CBSE Class 12 Chemistry Chemical Kinetics Worksheet

State whether given statement is true or false.

1. The unit of K for first order reaction is molL^-1s^-1. ( )

2. The radioactive decay follows zero order kinetics. ( )

3. For r =k[A]²[B],the order of reaction is 3 ( )

4. For second order reaction unit of k is mol^-2L2s^-1. ( )

5. For a reaction order and molecularity are always same. ( )

6. Order of reaction is always a whole number whereas molecularity can be fractional. ( )

MCQ

1.The order of reaction for,r=k[A]²[B] is

(a). 1 b) 0 (c)2 (d) 3

2.A reaction 50% complete in 2 hours and 75% in 4 hours, the order of reaction will be

(a).0 b) 1 (c)2 (d) 3

3.For a reaction A+B → C,the rate law is given by r=k[A]^1/2[B]² the order of reaction is:

(a).0 b) 5/2 (c)2 (d) 3/2

4. What is the unit of K if rate ==K{A}2{B}

(a) s^-1 (b) mol L^-1 (c) mol^-2L²s^-1 (d) mol^-1Ls^-1

5.What is the molecularity of reaction for the following elementary reaction:

2A+B------------------------→C

(a) 1 (b) 2 (c) 3 (d) 0

6.What is the order for following photochemical reaction:

H₂+Cl₂------------→2HCl 
 

Important Questions for NCERT Class 12 Chemistry Chemical Kinetics

Question. For the reaction; 2N₂O₅ → 4NO₂ + O₂ rate and rate constant are 1.02 × 10^–4 and 3.4 × 10^–5 sec–1 respectively, then concentration of N₂O₅ at that time will be
(a) 1.732
(b) 3
(c) 1.02 × 10^–4
(d) 3.4 × 10⁵

Question. The given reaction,
2FeCl₃ + SnCl₂ → 2FeCl₂ + SnCl₄ is an example of
(a) third order reaction
(b) first order reaction
(c) second order reaction
(d) none of these.

Question. The rate constant for a first order reaction is 4.606 × 10^–3 s^–1. The time required to reduce 2.0 g of the reactant to 0.2 g is
(a) 100 s
(b) 200 s
(c) 500 s
(d) 1000 s 

Question. If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by
(a) t = 2.303/k
(b) t = 0.693/k
(c) t = 6.909/k
(d) t = 4.606/k

Question. A first order reaction has a rate constant of 2.303 × 10^–3 s^–1. The time required for 40 g of this reactant to reduce to 10 g will be [Given that log₁₀ 2 = 0.3010]
(a) 230.3 s
(b) 301 s
(c) 2000 s
(d) 602 s

Question. The correct difference between first and second order reactions is that
(a) the rate of a first-order reaction does not depend on reactant concentrations; the rate of a second-order reaction does depend on reactant concentrations
(b) the half-life of a first-order reaction does not depend on [A]0 ; the half-life of a second-order reaction does depend on [A]0
(c) a first-order reaction can be catalysed; a secondorder reaction cannot be catalysed
(d) the rate of a first-order reaction does depend on reactant concentrations; the rate of a secondorder reaction does not depend on reactant concentrations. 

Question. When initial concentration of the reactant is doubled, the half-life period of a zero order reaction
(a) is halved
(b) is doubled
(c) is tripled
(d) remains unchanged.

Question. A first order reaction has a specific reaction rate of 10^–2 sec^–1. How much time will it take for 20 g of the reactant to reduce to 5 g?
(a) 138.6 sec
(b) 346.5 sec
(c) 693.0 sec
(d) 238.6 sec 

Question. The rate of first-order reaction is 0.04 mol L^–1 s^–1 at 10 seconds and 0.03 mol L–1 s^–1 at 20 seconds after initiation of the reaction. The half-life period of the reaction is
(a) 44.1 s
(b) 54.1 s
(c) 24.1 s
(d) 34.1 s

Question. When initial concentration of a reactant is doubled in a reaction, its half-life period is not affected. The order of the reaction is
(a) second
(b) more than zero but less than first
(c) zero
(d) first. 

Question. The decomposition of phosphine (PH₃) on tungsten at low pressure is a first-order reaction. It is because the
(a) rate is proportional to the surface coverage
(b) rate is inversely proportional to the surface coverage
(c) rate is independent of the surface coverage
(d) rate of decomposition is very slow.
Answer   A

Question. The rate constant of the reaction A B is 0.6 × 10^–3 mol L–1 s^–1. If the concentration of A is 5 M, then concentration of B after 20 minutes is
(a) 3.60 M
(b) 0.36 M
(c) 0.72 M
(d) 1.08 M 
Answer   C

Question. For a reaction between A and B the order with respect to A is 2 and the order with respect to B is 3.
The concentrations of both A and B are doubled, the rate will increase by a factor of
(a) 12
(b) 16
(c) 32
(d) 10
Answer   C

Question. In a reaction, A + B → product, rate is doubled when the concentration of B is doubled, and rate increases by a factor of 8 when the concentration of both the reactants (A and B) are doubled, rate law for the reaction can be written as
(a) rate = k[A][B]²
(b) rate = k[A]²[B]²
(c) rate = k[A][B]
(d) rate = k[A]²[B]
Answer   D

Question. Which one of the following statements for the order of a reaction is incorrect?
(a) Order can be determined only experimentally.
(b) Order is not influenced by stoichiometric coefficient of the reactants.
(c) Order of a reaction is sum of power to the concentration terms of reactants to express the rate of reaction.
(d) Order of reaction is always whole number.
Answer   D

