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CBSE Questions for Class 12 Engineering Chemistry Chemical Kinetics Quiz 15 - MCQExams.com

For the following first-order competing reaction:
A+Reagentproduct
B+ReagentProduct
the ratio of K1/K2, if only 50% of B will have been reacted when 94% of A has been reacted is
(log2=0.3,log30.48)
  • 4.06
  • 0.246
  • 8.33
  • 0.12
In the given first-order sequential reactions:
AK1BK2CK3D, what is the ratio of number of atoms of A to the number of atoms of B after long time interval starting with pure A?
(K1ln21200;K2=ln230)
  • 0.67
  • 10
  • 20
  • 40
Two reactions: (I) Aproducts and (II) Bproducts, follow first-order kinetics. The rate of reacion-I is doubled when temperature is raised from 300 to 310K. The half-life for this reaction at 310K is 30min. 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, the rate constant of reaction II at 300K is
  • 0.0233min1
  • 0.0327min1
  • 0.0164min1
  • 0.0654min1
Surface-catalysed reactions that are incorporated by the product, obey the differential rate expression, \cfrac { dy }{ dt } =\cfrac { k\left[ { C }_{ 0 }-y \right]  }{ 1+by } , where { C }_{ 0 }= initial concentration and k and b are constants. The half-life of reaction is 
  • \left( 1+{ C }_{ 0 }b \right) \ln { 2 } -\cfrac { { C }_{ 0 }b }{ 2 }
  • \left( 1-{ C }_{ 0 }b \right) \ln { 2 } +\cfrac { { C }_{ 0 }b }{ 2 }
  • \left( 1-{ C }_{ 0 }b \right) \ln { 2 } -\cfrac { { C }_{ 0 }b }{ 2 }
  • \left( 1+{ C }_{ 0 }b \right) \ln { 2 } +\cfrac { { C }_{ 0 }b }{ 2 } \quad
A substance undergoes first-order decomposition. The decomposition follows two parallel first-order reaction with { K }_{ 1 }=1.26\times { 10 }^{ -4 }{ s }^{ -1 } for the formation of B and { K }_{ 2 }=3.15\times { 10 }^{ -4 }{ s }^{ -1 } for the formation of C. The percentage distribution of B and C are
  • 29% B, 71% C
  • 75% B, 25% C
  • 90% B, 10% C
  • 60% B, 40% C
Rate of an uncatalyzed first-order reaction at T K is half of the rate of a catalyzed reaction at 0.5T T. If the catalyst lowers the threshold energy by 20\ kcal, what is the activation energy of the uncatalyzed reaction?
\left( T=300K,\ln { 2 } =0.7 \right)
  • 39.58\ kcal/mol
  • 19.58\ kcal/mol
  • 40.42\ kcal/mol
  • 20.42\ kcal/mol
A first-order reaction: A\rightarrow B, activation energy is 4.8kcal/mol. When a 20% solution of A was kept at { 27 }^{ o }C for 21.6min, 75% decomposition took place. What will be the percent decomposition in 8.0min in a 30% solution maintained at { 47 }^{ o }C? Assume that activation energy remains constant in this range of temperature.
(e=2.7)
  • 25%
  • 50%
  • 75%
  • 87.5%
Decomposition of a non-volatile solute A into another non-volatile solute B and C, in aqueous solution follows first-order kinetics as:
A\rightarrow 2B+C
When one mole of A is dissolved in 180g water and left for decomposition, the vapour pressure of solution was found to be 20mm Hg after 12h. What is the vapour pressure of solution after 24h?
Assume constant temperature of { 25 }^{ o }C, throughout. The vapour pressure of water at { 25 }^{ o }C is 24mm Hg
  • 18mm Hg
  • 19.2mm Hg
  • 10mm Hg
  • 16mm Hg
What is overall activation energy of reaction, if steps (1) to (4) are much faster than (5)?
  • \cfrac { { E }_{ { a }_{ 5 } }.{ E }_{ { a }_{ 3 } }.{ E }_{ { a }_{ 1 } }^{ 1/2 } }{ { E }_{ { a }_{ 4 } }.{ E }_{ { a }_{ 2 } }^{ 1/2 } }
  • { E }_{ { a }_{ 5 } }+{ E }_{ { a }_{ 3 } }+\cfrac { 1 }{ 2 } { E }_{ { a }_{ 1 } }-{ E }_{ { a }_{ 2 } }- { E }_{ { a }_{ 4 } }
  • { E }_{ { a }_{ 1 } }+{ E }_{ { a }_{ 3 } }+{ E }_{ { a }_{ 5 } }-{ E }_{ { a }_{ 2 } }-{ E }_{ { a }_{ 4 } }\quad
  • -{ E }_{ { a }_{ 5 } }-{ E }_{ { a }_{ 3 } }-\cfrac { 1 }{ 2 } { E }_{ { a }_{ 1 } }+{ E }_{ { a }_{ 2 } }+\cfrac { 1 }{ 2 } { E }_{ { a }_{ 4 } }
Arrhenius equation gives the change in rate constant (and hence rate of reaction) with temperature. If the activation energy of the reaction is found to be equal to RT, then
  • The rate of reaction does not depend upon initial concentration
  • The rate constant becomes about 35% of the Arrhenius constant A
  • The rate constant becomes equal to 73% of the Arrhenius constant A
  • The rate of the reaction becomes infinite or zero
The plot of concentration of a reactant vs time for a chemical reaction is shown below :
The order of this reaction with respect to the reactant is: 
1688350_1392e5391d684ce5a8ec97d877e202e7.png
  • 0
  • 1
  • 2
  • not possible to determine from this plot
Under what condition the order of the reaction,
2HI(g)\rightarrow H_2(g)+I_2(g), is zero.
