C) Rate of reaction is proportional to the average energy of the molecules (D) Rate of reaction is proportional to the number of collision per second.
Q.5 Which of the following rate laws has an overall order of 0.5 for the reaction, A + B + C
product-(A) R = k[A].[B].[C] (B) R = k[A]0.5[B]0.5[C]0.5
(C) R = k[A]1.5[B]-1[C]0 (D) R = k[A] [B]0[C]0.5
Q.6 For the system A2(g) + B2(g)
2AB(g),
H
=–160 kJ If the activation energy for the forwordstep is 100 kcal/mol. What is the ratio of temperature at which the forword and backward reaction shows the same % change of rate constant per degree rise of temperature ? (1 cal = 4.2 J)
(A) 0.72 (B) 0.84 (C) 0.42 (D) 1
Q.7 The t1/2of first order reaction is 10 minutes. Starting with 100 grams/lit of the reaction, the amount remaining after one hour is
(A) 25.0 g (B) 3.130 g (C) 12.50 g (D) 1.563 g
Q.8 For the reaction, 2NON2+ O2, the experssion - 1
2
d[NO]
dt represents
(A) The rate of formation of NO (B) The average rate of the reaction (C) The instantaneous rate reaction (D) All the above
Q.9 For a reaction of the type 2A + B 2C, the rate of the reaction is given by k[A]2[B]. When the
volume of the reaction vessel is reduced to 1/4 th of the original volume, the ratev of reaction by a factor of
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Q.10 What is order withrespect to A, B, C respectively
[A] [B] [C] rate(M/sec.) 0.2 0.1 0.02 8.08×10-3 0.1 0.2 0.02 2.01×10-3 0.1 1.8 0.18 6.03×10-3 0.2 0.1 0.08 6.464×10-2 (A) –1,1, 3/2 (B) –1,1, 1/2 (C) 1, 3/2, –1 (D) 1, –1, 3/2 Q.11 For reaction, rate = k[A] [B]2/3the order of reaction
is-(A) 1 (B) 2 (C) 5/3 (D) Zero
Q.12 The elementary reaction A + B products, has k = 2 × 10-5M-1s-1at a temperature of 27oC. Severl
experimentary runs carried out using stoichiometric proportion. The reaction has a temperature corfficient value of 2.0. At what temperature should the reaction be carried out if inspite of halving the concentrations, the rate of reaction is desired to be 50% higher than a previous run. (Given
n6 n2
= 2.585)
(A) 47oC (B) 53oC (C) 57oC (D) 37oC
Q.13 According to collision
theory-(A) All collisions are sufficiently violent (B) All collisions are responsible formation. (C) All colisions are effective.
(D) Only a fraction of collisions are effective which have enough energy to form products.
Q.14 When the temperature of a reaction increases from 270C to 370C, the rate increases by 2.5 times,
the activation energy in the temperature range is
(A) 53.6 kJ (B) 12.61 kJ (C) 7.08 kJ (D) 70.8 kJ
Q.15 For the reaction R – X + OH– ROH + X–The Rate is given as Rate = 5.0 × 10-5[R – X][OH–] +
0.20 × 10-5[R–X] what percentage of R – X reacted by SN2 mechanism when [OH-] = 1.0 × 10 -2M
(A) 96.1% (B) 3.9% (C) 80% (D) 20%
Q.16 Which of the following curves represents a Ist order
reaction-(A) (B) (C) (D)
Q.17 The rate of a reaction increases 4-fold when conecentration of reaction is increased 16 times. If
the rate of reaction is 4 × 10-6mole L-1when concentration of the reaction is 4 × 10-4mole L-1, the
rate constant of the reaction will be
(A) 2 × 10-4mole1/2L-1/2sec-1 (B) 1 × 10-2sec-1
(C) 2 × 10-4mole-1/2,L1/2sec-1 (D) 25 mole-1Lmin-1
Q.18 If 'a' is the intial concentration of a substance which reacts according to zero order kinetic and k
rate conatant, the time for the reaction to go to completion
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Q.19 The following data are obtained from the decomposition of a gaseous compound
Initial pressure, (atm) 1.6 0.8 0.4
Time for 50% reaction,(min) 80 113 160
The order of the reaction is
(A) 1.0 (B) 1.5 (C) 2.0 (D) 0.5
Q.20 For a given reaction the concentration of the reactant plotted against time gave a straight line
negative slope. The order of the reaction
is-(A) 3 (B) 2 (C) 1 (D) 0
Q.21 The rate constant of a first order reaction is generally determined from a plto of
(A) Concentration of reactant vs time t (B) log (concentration of reaction) vs time t
(C) 1
concentration of reaction vs time t (D) Concentration of reactant vs log time t
Q.22 Which of the following correctly represents the variation of the rate of the reaction with
tempera-ture ?