Question. The unit of rate constant for a zero order reaction is
(a) mol L^–1 s^–1
(b) L mol^–1 s^–1
(c) L2 mol^–2 s^–1
(d) s^–1
Answer   A

Question. For the reaction, A + B → products, it is observed that
(i) on doubling the initial concentration of A only, the rate of reaction is also doubled and
(ii) on doubling the initial concentration of both A and B, there is a change by a factor of 8 in the rate of the reaction.
The rate of this reaction is given by
(a) rate = k[A][B]²
(b) rate = k[A]²[B]²
(c) rate = k[A][B]
(d) rate = k[A]²[B]
Answer   A

Question. The rate of reaction between two reactants A and B decreases by a factor of 4 if the concentration of reactant B is doubled. The order of this reaction with respect to reactant B is
(a) 2
(b) –2
(c) 1
(d) –1
Answer   B

Question. If the rate of the reaction is equal to the rate constant, the order of the reaction is
(a) 0
(b) 1
(c) 2
(d) 3 
Answer  A

Question. 2A B → C, It would be a zero order reaction when
(a) the rate of reaction is proportional to square of concentration of A
(b) the rate of reaction remains same at any concentration of A
(c) the rate remains unchanged at any concentration of B and C
(d) the rate of reaction doubles if concentration of B is increased to double.
Answer   B

ASSERTION-REASON TYPE QUESTIONS

A statement of assertion is followed by a statement of a reason. Mark the correct choice from the options given below:
a) Both assertion and reason are true and reason is the correct explanation of assertion.
b) Both assertion and reason are true but reason is not the correct explanation of assertion.
c) Assertion is true but reason is false.
d) Assertion is false and reason is true

Question. Assertion: Rate constant of a zero-order reaction has same units as the rate of reaction.
Reason: Rate constant of a zero-order reaction does not depend upon the concentration of reactant.
Answer. C

Question. Assertion : The molecularity of the reaction , H₂ + Br₂ → 2 HBr is 2
Reason : The order of the reaction can be determined only experimentally.
Answer. B

Question. Assertion: All collision of reactant molecules lead to product formation.
Reason: Only those collisions in which molecules have correct orientation and sufficient kinetic energy lead to compound formation
Answer. D

Question. Assertion : Half-life period is always independent of initial concentration .
Reason : Half-life Period is inversely proportional to rate constant.
Answer. C

Question. Assertion: Diamond shall convert to graphite.
Reason: The rate is so slow that the change is not perceptible at all.
Answer. A

Question. Assertion: A catalyst does not alter the free energy change of a reaction.
Reason: A catalyst lowers the activation energy of a process.
Answer. B

Question. Assertion: According to collision theory the rate of reaction does not depend on collision frequency.
Reason: The collisions in which molecules collide with sufficient kinetic energy and proper orientation are called effective collisions.
Answer. D

Question. Assertion: The slowest elementary step in a complex reaction decides the rate of the reaction.
Reason: The slowest elementary step always has the smallest molecularity.
Answer. C

Question. Assertion: Hydrolysis of methyl ethanoate is a pseudo first order reaction.
Reason: Water is present in large excess and therefore its concentration remained Constant throughout the reaction.
Answer. A

Question. Assertion: The order for a reaction with rate constant k=3x104s^-1 is 1.
Reason: Order of a reaction is the sum of the powers to which concentration terms are raised to in the rate law
Answer. B

Question. Assertion : Rate constant of a zero order reaction has the same units as the rate of reaction .
Reason : Rate of a zero order reaction does not depend on the concentration.
Answer. B

Question. Assertion: 50% of a reaction is completed in 50 sec, 75% of the reaction will be completed in 75 sec.
Reason: The rate constant of a zero-order reaction depends upon time.
Answer. C

Question. Assertion: The thermal decomposition of HI on gold is a zero-order reaction.
Reason: The thermal decomposition of HI on gold depends on the initial concentration
Answer. C

Question. Assertion: The reaction X→Y follows second order kinetics. If concentration of X increased 3 times rate become 3 times.
Reason: The rate of a reaction is directly proportional to the concentration of reactants
Answer. D

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

SHORT ANSWER QUESTIONS

Question. Define rate of a reaction? What is the SI Unit of rate of reaction? 
Answer. Change in molar concentration of reactant or product in per unit time is called rate of reaction. Unit of rate: MolL^-1S^-1

Question. (i) State rate law? 
(ii) For a reaction in 10 minutes concentration of reactant reduced from 0.12μg to 0.06 μg and in next 10 minutes it becomes 0.03 μg. find the order of this reaction.
Answer. (i) Expression in which reaction rate is given in terms of molar conc. of reactants with each term rise to some power which may or may not be same as the stoichiometric coefficient of the reacting species in a balanced chemical equation.
(ii) Since in every 10 minutes concentration becomes half. Half-life is independent of concentration for first order reaction. So it is a first order reaction

Question. The kinetic of the reaction 2NO + 2H₂ → N₂ + 2H₂O is explained by the following steps: 
(i) 2NO + H₂ → N₂ + H₂O₂ …… slow
(ii) H₂O₂ + H₂ → 2H₂O ……… fast
What is the rate law for the reaction?
Answer. Slow reaction is the rate determining step.
Rate law, rate = k[NO]²[H₂]

Question. For a reaction A + B → P, the rate is given by Rate = k[A] [B]²
a. How is the rate of reaction affected if the concentration of B is doubled?
b. What is the overall order of reaction if A is present in large excess?
Answer. a) Rate will increase 4 times of the actual rate of reaction
b) 2nd order

