Chemical Kinetics MCQs Class XII

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Section A

The rate of reaction A + B–> Products is given by the equation r = k[ A] [ B] . If B is taken in large excess, the order of reaction would be: a) Cannot be predicted b) 0 c) 2 d) 1

The rate of reaction A + B–>Products is given by the equation r = k[ A] [ B] . If B is taken in large excess, the order of reaction would be: a) Cannot be predicted b) 0 c) 2 d) 1

The slope in the plot of [ R] vs. time for a zero-order reaction is a) – k/2.303 b) k/2.303 c) k/2.303 d) +k

The slope in the plot of ln[ R] vs. time for a first-order reaction is a) -k/2.303 b) -k c)-k/2.303 d) +k

The unit of rate constant depends upon the: a) temperature of the reaction b) molecularity of the reaction c) activation energy of the reaction d) order of the reaction

The half-life for a zero order reaction equals: where R is the initial concentration. a) R^2/2k b) R/2k c) k/2R^2 d) 2k/R

The slope in the plot of [ R] vs. time for a zero-order reaction is a) –  k b)-k/2.303 c) +k/2.303 d) +k

The half-life for a zero-order reaction equals: where [R]0 is the initial concentration. a) 0.693/k b)2.303/k c) 2k/R0 d) R0/2k

A reaction is first order in A and second order in B. How is rate affected when concentration of both A and B are doubled? Choose the correct option: a) two times b) eight times c) four times d) three times

The addition of catalyst during a chemical reaction alters which of the following quantities of the reaction? a) Internal energy b) Activation energy c) Enthalpy d) Entropy

The half - life of a reaction is doubled when the initial concentration is doubled. The order of the reaction is: a) 0 b) 4 c) 1 d) 2

The number of molecules that react with each other in an elementary reaction is a measure of the: a) molecularity of the reaction b) stoichiometry of the reaction c) order of the reaction d) activation energy of the reaction

In the Arrhenius equation, when log k is plotted against , a straight line is obtained whose: a) slope is -Ea/2.303R and intercept is log A. b) slope isA/R and intercept is Ea  . c) slope is A and intercept is -Ea/R d) slope is -Ea/RT and intercept is log A.

The slope in the plot of ln [ R] Vs. time gives (where [ R] is the final concentration of reactant.) a) + k b) c) d) –  k

When a catalyst increases the rate of a chemical reaction, then the rate constant (k): a) may increase or decrease depending on the order of the reaction b) remains constant c) decreases d) increases

The slope of the linein the plot of concentration [ A] Vs. time (s) indicate a) +k b) –  k c) d)

The slope in the plot of log vs. time for a first order reaction is a) –  k b) c) d) +k

A reaction follows second order kinetics. How is the rate of reaction affected if the concentration of the reactant is reduced to half? Choose the correct value from the following: a) four times b)  of the original value c) three times d) eight times

Value of Henry’s constant K : a) increases with decrease in temperature. b) remains constant. c) increases with increase in temperature. d) decreases with increase in temperature.

For a zero order reaction of the type A products, the rate equation may be expressed as: a) b) c) d)

A reaction A + B   2AB occurs by the following mechanism: A   A + A (slow) A + B   AB + B (fast) A + B  AB (fast) Its order would be: a) 1 b) c) Zero d) 2

For a zero order reaction A products,  is: where [ A]  = initial concentration of the reactant, k = rate constant. a) b) c) d)

The rate law for a particular reaction is given as rate = k[ A] [ B] . How is the rate of reaction affected if we double the concentration of B? a) becomes half b) three times c) two times d) four times

For the reaction A + 2B C + D, the rate law is given by r = k[ A] [ B]  , the concentration of A is kept constant while that of B is doubled. The rate of the reaction will: a) not change b) become half c) quadruple d) double

Half –  life period of a first order reaction is 1386 seconds. The rate constant (k) of the reaction is: a) 0.5 10  s b) 5.0 10  s c) 0.5 10  s d) 5 10  s

The order of the reaction is: a) 3 b) 1 c) 0 d) 2

For the reaction 3A 2B, rate of reaction  is equal to a) b) c) d)

For the reaction 3A 2B, rate of reaction  is equal to a) b) c) d)

For a certain reaction R products, a plot of log [ R] vs. time gives a straight line with a slope of 1.25 s  . The order of the reaction is: a) One b) Zero c) Two d) Fractional

A first order reaction takes 30 minutes for 50% completion. The value of rate constant k would be: a) 2.31 10  min b) 1.25 10  min c) 2.75 10  min d) 2.5 10  min

If the initial concentration is reduced to  in a zero order reaction, then the time taken for half the reaction to complete: a) remains the same b) doubles c) increases four times d) reduces to one –  fourth

For a reaction 2A–> 3B, rate of reaction is equal to a) b) c) d)

In a chemical reaction X Y, it is found that the rate of reaction doubles when the concentration of X is increased four times. The order of the reaction with respect to X is a) b) 2 c) 1 d) 0

For a zero order reaction, the slope in the plot of [ R] vs. time is (where, [ R] is the final concentration of reactant) a) –  k b) c) +k d)

For the elementary reaction P Q, the rate of disappearance of ’P’ increases by a factor of 8 upon doubling the concentration of ’P’. The order of the reaction with respect to ’P’ is: a) 1 b) 2 c) 4 d) 3