  • At high temperature
  • At high partial pressure of HI
  • At low partial pressure of HI
  • At high partial pressure of H_2
  • At high partial pressure of I_2
Desorption of a gas from metal surface follows first-order kinetics. The rate constant of desorption can be given by Arrhenius equation. If the desorption of hydrogen on manganese is found to increase 10 times on increasing the temperature from 600 to 1000 K, the activation energy of desorption is :
  • 6.0\ kcal/mol
  • 6.9\ kcal/mol
  • 3.0\ kcal/mol
  • 57.4\ kcal/mol
For a first-order reaction,
  • The degree of dissociation is equal to \left(1-{e}^{-kt}\right)
  • A plot of reciprocal concentration of the reactant vs time gives a straight line
  • The time taken for completion of 75\% reaction is thrice the {t}_{1/2} of the reaction
  • The pre-exponential factor in the Arrhenius equation has the dimension of time, {T}^{-1}
For the combustion of carbon, \quad \Delta H=-ve and \Delta S=+ve  and hence, thermodynamically the process is spontaneous at all temperatures. But coal stored in coal depots does not burn automatically because of
  • very high threshold energy barrier
  • thermodynamically stability of coal
  • lower energy of activation needed for burning
  • low temperature in coal depots
Which of the following curves represents a zero order reaction?
Which of the following curves represents a first order reaction?
The reaction A+B\to C+D;\ \Delta H=25\ kJ/ mole should have an activation energy :
  • -25\ kJ/ mole
  • < 25\ kJ/ mole
  • > 25\ kJ/ mole
  • either answer (B) or (C) depending upon experiment
Which of the following statements is wrong about reactions?
  • There can be only three values of molecularity, that is 1, 2, and 3.
  • There can be only four values of order, that is , 0, 1, 2, and 3.
  • There can be infinite number of values for order.
  • The order involves rate while molecularity does not
50\% of a zero order reaction completes in 10 minutes. 100\% of the same reaction shall complete in: 
  • 5\ min
  • 10\ min
  • 20\ min
  • \infty time
The rate for a first order reaction is 0.6932\times 10^{-2}\ mol\ L^{-1}\ min^{-1} and the initial concentration of the reactant is 0.1\ M. t_{\tfrac{1}{2}} is equal to:
  • 0.6932\times 10^{-2}\ min
  • 0.6932\times 10^{-3}\ min
  • 10\ min
  • 6.932\ min
For a zero order reaction with the initial reactant concentration a, the time for completion of the reaction is
  • k/a
  • a/k
  • 2k/a
  • a/2k
Which of the following curves represent(s) a zero-order reaction ?
In which of the following reactions of the following orders the molecularity and order can never be same?
  • Zero order
  • First order
  • Second order
  • Third order
A plot of reactant concentration versus time for a reaction is a straight line with a negative slope giving the rate constant, and the intercept, giving the initial concentration of the reactant. The order of the reactant is:
  • 0
  • 1
  • 2
  • None of these
For a reaction of the order of 0.5, when the concentration of the reactant is doubled the rate
  • doubles
  • increases four times
  • decrease four times
  • increases \sqrt{2} times
The rate constant of a first-order reaction is 6.93 \times 10^{-2} min^-. The half-life of the reaction is
  • 10 \min
  • 100 \min
  • 1 \min
  • 1000 \min
For a first order reaction A\xrightarrow [  ]{ k } B, the degree of dissociation is equal to
  • e^{-kt}
  • 1-e^{-kt}
  • e^{kt}
  • 1+e^{-kt}
The order w. r. t A is :
1745762_9af02155b13948a885e896e59bd6be57.png
  • 1
  • 2
  • 3
  • -1
The time for the half-life period of a certain reaction A\to products is 1 hour. When the initial concentration of the reactant, A is 2.0\ mol\ L^{-1}. How much time does it take initial concentration to make from 0.50 to 0.25\ mol\ L^{-1} if it is a zero-order reaction?