Question. A) What are complex reactions?
B) What is the order of reaction whose unit of rate constant and rate of reaction are same?
Answer. i) Reactions taking place in more than one step are called complex reaction.
ii) Zero order

Question. When ammonia and oxygen react at high temperature nitrogen (II) oxide and water are formed. In an experiment the rate of formation of NO was found to be 3.2x10^-3molL-1s^-1.Compute the rate of disappearance of ammonia and rate of formation of water. The reaction is 4NH₃ + 5O₂ → 4NO + 6 H₂O 
Answer. For the given reaction general rate is
Rate = -Δ [NH₃]/4Δt = -Δ [O₂]/5 Δt = Δ [NO]/4Δt = Δ [H₂O]/6Δt
Rate of disappearance of ammonia = Rate of formation of NO = 3.2x10^-3molL^-1s^-1
Rate of formation of water = 6/4 * Rate of formation of NO = 6x3.2x10^-3/4 = 4.8x10^-3molL^-1s^-1

Question. i) Identify the reaction order from the rate constant k=2.3x10^-5 mol-1 Ls^-1 
ii) Define molecularity of a reaction.
Answer. i) 2
ii) The number of reacting species taking part in an elementary reaction which must colloid simultaneously in order to bring about a chemical reaction is called molecularity of reaction.

Question. Define the following : (i) Elementary step in a reaction (ii) Rate of a reaction 
Answer. (i) Elementary step in a reaction: Those reactions which take place in one step are called elementary reactions. Example : Reaction between H₂, and I₂ to form 2HI H₂ + I₂ → 2HI (ii) Rate of a reaction: The change in the concentration of any one of the reactants or products per unit time is called rate of reaction.

Question. Define the following : (i) Order of a reaction (ii) Activation energy of a reaction 
Answer. (i) Order of a reaction : It is the sum of powers of molar concentrations of reacting species in the rate equation of the reaction. It may be a whole number, zero, fractional, positive or negative. (ii) Activation energy of a reaction: The minimum extra amount of energy absorbed by the reactant molecules to form the activated complex is called activation energy.

Question. A reaction is of first order in reactant A and of second order in reactant B. How is the rate of this reaction affected when (i) the concentration of B alone is increased to three times (ii) the concentrations of A as well as B are doubled? 
Answer. r = K[A]¹ [B]²
(i) When concentration of B increases to 3 times, the rate of reaction becomes 9 times
r = KA(3B)² ∴ r = 9KAB² = 9 times
(ii) r = K(2A) (2B)² ∴ r = 8KAB² = 8 times

Question. Distinguish between ‘rate expression’ and ‘rate constant’ of a reaction. 
Answer. Rate expression: The expression which expresses the rate of reaction in terms of molar concentrations of the reactants with each term raised to their power, which may or may not be same as the stoichiometric coefficient of that reactant in the balanced chemical equation. Rate constant: The rate of reaction when the molar concentration of each reactant is taken as unity.

Question. What do you understand by the rate law and rate constant of a reaction? Identify the order of a reaction if the units of its rate constant are : (i) L^-1 mol s^-1 (ii) L mol^-1 s^-1
Answer. The rate of reaction is found to depend on α concentration of term of reactant A and β concentration term of reactant B Then Rate of reaction ∝ [A]α [B]β or Rate = K [A]α [B]β This expression is called Rate law. ‘K’ in this expression is called Rate constant. Rate constant’s unit : (i) Unit = L^-1 mol s^-1 → Zero order reaction (ii) Unit = L mol^-1 s^-1 → Second order reaction.

Question. A reaction is of second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is reduced to half? What is the unit of rate constant for such a reaction? 
Answer. Rate = K [A]² = Ka²
If [A] = 1/2a Rate = K (1/2a)²=1/4 Ka²
∴ Rate = 1/4^th (one fourth of original rate)
The unit of rate constant is L mol^-1 s^-1

Question. What do you understand by the ‘order of a reaction’? Identify the reaction order from each of the following units of reaction rate constant: (i) L^-1 mol s^-1 (ii) L mol^-1 s^-1 
Answer. Order of reaction: The sum of powers of the concentration of the reactants in the rate law expression is called the order of that chemical reaction.
r = K[A]x[B]y Order = x + y
(i) Zero order
(ii) Second order

Question. Define the following terms :
(a) Pseudo first order reaction.
(b) Half life period of reaction (t_1/2).
Answer.
(a) Those reactions which are not truly of the first order but under certain conditions become first order reactions are called pseudo first order reaction.
(b) The time taken for half of the reaction to complete is called half-life period.

Question. (i) What is the order of the reaction whose rate constant has same units as the rate of reaction?
(ii) For a reaction A + H₂O → B; Rate ∝ [A], What is the order of this reaction?
Answer. (i) The reaction whose rate constant has same units as the rate of reaction, will have zero order of reaction. (ii) The reaction A + H₂O → B Rate ∝ [A] The order of this reaction will be pseudo first order reaction as the rate of reaction depends only on concentration of A only.

Question. What is the effect of adding a catalyst on:(a) Activation energy (Ea) and (b) Gibbs energy (ΔG) of a reaction?
Answer. (a) Catalyst provides a new reaction pathway in which a lower activation is offered. Hence, catalyst increases the rate of reaction by lowering the activation energy. 
(b) Gibbs free energy will remain same as for catalyzed & uncatalyzed reaction, as the equilibrium constant is not affected which is a function of Gibbs free energy.

