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

For the following first-order competing reaction:
$$A+Reagent\rightarrow product$$
$$B+Reagent\rightarrow Product$$
the ratio of $${ K }_{ 1 }/{ K }_{ 2 }$$, if only $$50$$% of $$B$$ will have been reacted when $$94$$% of $$A$$ has been reacted is
$$\left( \log { 2 } =0.3,\log { 3 } 0.48 \right) $$
  • $$4.06$$
  • $$0.246$$
  • $$8.33$$
  • $$0.12$$
In the given first-order sequential reactions:
$$A\xrightarrow [  ]{ { K }_{ 1 } } B\xrightarrow [  ]{ { K }_{ 2 } } C\xrightarrow [  ]{ { K }_{ 3 } } D$$, what is the ratio of number of atoms of $$A$$ to the number of atoms of $$B$$ after long time interval starting with pure $$A$$?
$$\left( { K }_{ 1 }\cfrac { \ln { 2 }  }{ 1200 } ;{ K }_{ 2 }=\cfrac { \ln { 2 }  }{ 30 }  \right) $$
  • $$0.67$$
  • $$10$$
  • $$20$$
  • $$40$$
Two reactions: (I) $$A\rightarrow products$$ and (II) $$B\rightarrow products$$, 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
  • $$0.0233{ min }^{ -1 }$$
  • $$0.0327{ min }^{ -1 }$$
  • $$0.0164{ min }^{ -1 }$$
  • $$0.0654{ min }^{ -1 }$$
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
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