(A) (B)
(C) (D)
Q.23 The plot of log K versus 1
Tis linear with a slope of
(A) Ea R (B) a E R (C) Ea 2.303R (D) a E 2.303R
Q.24 According to the collision theory, the rate of reaction increases with temperature due
to-(A) Greater number of collision
(B) Higher velocity of reacting molecules
(C) Greater number of molecules having the activation energy (D) Decrease in the activation energy
Q.25 If a reaction A + B C is exothermic to the extent of 30 kJ/mol and the forward reaction has an activation energy 70 kJ/mol, the activation energy for the reverse reaction is
(A) 30 kJ/mol (B) 40 kJ/mol (C) 70 kJ/mol (D) 100 kJ/mol
Q.26 A first order reaction takes 40 min for 30% decomposition. Calculate t1/2.
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Q.27 For a certain reaction involving a single reaction, it is found that C0 T is constant where C0is the initial concentration of the reaction and T is the half-life. What is the order the reaction ?
(A) 1 (B) Zero (C) 2 (D) 3
Q.28 The high temperature (1200K) decomposition of CH3COOH(g) occurs as follows as per
simul-taneous 1storder reactions.
CH3COOH k1 CH
4+ CO2
CH3COOH k 2 CH
2CO + H2O
What would be the % of CH4 by mole in the product mixture (excluding CH3COOH) ?
(A)
1
1 2 50k k k (B)
1 1 2 100k k k (C)
1 1 2 200k k k (D) it depends on timeQ.29 The number of half-lives (t1/2) required to bring the ratio to
0 N N = 0.125 from 0 N N = 1 of a radioactive element is (A) 2 (B) 4 (C) 3 (D) 1
Q.30 The reaction, A(g) + 2B(g)C(g) + D(g) is an elementary process. In an experiment, the initial partial pressure of A and B are PA= 0.60 and PB= 0.80 atm. When PC= 0.2 atm the rate of reaction relative to the initial rate is
(A) 1/48 (B) 1/24 (C) 9/16 (D) 1/6
Q.31 Half life period for a first order reaction is 20 minutes. How much time is required to change the
concentration of the reactants from 0.08M to 0.01 M
(A) 20 minutes (B) 60 minutes (C) 40 minutes (D) 50 minutes
Q.32 The kinetic datas for the reaction: 2A + B22AB are as given below:
[A] [B] Rate
mol L-1 mol L-1 mol L-1min-1
0.5 1.0 2.5 × 10-3
1.0 1.0 5.0 × 10-3
0.5 2.0 1 × 10-2
The order of reaction w.r.t. A and B2are, respectively,
(A) 1 and 2 (B) 2 and 1 (C) 1 and 1 (D) 2 and 2
Q.33 If for any reaction rate constant is equal to the rate of the reaction at all conaentrations, the order
is-(A) 0 (B) 2 (C) 1 (D) 3
Q.34 For the irreversible unimolecular type reaction A kproducts, in a batch reactor, 80% reactant
A(CA0= 1 mole/lit.) is converted in a 480 second run and conversion is 90% after 18 mintue. The order of this reaction
is-(A) 1 (B) 2 (C) 1/2 (D) 3/2
Q.35 The rate constant, the activation energy and the Arrhenius parmeter of a chemical reaction at 25oC
a r e
3.0 × 10-4s-1, 104.4 kJ mol-1and 6.0 × 1014s-1respectively.The value of the rate constant as T
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(A) 2.0 × 1018s-1 (B) 6.0 × 1014s-1 (C) (D) 3.6 × 1030s-1
Q.36 For the first order reaction t99%= x × t90%the value of 'x' will
be-(A) 10 (B) 6 (C) 3 (D) 2
Q.37 The gas phase decomposition 2N2O54NO2+ O2follows the first order rate law with rate
con-s t a n t
K = 7.5 × 10-3sec-1. The initial pressure of N
2O5is 0.1atm. The time of decomposition of N2O5so
that total pressure becomes 0.15 atm will
be-(A) 54 sec (B) 5.4 sec (C) 3.45 sec (D) 34.55 sec
Q.38 If in the fermentation of sugar in an enzymatic solution that is 0.12 M, the concentration of the
sugar is reduced to 0.06 M in 10h and to 0.03 M in 20h, what is the order of the
reaction-(A) 1 (B) 2 (C) 3 (D) 0
Q.39 In a Istorder reaction, A products, the concentration of the reactant decreases to 6.25% of its
initial value in 80 minutes. What is the rate constant reaction 100 minutes after the starts, if the initial concentration is 0.2 mole/litre ?