Question. The decomposition of NH₃ on platinum surface is zero order reaction.If rate constant (k)is 4 x 10^-3 Ms^-1,how long will it take to reduce the initial concentration of NH₃ from 0.1 M to 0.064 M?
Answer. For a zero order reaction,
K=1/t ([A]₀-[A])
t=1 x (0.1-0.064)/4 x 10^-3
=9 s

Question. For a reaction 2H₂O₂ →  2H₂O+O₂ the proposed mechanism is as given below:
(i) H₂O₂ +I-  → H₂O +IO-(slow)
(ii) H₂O₂+IO^- → H₂O +I^- +O₂(fast)
(A)Write rate law for the reaction
(B)Write the overall order of reaction
(c) Out of steps(1) and (2),which one is the rate determining step? 
Answer.
(A)Rate=k[H₂O][I^-]
(B) Overall order of reaction is 2
(c)Step (1) being the slow step is the rate determining step of the reaction.

Question. Define rate of reaction. Write two factors that affect the rate of reaction.
Answer. Rate of reaction : Rate of chemical reaction is equal to change in concentration of reactant or product in unit time.
Two factors :
(1) Concentration of reactants
(2) Temperature of reactants

ONE MARK QUESTIONS

1. Why does the rate of a reaction not remain constant throughout the reaction process? 
2. The rate of a reaction is 1.2 x 10-3 L/mol/s. What is the order of the reaction?

TWO MARK QUESTIONS

1.Define the following terms :
a) Half-life of a reaction (t½)
b) Rate constant (k)

2.A first order decomposition reaction takes 40 minutes for 30% decomposition. Calculate its t1/2 value. 
3.Show that for a first order reaction, the time required for half the change is independent of initial concentration. 

THREE MARK QUESTIONS

1.A reaction is first order in A and second order in B.
a) Write differential rate equation.
b) How is the rate affected when the concentration of A is tripled?
c) How is the rate affected when the concentration of both A and B are doubled?
2.For a certain chemical reaction, variation in the concentration, ln[R] Vs time(s) plot is given below: ln[R] T(s) For the reaction

a) What is the order of the reaction?
b) Give the relationship between k and t1/2
c) What does the slope of the above line indicate? 

(1 MARK QUESTIONS)

1. What do you understand by the rate determining step of a reaction?
Answer : The slowest step in a reaction is known as rate determining step.

2. Find the molecularity of following reaction. RCOOR’ + H₂O → H+→ RCOOH + R’OH
Answer : Molecularity of reaction = 2 (there are two reactant molecules in balanced equation)

3. The rate constant of a reaction is 5.0 X 10^-5 L mol^-1 min^-1. What is the order of the reaction?
Answer : The order of reaction is 2.

4. Why rate of the reaction does not remain constant throughout?
Answer : Rate of reaction depends upon concentration of reactants which keep on decreasing with time.
Hence, rate of reaction does not remain constant throughout.

5. What is the order of reaction whose rate constant has the same units as the rate of reaction?
Answer : Zero order.

6. Write Arrhenius equation.
Answer : Ae-Ea/RT Where,k = Rate constant Ea = Activation energy A = Arrhenius factor

7. Define rate constant or specific reaction rate.
Answer : When the molar concentration of each reactant is unity, the rate of reaction is called specific reaction rate.

8. The reaction A + 3B → 2C obeys the rate equation.Rate = k [A]^1/2 [B]^3/2.
Answer : What is the order of this reaction?
Order =(1/2) + (3/2) = 2

9. What are the units of rate constant for a first order reaction?
Answer : s-1

10. Give one example of a reaction where order and molecularity are equal.
Answer : For elementary reaction, order and molecularity are same. These reactions are carried out only in one step . 2HI → H₂ + I₂.

11. What do you understand by half-life period of a reaction?
Answer : The time taken for half of the reaction to complete is known as half–life period of that reaction.

12. Hydrolysis of ethyl acetate withNaOH is a reaction of second order while with HCl, it is of firstorder. Why?
Answer : Rate of hydrolysis of ethyl acetate with NaOH depends upon concentration of both CH₃COOC₂H₅ and NaOH while with HCl it depends only upon the concentration of ethyl acetate.

13. What is the effect of adding catalyst on the free energy (ΔG) change of a reaction?
Answer : Free energy of the reactants and products remains the same. Hence, there is no change in Δ G on adding catalyst.

14. The rate of a reaction whose rate law is Rate = k [B]nbecomesdouble on doubling the concentration of B. Find the value n.
Answer : n = 1

15. A reaction is 50% complete in 2 hrs. And 75% complete in 4 hrs. What is the order of reaction?
Answer : First order

16. How does catalyst affect rate of reaction?
Answer : A catalyst can increase rate of reaction by lowering down the activation energy. It gives alternate path to the reaction

17. Define threshold energy.
Answer : Threshold energy is minimum energy which the colliding molecules must possess so that the collision between them may be effective.
Threshold energy = Activation energy + energy possessed by reactant molecules.

18. The reaction A+B →  C has zero order. What is the rate equation?
Answer : Rate =k [A]^o [B]^o

19. Which reactions proceed with constant rate?.
Answer : Zero order reactions

2 MARKS QUESTIONS

1. What is (i) Rate law expression? (ii) Rate determining step?

2. (i) This reaction is of first order and rate constant of reaction is 5.7 X 10^-3 S^-1. Find the value of t^1/2.

3. Define (i) Activation energy (ii) Collision freq

4. For a reaction A → B, the rate of reaction doubles when concentration of A is increased by 4. What is the order of reaction?

5. Time required to decompose SO₂Cl₂ to half of its initial amount is 1 hour. If the decomposition is a first order reaction, calculate the rate constant of the reaction.

6. The conversion of molecules from A to B follows second order kinetics. If the concentration of A is increased to five times, how will it affect the rate of formation of B?