  • 4\ h
  • 0.5\ h
  • 0.25\ h
  • 1\ h
The number of collisions depend upon
  • Pressure
  • Concentration
  • Temperature
  • All the above
The rate constant is doubled when temperature increases from 27^{o}C to 37^{o}C. Activation energy in kJ is:
  • 34
  • 53.6
  • 100
  • 50
The energy of activation is
  • The energy associated with the activated molecules
  • Threshold energy energy of normal molecules
  • Threshold energy + energy of normal molecules
  • Energy of products energy of reactants
Activation energy is given by the formula
  • \log{\frac{K_2}{K_1}}=\frac{E_a}{2.303R}\left[\frac{{T_2}-{T_1}}{{T_1}{T_2}}\right]
  • \log{\frac{K_1}{K_2}}=-\frac{E_a}{2.303R}\left[\frac{{T_2}-{T_1}}{{T_1}{T_2}}\right]
  • \log{\frac{K_1}{K_2}}=-\frac{E_a}{2.303R}\left[\frac{{T}_{1}-{T_2}}{{T_1}{T_2}}\right]
  • None of these
A graph between t_{1/2}​ and concentration for n^{th}-order reaction is a straight line. The reaction of this nature is completed 50\% in 10 minutes when concentration is 2\  mol. L^{−1}. This is decomposed 50\% in t minutes at 4 mol. L^{−1}. Then n and t are respectively:
1745831_b9c8d61eadcb47cd9ce9be4c8e486621.png
  • 0, 20 min
  • 1, 10 min
  • 1, 20 min
  • 0, 5 min
The energy of activation for reaction (KJ/mol) is :
1745770_53820cf9e14141e18be14ad115b20e2a.png
  • 20.83
  • 13.83
  • 15.23
  • 10.23
8 gm of the radioactive isotope, cesium-137 were collected on February 1 and kept in a sealed tube. On July 1, it was found that only 0.25 gm of it remained. So the half-life period of the isotope is:
  • 37.5 days
  • 30 days
  • 25 days
  • 50 days
For a zero order reaction
  • The concentration of the reactant does not change during the reaction
  • The concentration change only when the temperature changes
  • The rate remains constant throughout
  • The rate of the reaction is proportional to the concentration
Half-life of a radioactive substance which disintegrates by 75\% in 60 minutes, will be
  • 120 min
  • 30 min
  • 45 min
  • 20 min
A zero order reaction is one whose rate is independent of_________________________
  • Temperature of the reaction
  • The concentrations of the reactants
  • The concentration of the products
  • The material of the vessel in which the reaction is carried out
Certain bimolecular reactions which follow the first order kinetics are called_________________________ 
  • First order reactions
  • Unimolecular reactions
  • Bimolecular reactions
  • Pseudounimolecular reactions
Half-life of 10 gm of radioactive substance is 10 days. The half-life of 20 gm is:
  • 10 days
  • 20 days
  • 25 days
  • Infinite
The \Delta H value of the reaction H_2 + Cl_2 \rightleftharpoons 2HCl is -44.12 \,kcal. If E_1 is the activation energy of the products, then for the above reaction
  • E_1 > E_2
  • E_1 < E_2
  • E_1 = E_2
  • \Delta H is not related to E_1 and E_2
  • None is correct
Half-life period of a zero order reaction is:
  • Inversely proportional to the concentration
  • Independent of the concentration
  • Directly proportional to the initial concentration
  • Directly proportional to the final concentration
If 2.0 g of a radioactive isotope has a half-life of 20 hr, the half-life of 0.5 g of the same substance is:
  • 20 hr
  • 80 hr
  • 5 hr
  • 10 hr
A radioactive isotope decays at such a rate that after 96 minutes only \dfrac{1}{8}th of the original amount remains. The half-life of this nuclide in minutes is:
  • 12
  • 24
  • 32
  • 48
Number of \alpha-particles emitted per second by a radioactive element falls to 1/32 of its original value in 50 days. The half-life-period of this elements is:
  • 5 days
  • 15 days
  • 10 days
  • 20 days
The radium and uranium atoms in a sample of uranium mineral are in the ratio of 1:2.8 \times 10^6. If the half-life period of radium is 1620 years, the half-life period of uranium will be:
  • 45.3 \times 10^9 years
  • 45.3 \times 10^{10} years
  • 4.53 \times 10^9 years
  • 4.53 \times 10^{10} years
If the order of the reaction x+y\xrightarrow[]{hv}xy is zero, it means that the rate of ____
  • Reaction is independent of temperature
  • Formation of activated complex is zero
  • Reaction is independent of the concentration of reacting species
  • Decomposition of activated complex is zero
8 \ gms of a radioactive substance is reduced to 0.5 g after 1 hour. The t_{1 / 2} of the radioactive substance is:
  • 15 min
  • 30 min
  • 45 min
  • 10 min
0:0:1


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