(A) 2.17 × 10-2min-1 (B) 3.465 × 10-2min-1
(C) 3.465 × 10-3min-1 (D) 2.166 × 10-3min-1
Q.40 For the first order reaction A(g) 2B(g)+ C(g), the initial pressure is PA = 90 mm Hg, the pressure after 10 minutes is found to be 180 mm Hg. The rate constant of the reaction is
(A) 1.15 × 10-3sec-1 (B) 2.3 × 10-3sec-1
(C) 3.45 × 10-3sec-1 (D) 6 × 10-3sec-1
Q.41 For a certain reaction the variation of the rate constant with temperature is given by the equation
In kt= 1n k0+ 1n3
10
t (t0oC) The value of the temperature coefficient of the reaction rate is
therefore-(A) 4 (B) 3 (C) 2 (D) 10
Q.42 A catalyst lowers the activation energy of a reaction from 20 kJ mole-1to 10 kJ mole-1. The
tem-perature at which the uncatalysed reaction will have the same rate as that of the catalysed at 27oC
is
(A) –123oC (B) 327oC (C) 1200oC (D) +23oC
Q.43 The rate of reaction triples when temperature changes from 20oC to 50oC. Calculate energy of
activation for the reaction.
(A) 28.81 kJ mol-1 (B) 38.51 kJ mol-1
(C) 18.81 kJ mol-1 (D) 8.31 kJ mol-1
Q.44 The half life time for the decomposition of a substance dissolved in CC14is 2.5 hour at 30oC. How
much of the substance will be left after 10 hours, if the initial weight of the substance is 160 gm ?
(A) 20 gm (B) 30 gm (C) 40 gm (D) 10 gm
Q.45 For the reaction [Cr(H2O)4C12]+
(aq.) 1 k [Cr(H2O)5C1]2+ (aq.) 2 k [Cr(H2O)6C1]3+ (aq.) K1= 1.78 × 10-3s-1 and k 2= 5.8 × 10 -5s-1
If initial concentration of [Cr(H2O)4C12]+is 0.0174 M at 273 K. Calculate time at which
concen-tration of [Cr(H2O)5C1]2+is maximum.
(A) 1990 seconds (B) 1090 seconds
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Q.46 What is the activation energy for the decomposition of N2O5 as N2O5 2NO2+ (1/2) O2If the value of the rate constant are 3.45 × 10-5and 6.9 × 10-3at 27oC and 67oC respectively.
(A) 102 × 102kJ (B) 488.5 kJ (C) 92 kJ (D) 112.3 kJ
Q.47 If for a first order reaction, rate constant varies with temperature according to the
graph given below. At 27oC, 1.5 × 10-4percent of the reaction molecules are
able to cross-over the potential barrier. At 52oC, the slope of this graph is
equal to 0.2 K-1sec-1, calculate the value of rate constant at 52oC, assuming
that activation energy does not change in this temperature range. (A) 3.14×10-2min-1 (B) 1.35 × 10-2min-1
(C) 0.75 × 10-2min-1 (D) 8.75 × 10-2min-1
Q.48 the rate constant for a first order reaction is 60s-1. How much time will it take to reduce the initial
concentration of the reactant to its 1/16th
value-(A) 0.046 s (B) 0.46 s (C) 0.124 s (D) 2.123 s
Q.49 1 mole of gas changes linearly from initial state (2 atm, 10 lt) to final state (8 atm, 4 lt). Find the
value of rate constant, at the maximum temperature, that the gas can attain. Maximum rate con-stant is equal to 20 sec-1and value of activation energy is 40 kJ mole-1, assuming that activation
energy does not change in this temperature range.