7. The rate of decomposition of N₂O₅ is 2.4 x 10^-4mol L-1s-1 when [N₂O₅] is 0.36 M. What is the rate law and value of k for this first order reaction?

8. In a first order reaction, 75% of reactants disappeared in 1.386 hrs. Calculate the rate constant of the reaction.

9. Rate of formation of product for second order reaction is 9.5 x 10^-5mol L-1 s^-1.
The initial concentration of reactant was found to be 0.01 mol/L.
a) Write rate law for second order reaction.
b) Calculate the rate constant for the given second order reaction. 

10. What do you understand by effective collision? What are the factors affecting the effectivecollision?

THREE MARKS QUESTIONS

1. (i) Define half life period.
(ii) The half-life period of reaction is 10 minutes. How long it will take for concentration of reactant to be reduced to 10% of original?

2. Explain the term Activation energy and threshold energy? How temperature affects the rate of reaction?

3. What do you understand by integrated rate equation? Deduce the integrated rate equation for first order reaction?

4.A chemical reaction is of second order w.r.t. a reactant. How will the rate of reaction be affected if the concentration of this reactants : (a) Doubled; (b) Reduced to 1/8th.

5.From the following data for a chemical reaction between A and B at 300 K

Calculate (i) the order of reaction with respect to A and with respect to B.(ii) the rate constant 300K

6. (i) Distinguish between elementary and complex reaction?
(ii) What are the factors affecting the rate of chemical reaction?

7.The decomposition of phosphine₄PH₃(g) → P4(g) + 6H₂(g) has rate law;
Rate = k [PH₃]. The rate constant is 6.0 × 10^–4 s^–1 at 300K and activation energy is 3.05 × 10⁵ J mol^–1. Calculate the value of the rate constant at 310K. (R = 8.314 J k^–1mol^–1).

8.The decomposition of hydrocarbon follows the equation k = (4.5 × 10¹¹ s^–1)e^–28000 K/T. Calculate Ea .

9. Show that for a first order reaction, time required for 99% completion is twice for the time required for the completion of 90% of reaction.

10. The rate of reaction triples when the temperature changes from 20°C to 50°C.
Calculate the energy of activation. [R = 8.314 J k^–1mol^–1, log 3 =0.48]

5 MARKS QUESTIONS

1. (a) For a reaction A + B → Products, the rate law is given by r = k [A]^1/2 [B]² What is the order of reaction?
(b) 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?
(c) Write two points of difference between order and molecularity of a reaction.

2. a) Define (i) Activation energy (ii) Collision frequency
b) The rate constants of a reaction at 500k& 700k are 0.02s^-1& 0.07s^-1 respectively. Calculate thevalue of Ea& A.

3. (i) A reaction is first order in A & second order in B.
a) Write differential rate equation.
b) How is the rate affected on increasing the concentration of B three times?
c) How is the rate affected when conc of both A&B is doubled?
(ii) Name the factors which affect the rate of reaction.

4. a) Deduce the expression of half-life for zero order reaction.
b) Show that time required for 99.9% completion of the first order reaction is 10 times of t1/2 for first order chemical reaction.

5. a) For a reaction A + B Products, the rate law is given by
r = k [A]^1/2 [B]². What is the order of reaction?
(b) T he 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?

Important Questions for NCERT Class 12 Chemistry Chemical Kinetics

Question. A reaction is 50% complete in 2 hours and 75% complete in 4 hours. The order of reaction is
(a) 1
(b) 2
(c) 3
(d) 0

Question. The half-life of a substance in a certain enzymecatalysed reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg L^–1 to 0.04 mg L^–1 is
(a) 414 s
(b) 552 s
(c) 690 s
(d) 276 s 

Question. Half-life period of a first order reaction is 1386 seconds. The specific rate constant of the reaction is
(a) 0.5 × 10–2 s^–1
(b) 0.5 × 10–3 s^–1
(c) 5.0 × 10–2 s^–1
(d) 5.0 × 10–3 s^–1 

Question. If 60% of a first order reaction was completed in 60 minutes, 50% of the same reaction would be completed in approximately (log 4 = 0.60,log 5 = 0.69)
(a) 45 minutes
(b) 60 minutes
(c) 40 minutes
(d) 50 minutes.

Question. For a first order reaction A B the reaction rate at reactant concentration of 0.01 M is found to be 2.0 × 10^–5 mol L–1 s^–1. The half-life period of the reaction is
(a) 30 s
(b) 220 s
(c) 300 s
(d) 347 s 

Question. The rate of a first order reaction is 1.5 × 10^–2 mol L^–1 min^–1 at 0.5 M concentration of the reactant. The half-life of the reaction is
(a) 0.383 min
(b) 23.1 min
(c) 8.73 min
(d) 7.53 min

Question. The reaction A B follows first order kinetics. The time taken for 0.8 mole of A to produce 0.6 mole of B is 1 hour. What is the time taken for conversion of 0.9 mole of A to produce 0.675 mole of B ?
(a) 1 hour
(b) 0.5 hour
(c) 0.25 hour
(d) 2 hours

Question. For a first-order reaction, the half-life period is independent of
(a) first power of final concentration
(b) cube root of initial concentration
(c) initial concentration
(d) square root of final concentration.

Question. For a reaction, activation energy Ea = 0 and the rate constant at 200 K is 1.6 × 10⁶ s^–1. The rate constant at 400 K will be [Given that gas constant R = 8.314 J K^–1 mol^–1]
(a) 3.2 × 104 s^–1
(b) 1.6 × 106 s^–1
(c) 1.6 × 103 s^–1
(d) 3.2 × 106 s^–1

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

Question. For a chemical reaction represented by R → P the rate of reaction is denoted by –d [R]/dt or +d[P]/dt . State the significance of plus and minus sign.
Answer :(–) sign represents decrease in concentration with time while (+) sign represetns increase in concentration.