The unit of the rate of reaction is the same as that of the rate constant for a: a) it cannot be same b) first order reaction c) zero order reaction d) second order reaction

The rate constant for a first order reaction is equal to the initial rate ofreaction when the initial concentration of the reactant is a) 0.1 M b) 10 M c) 1 M d) 1 10  M

A zero –  order reaction is one whose rate is independent of: a) Presence of light b) Pressure of the reaction c) Concentration of the reactant d) Temperature of the reaction

The rate of the reaction 2A + B  2AB is given by Rate = k[ A]  [ B  ] . The value of rate constant (k) can be increased by: a) All of these b) increasing the concentration of A c) increasing the concentration of B d) increasing the temperature

Unit of rate constant for the zero order reaction is: a) mol L  s b) mol L s c) s d) mol L s

Class 12 Solution Chapter Important Questions

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Chemical Kinetics Assertion and Reason Questions

Assertion (A) & Reason ( R )

a) Both A and R are true and R is the correct explanation of A.

b) Both A and R are true but R is not the correct explanation of A.

c) A is true but R is false.

d) A is false but R is true.

Assertion (A): Rate of reaction can be expressed as rate of change in partial pressure of the reactant or product. Reason (R): Partial pressure of a gas is equal to its concentration.

Assertion (A): The order of a reaction may be negative. Reason (R): In some cases, the rate of reaction decreases as the concentration of the reactant increases.

Assertion (A): Elementary reactions have same value of order and molecularity. Reason (R): Molecularity is the number of molecules that participate in the reaction, while order is an experimental quantity.

Assertion (A): The overall order of the reaction is the sum of the exponents of all the reactants in the rate expression. Reason (R): There are many higher order reactions.

Assertion (A): For the reaction: RCI + NaOH (aq)  ROH + NaCI, the rate of reaction is reduced to half when the concentration of RCI is reduced to half. Reason (R): The rate of reaction is represented by k[ RCI] i.e., it is a first order reaction.

Assertion (A): The molecularity of the reaction H  + Br   2HBr is 2. Reason (R): Order of the reaction 3/2.

Assertion (A): The molecularity of the reaction is H  + Br  = 2HBr is two. Reason (R): The order of this reaction is  .

Assertion (A): For complex reactions molecularity and order are not same. Reason (R): Order of reaction may be zero.

Assertion (A): For a zero order reaction the unit of rate constant and rate of reaction are same. Reason (R): Rate of reaction for zero order reaction is independent of concentration of reactant.

Assertion (A): Order of the reaction can be zero or fractional. Reason (R): We cannot determine order from balanced chemical equation.

Assertion (A): The photochemical reactions H  + Cl   2HCland H  + Br   2HBrhave equal quantum efficiencies. Reason (R): Both the reactions proceed by similar mechanism.

Assertion (A): For the first –  order reaction the units of the rate constant are time  . Reason (R): The rate of the first –  order reaction remains constant throughout.

Assertion (A): Order and molecularity are the same. Reason (R): Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of the rate –  determining elementary step.

Assertion (A): Reactions of higher order are rare. Reason (R): The chances of simultaneous multimolecular collisions are extremely small.

Assertion (A): Hydrolysis of an ester follows first –  order kinetics. Reason (R): Concentration of water remains nearly constant during the course of the reaction.

Assertion (A): p –  nitroaniline is a weaker base than p –  toluidine. Reason (R): The electron donating –  NO  group in p –  nitroaniline makes it a weaker base.

Assertion (A): Order of reaction is applicable to elementary as well as complex reactions. Reason (R): For a complex reaction molecularity has no meaning.

Assertion (A): The molecularity of the reaction H  + Br   2HBr appears to be 2. Reason (R): Two molecules of the reactants are involved in the given elementary reaction.

Assertion (A): If the activation energy of a reaction is zero, temperature will have no effect on the rate constant. Reason (R): Lower the activation energy, faster is the reaction.

Assertion (A):

Assertion (A): The rate of the reaction is the rate of change of concentration of a reactant or a product. Reason (R): Rate of reaction remains constant during the complete reaction.

Assertion (A): Order of reaction and molecularity are always same for complex reactions. Reason (R): Order is determined experimentally and molecularity is applicable only for elementary reactions.

Assertion (A): Order and molecularity of a reaction are always same. Reason (R): Complex reactions involve a sequence of elementary reactions and the slowest step is rate determining.

Assertion (A): The presence of a catalyst increases the speed of the forward and backward reaction to the same extent. Reason (R): Activation energy for both the forward and the backward reactionsis lowered to the same extent.

Assertion (A): If in a zero order reaction, the concentration of the reactant is doubled, the half –  life period is also doubled. Reason (R): For a zero order reaction, the rate of reaction is independent of initial concentration.

Assertion (A): The enthalpy of reaction remains constant in the presence of a catalyst. Reason (R): A catalyst participating in the reaction, forms a different activated complex and lowers down the activation energy but the difference in energy of reactant and product remains the same.

Assertion (A): For complex reactions, molecularity and order are same. Reason (R): Order of a reaction may be zero.

Assertion (A): The reaction  and   , proceed at the same rate because they are similiar Reason (R): Both the reactions have the same activation energy.

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