(A) 0.56 × 10-3sec-1 (B) 3.16 × 10-3sec-1
(C) 1.56 × 10-3sec-1 (D) 5.12 × 10-3sec-1
Q.50 A first order reaction was started with a decimolar solution of the reactant. After 8 minutes and 20
seconds, its concentration was found to be M/100. Determine the rate constant of the reaction. (A) 4.6 × 10-3sec-1 (B) 16.6 × 10-3sec-1
(C) 24.6 × 10-3sec-1 (D) 40.6 × 10-3sec-1
Q.51 87.5% of a radioactive substance disintegrates in 40 minutes. What is the half life of the substance
?
(A) 13.58 min (B) 135.8 min (C) 1358 min (D) None of these
Q.52 A gaseous substance AB3decomposes irreversibly according to the overall equation AB3 1
2A2
+ 3
2B2. Starting with pure AB3, the partial pressure of the reaction varies time for which the data
are given below.
Time in hours 0 5.0 15.0 35.0
3
AB
P mm Hg 660 330 165 82.5
What is the order of the reaction ?
(A) 2 (B) 0.5 (C) 1 (D) 1.5
Q.53 The inversion of cane sugar proceeds with half-life of 500 minute at pH 5 for any concentration of
sugar. However if pH = 6, the half-life changes to 50 minute. The rate law ecpression for the sugar inversion can be written as
(A) r = K[sugar]2[H]6 (B) r = K[sugar]1[H]0
(C) r = K[sugar]0[H+]6 (D) r = K[sugar]0ss[H+]1
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60 kJ mol-1. At what temperature would k be 1.5 × 104s-1?
(A) 12oC (B) 24oC (C) 48oC (D) 36oC
Q.55 Decomposition on NH3 on heated tungsten yields the following data :
Initial pressure (mm) 65 105 y 185
Half-life 290 x 670 820
What are the values of x and y in that order ?
(A) 420 s, 110 mm (B) 500 s, 160 mm
(C) 520 s, 170 mm (D) 460 s, 150 mm
Q.56 The half life period of gaseous substance undergoing thermal decomposition was measured for
various initial pressure 'P' with the following result.
P(mm) 250 300 400 450
t1/2(min) 136 112.5 85 75.5
Calculate the order of reaction.
(A) 2 (B) 4 (C) 6 (D) 10
Q.57 For the reaction 2N2O5(g) 4NO2(g) + O2(g), the concentration of NO2increases by 2.4 × 10-2
Mol
lit-1in 6 second. What will be the rate of appearance of NO
2and the rate of disappearance of N2O5.
(A) 2 × 10-3mol L-1sec-1, 4 × 10-3mol L-1sec-1 (B) 2 × 10-3mol L-1sec-1, 1 × 10-3mol L-1sec-1
(C) 2 × 10-3mol lit-1sec-1, 2 × 10-3mol lit.-1sec-1 (D) 4 × 10-3mol lit.-1sec-1, 2 × 10-3mol lit.-1sec-1
Q.58 The rate constant of a particular reaction has the dimensions of a frequency. What is the order of
the reaction ?
(A) Zero (B) First (C) Second (D) Fractional
Q.59 The reaction of iodomethane with sodium ethoxide proceeds as : EtO+ MeI EtOMe + 1. A plot of log
MeI
EtO
on the Y-axis against 's' on the X-axis gives a straight line with a positive slope. What is the order of the reaction ?
(A) Second (B) First (C) Third (D) Fractional
Q.60 For the reaction,C2H5I + OH-C
2H5OH + I
- the rate constant was found to have a value of
5.03×10-2mol-1dm3s-1at 289 K and 6.71 mol-1dm3s-1at 333 K. What is the rate constant at 305 K ?