Question. Express the rate of reaction in terms of disappearance of hydrogen and appearance of ammonia in the given reaction.
Answer :N₂(g) + 3 H₂ (g) → 2NH₃ (g)
Rate= -1/3d[H₂]/dt rate=+1/2d[NH₃]/dt

Question. Why rate of reaction does not remain constant throughout?
Answer :It is because concentration of reactants goes on decreasing with time.

4. Write the unit of first order rate constant of a gaseous reaction if thepartial pressure of gaseous reactant is given in bar.
Answer :s^-1

Question. What will be the order of reaction, if the rate of reaction does not depend on the concentration of any of the reactant.
Answer :zero order

Question. For the elementary step of a chemical reaction : H₂ + I₂ →2HI rate of reaction →[H₂] [I₂] What is the (i) molecularity and (ii) order of the reaction.
Answer :i) 2 ii) 1

Question. For a chemical reaction A→ B. The rate of the reaction is given as Rate = k [A]ⁿ the rate of the above reaction quadruples when the concentration  of A is doubled. What is the value of n?
Answer :n=2

Question. Mention one example of zero order reaction.
Answer :2NH₃ (g)→N₂ (g) +3H₂(g) (at1130K and Pt as catalyst)

Question. What is the value of the order of reaction of radioactive decay?
Answer :First order

Question. Express the relation between the half life period of a reactant and initial concentration for a reaction of nth order.
Answer :t_1/2 α 1/[R]0^n-1 where n is order of reaction.

Question. A reaction is 50% complete in 2 hours and 75% complete in 4 hours. What is the order of reaction?
Answer :First order

Question. Suggest an appropriate reason for the observation : “On increasing temperature of the reacting system by 10 degrees, the rate of reaction almost doubles or even sometimes becomes five folds.”
Answer :Increasing the temperature of the substance increases the fraction of molecules which collide with energy greater than E_a.

Question. For a chemical reaction, activation energy is zero and at 300K rate constant is 5.9 × 10^-5s^–1, what will be the rate constant at 400K?
Answer :5.9 × 10^–5 s^–1

Question. Two reactions occuring at the same temperature have identical values of Ea. Does this ensure that also they will have the same rate constant? Explain.
Answer :No,because the Rate depends on the nature and concentrations of reactants and also pre-exponential factor.

Question. The rate constant of a reaction is given by the expression k = Ae–Ea/RT Which factor in this expression should register a decrease so that the reaction proceeds rapidly?
Answer :E_a should. Deacrease. : Rate = k [AB₂] [C₂]; Order = 1 + 1 = 2]

Question. For a chemical reaction rate constant k = 5.3 × 10^-4mol L–1 s^–1, what will be the order of reaction?
Answer :zero order reaction

Question. Write the rate law and order for the following reaction :
Answer :AB₂ + C2→AB₂C + C (slow)
AB₂ + C→AB₂C (Fast)]
Rate = k [AB₂] [C₂]; Order = 1 + 1 = 2]

Question. The conversion of molecules X to Y follows second order kinetics.If concentration of Xis increased to 3 times how will it affect the rate of formation of Y.
Answer :The rate will increase 9 times.

Question. When rate of reaction becomes equal to specific reaction rate.
Answer :When the concentration of reactant is Unity.

Question. 87.5% of the substance disintegrated in 45 minutes(first order reaction) .What is its Half life.
Answer :15 Minutes.

Important Questions for NCERT Class 12 Chemistry Chemical Kinetics

Question. In a zero-order reaction, for every 10 °C rise of temperature, the rate is doubled. If the temperature is increased from 10 °C to 100 °C, the rate of the reaction will become
(a) 256 times
(b) 512 times
(c) 64 times
(d) 128 times.

Question. The rate of the reaction,
2NO + Cl₂ → 2NOCl is given by the rate equation, rate = k[NO]₂[Cl₂]. The value of the rate constant can be increased by
(a) increasing the temperature
(b) increasing the concentration of NO
(c) increasing the concentration of the Cl₂
(d) doing all of these.

Question. The activation energy for a simple chemical reaction A ⇌ B is Ea in forward direction. The activation energy for reverse reaction
(a) is negative of Ea
(b) is always less than Ea
(c) can be less than or more than Ea
(d) is always double of Ea. 

Question. When a biochemical reaction is carried out in laboratory, outside the human body in absence of enzyme, then rate of reaction obtained is 10^–6 times, the activation energy of reaction in the presence of enzyme is
(a) 6/RT
(b) P is required
(c) different from Ea obtained in laboratory
(d) can’t say anything. 

Question. How enzymes increases the rate of reactions?
(a) By lowering activation energy
(b) By increasing activation energy
(c) By changing equilibrium constant
(d) By forming enzyme substrate complex

Question. Activation energy of a chemical reaction can be determined by
(a) evaluating rate constants at two different temperatures
(b) evaluating velocities of reaction at two different temperatures
(c) evaluating rate constant at standard temperature
(d) changing concentration of reactants. 

Question. By the action of enzymes, the rate of biochemical reaction
(a) does not change
(b) increases
(c) decreases
(d) either (a) or (c).

Question. An increase in the concentration of the reactants of a reaction leads to change in
(a) activation energy
(b) heat of reaction
(c) threshold energy
(d) collision frequency.

Question. For a chemical reaction represented by R → P the rate of reaction is denoted by –d [R]/dt or +d[P]/dt . State the significance of plus and minus sign.
Answer :(–) sign represents decrease in concentration with time while (+) sign represetns increase in concentration.

Question. Express the rate of reaction in terms of disappearance of hydrogen and appearance of ammonia in the given reaction.
Answer :N₂(g) + 3 H₂ (g) → 2NH₃ (g)
Rate= -1/3d[H₂]/dt rate=+1/2d[NH₃]/dt

Question. Why rate of reaction does not remain constant throughout?
Answer :It is because concentration of reactants goes on decreasing with time.

4. Write the unit of first order rate constant of a gaseous reaction if thepartial pressure of gaseous reactant is given in bar.
Answer :s^-1

Question. What will be the order of reaction, if the rate of reaction does not depend on the concentration of any of the reactant.
Answer :zero order

Question. For the elementary step of a chemical reaction : H₂ + I₂ →2HI rate of reaction →[H₂] [I₂] What is the (i) molecularity and (ii) order of the reaction.
Answer :i) 2 ii) 1

Question. For a chemical reaction A→ B. The rate of the reaction is given as Rate = k [A]ⁿ the rate of the above reaction quadruples when the concentration  of A is doubled. What is the value of n?
Answer :n=2

Question. Mention one example of zero order reaction.
Answer :2NH₃ (g)→N₂ (g) +3H₂(g) (at1130K and Pt as catalyst)

Question. What is the value of the order of reaction of radioactive decay?
Answer :First order

Question. Express the relation between the half life period of a reactant and initial concentration for a reaction of nth order.
Answer :t_1/2 α 1/[R]0^n-1 where n is order of reaction.

Question. A reaction is 50% complete in 2 hours and 75% complete in 4 hours. What is the order of reaction?
Answer :First order

Question. Suggest an appropriate reason for the observation : “On increasing temperature of the reacting system by 10 degrees, the rate of reaction almost doubles or even sometimes becomes five folds.”
Answer :Increasing the temperature of the substance increases the fraction of molecules which collide with energy greater than E_a.

Question. For a chemical reaction, activation energy is zero and at 300K rate constant is 5.9 × 10^-5s^–1, what will be the rate constant at 400K?
Answer :5.9 × 10^–5 s^–1

Question. Two reactions occuring at the same temperature have identical values of Ea. Does this ensure that also they will have the same rate constant? Explain.
Answer :No,because the Rate depends on the nature and concentrations of reactants and also pre-exponential factor.

Question. The rate constant of a reaction is given by the expression k = Ae–Ea/RT Which factor in this expression should register a decrease so that the reaction proceeds rapidly?
Answer :E_a should. Deacrease. : Rate = k [AB₂] [C₂]; Order = 1 + 1 = 2]

Question. For a chemical reaction rate constant k = 5.3 × 10^-4mol L–1 s^–1, what will be the order of reaction?
Answer :zero order reaction

Question. Write the rate law and order for the following reaction :
Answer :AB₂ + C2→AB₂C + C (slow)
AB₂ + C→AB₂C (Fast)]
Rate = k [AB₂] [C₂]; Order = 1 + 1 = 2]

Question. The conversion of molecules X to Y follows second order kinetics.If concentration of Xis increased to 3 times how will it affect the rate of formation of Y.
Answer :The rate will increase 9 times.

Question. When rate of reaction becomes equal to specific reaction rate.
Answer :When the concentration of reactant is Unity.

Question. 87.5% of the substance disintegrated in 45 minutes(first order reaction) .What is its Half life.
Answer :15 Minutes.

Important Questions for NCERT Class 12 Chemistry Chemical Kinetics

Question. In a zero-order reaction, for every 10 °C rise of temperature, the rate is doubled. If the temperature is increased from 10 °C to 100 °C, the rate of the reaction will become
(a) 256 times
(b) 512 times
(c) 64 times
(d) 128 times.

Question. The rate of the reaction,
2NO + Cl₂ → 2NOCl is given by the rate equation, rate = k[NO]₂[Cl₂]. The value of the rate constant can be increased by
(a) increasing the temperature
(b) increasing the concentration of NO
(c) increasing the concentration of the Cl₂
(d) doing all of these.

Question. The activation energy for a simple chemical reaction A ⇌ B is Ea in forward direction. The activation energy for reverse reaction
(a) is negative of Ea
(b) is always less than Ea
(c) can be less than or more than Ea
(d) is always double of Ea. 

Question. When a biochemical reaction is carried out in laboratory, outside the human body in absence of enzyme, then rate of reaction obtained is 10^–6 times, the activation energy of reaction in the presence of enzyme is
(a) 6/RT
(b) P is required
(c) different from Ea obtained in laboratory
(d) can’t say anything. 

Question. How enzymes increases the rate of reactions?
(a) By lowering activation energy
(b) By increasing activation energy
(c) By changing equilibrium constant
(d) By forming enzyme substrate complex

Question. Activation energy of a chemical reaction can be determined by
(a) evaluating rate constants at two different temperatures
(b) evaluating velocities of reaction at two different temperatures
(c) evaluating rate constant at standard temperature
(d) changing concentration of reactants. 

Question. By the action of enzymes, the rate of biochemical reaction
(a) does not change
(b) increases
(c) decreases
(d) either (a) or (c).

Question. An increase in the concentration of the reactants of a reaction leads to change in
(a) activation energy
(b) heat of reaction
(c) threshold energy
(d) collision frequency.