(A) 1.35 mol-1dm3s-1 (B) 0.35 mol-1dm3s-1
(C) 3.15 mol-1dm3s-1 (D) 7.14 mol-1dm3s-1
Q.61 A plot of ln rate Vs ln C for the nth order reaction
gives-(A) a straight line with slope n and intercept ln kn. (B) a straight line with slope (n - 1)
(C) a straight line with slope ln knand intercept 'n' (D) a straight line with slope -n and intercept kn.
Q.62 The first order rate constant for a certain reaction increases from 1.667×10-6 s-1at 727oC to 1.667×10 -4s-1at 1571oC. The rate constant at 1150oC, assuming constancy of activation energy over to given
temperature range is
(A) 3.911 × 10-5sec-1 (B) 1.139 × 10-5sec-1
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Q.63 The solvolysis of 2-chloro-2-methyl propane is aqueous acetone : H2O + (CH3)3C - Cl HO -C(CH3)3+ H+Cl- has a rate equation. Rate = K[(CH
3)3C-Cl]. From this it may be inferred that the
energy profile of the reaction leading from reactants to products is
(A) (B)
(C) (D)
Q.64 Thermal decomposition of a compound is of first order. If 50 % of a sample of the compound is
decompound in 120 minutes, show how long will it take for 90 % of the compound to decompose ?
(A) 399 min (B) 410 min (C) 250 min (D) 120 min
Q.65 The rate constant of a certain first order reaction increases by 11.11% per degree rise of
tempera-ture at 27oC. By what % will it increases at 127oC, assuming constancy of activation energy over
the given temperature range ?
(A) 5.26% (B) 5.62% (C) 6.25% (D) 7.33%
Q.66 The half-life for radioactive decay of14C is 5730 y. An archaeogical artefact contained wood had
only 80% of the14C found in a living tree. Estimate the age of the sample.
[Radioactive decays follow the first order kinetic]
(A) 1657.3 y (B) 1845.4 y (C) 1512.4 y (D) 1413.1 y
Q.67 Two substance A and B are present such that [A0] = 4[B0] and half-life of A.is 5 minute and that of B is 15 minute. If they start decaying at the same time following first order kinetics how much time later will the concentration of both of them would be same.
(A) 15 minute (B) 10 minute (C) 5 minute (D) 12 minute
Q.68 The following data were obtained during the first order thermal decomposition of SO2Cl2at a constant volume. SO2Cl2(g) SO2(g) + Cl2(g)
Experiment Time/s Total pressure/atm
1 0 0.5
2 100 0.6
Calculate the rate of the reaction when total pressure is 0.65 atm. (A) 7.8 × 10-4s-1atm. (B) 0.8 × 10-4s-1atm.
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nce
Sir
SUBJECT APTITUDE
One or more than one choice may be correct :
Q.1 Bicyclo hexane was found to undergo two paeallel first order rearrangements, as given
below-Bicyclo hexane
Choose the correct
options-(A) % of cyclohexane = 77 (B) % of methylcyclopentance = 23 (C) % of methylcyclopentance = 77 (D) % of cyclohexane = 23
Q.2 Consider the following case of competing 1storder reaction.
After the start of the reaction at t = 0 with only A, the [C] is equal to the [D] at all times. The time in which all three concentrations will be equal is given by
(A) t = 1 1 n3 2k (B) t = 2 1 n3 2k (C) t = 1 1 n3 3k (D) t = 2 1 n3 3k
Q.3 At 25oC, the second order rate constant for the reaction I-+ ClO- IO3-+Cl-is 0.0606 M-1sec-1. If
a solution is initially 3.5 × 10-3M with respect to each reactants. Choose the correct options –
(A) concentration of A = 3.29 × 10-3M after 300 sec.
(B) concentration of B = 3.29 × 10-3M after 300 sec.
(C) concentration of A = 0.19 × 10-3M after 300 sec.
(D) None of these
Q.4 Which is correct graph :
(A) (B) n dc dt (C) n dc dt (D) 0.75 0.5 t t
Q.5 In a pseudo first order hydrolysis of ester in water, the following results were obtained :
t/s 0 30 60 90