Q1) Define a) rate of a reaction b) activation energy

Q2) The decomposition of PH3 follows the following reaction 4PH₃ → P₄ + 6H₂
Rate equation is → Rate = k [PH3]. The Half life of PH₃ is 37.9 sec at 120°C
a) How much time is required for 3/4th of PH₃ to decompose?
Ans [75.82 sec]
b) What fraction of the original sample of PH3 remains behind after one minute?
Ans [2.995]

Q3) Define a) order of reaction b) molecularity of a reaction

Q4) the rate of a reaction increases four times when the temperature changes from 300K to 320K. Find the activation energy. (R=8.314 J/K/mol)
Ans [35.34 KJ/mol]

Q5) A reaction is of first order in reactant A and of second order in reactant B. How is the rate of this reaction affected when a) conc. Of B alone is increased to 3 times? b) the conc. A as well as B are doubled?
Ans [9 times, 8 times]

Q6) The rate constant for a reaction of zero order in A is 0.0030 mol/L/s. How long will it take for the initial conc. Of A to fall from 0.1 → 0M to 0.75M?
Ans [8.3sec]

Q7) Identify the order from units →L/mol/s

Q8) What are elementary reactions? Give examples.

Q9) A first order reaction has a rate constant of 0.0051 min^-1. If we begin with 0.10M conc. Of reactant, what conc. of reactant will remain in the solution after 3 hours?
Ans [0.04M]

Q10) H₂O₂ (aq) decomposes to H₂ O (l) and O₂ (g) in a reaction that is of first order in H₂O₂ and has a rate constant k=1.06 × 10^-3 min^-1. a) How long will it take 15% of a sample of H₂O₂ to decompose?
Ans [153.4 min]
b) How long will it take 85% of sample of H2O2 to decompose?
Ans [1790 min]

Q11) Why does the rate of a reaction not remain constant throughout the reaction process?

Q12) Show that for first order reaction half life is independent of initial conc.?

Q13) A first order decomposition reaction takes 40 min for 30% decomposition. Calculate t_1/2.

Q14) The decomposition of NH3 on Pt surface is zero order reaction. What are the rates of production of N₂ and H₂ if K= 2.5 × 10_-4 mol/L/s.

Q15) For a first order reaction, it takes for the initial conc. Of 0.6 mol/L to become 0.4 mol/L. How long will it take for the initial conc. To become 0.3 mol/L?
Ans [8.55 min]

Q16) A first order reaction takes 100 min for completion of 60% of the reaction. Find the time when 90% of the reaction will be completed?
Ans [251.3 min]

Q17) The slope of the line for the graph of LogK v/s 1/T for the reaction N₂O5→2NO₂ + ½ O₂ is -5000. Find activation energy.
Ans [95.7 KJ/mol]

Q18) For a reaction, activation energy is zero. What is the value of the rate constant at 300K if K= 1.6 × 10⁶ sec^-1 at 280K.

Q19) Find t_2/3 of a first order reaction in which K=5.4 × 10^-14 sec^-1?
Ans [0.2005 × 10¹⁴ sec]

Q20) The decomposition of phosphine: 4PH₃ → P₄ + 6H₂ has the rate law expression, Rate=K [PH₃]. The rate constant is 6.0 × 10^-4 sec^-1 at 300K and activation energy = 3.05 × 10⁵ J/mol. Find rate constant at 310K. R= 8.314 J/K/mol.
Ans [3.1 × 10^-2 sec^-1]

Q21) Show that the time required for the completion of ¾ of first order reaction is twice the time required for the completion of half of the reaction.

Q22) The reaction SO₂Cl₂ → SO₂ + Cl₂ is a first order reaction with K=2.2 × 10^-5 sec^-1 at 320°C. Find the percentage of SO₂Cl₂ that is decomposed on heating this gas for 30 minutes.
Ans [3.84%]

Important Questions for NCERT Class 12 Chemistry Chemical Kinetics

Question. For reaction aA→ xP , when [A] = 2.2 mM, the rate was found to be 2.4 mMs–1. On reducing concentration of A to half, the rate changes to 0.6 mMs–1. The order of reaction with respect to A is : 
(a) 1.5
(b) 2.0
(c) 2.5
(d) 3.0

Answer   B

Question. For a first order reaction, to obtain a positive slope, we need to plot {where [A] is the concentration of reactant A} 
(a) – log10[A] vs t
(b) – loge[A] vs t
(c) log10[A] vs log t
(d) [A] vs t

Answer   B

Question. T50 of first -order reaction is 10 min. Starting with 10 mol L^–1, rate after 20 min is 
(a) 0.0693 mol L^–1 min^–1
(b) 0.0693 × 2.5 mol L^–1 min^–1
(c) 0.0693 × 5 mol L^–2 min^–1
(d) 0.0693 × 10 mol L^–1 min^–1

Answer   B

Question. The first order rate constant for a certain reaction increases from 1.667 × 10–6 s^–1 at 727ºC to 1.667 × 10^–4 s^–1 at 1571ºC. The rate constant at 1150ºC, assuming constancy of activation energy over the given temperature range is
[Given : log 19.9 = 1.299] 
(a) 3.911 × 10^–5 s^–1
(b) 1.139 × 10^–5 s^–1
(c) 3.318 × 10^–5 s^–1
(d) 1.193 × 10^–5 s^–1

Answer   C

Question. In most cases, for a rise of 10K temperature the rate constant is doubled to tripled. This is due to the reason that
(a) collision frequency increases by a factor of 2 to 3.
(b) fraction of molecules possessing threshold energy increases by a factor of 2 to 3
(c) Activation energy is lowered by a factor of 2 to 3.
(d) none of these

Answer   B

Question. The rate constant for the reaction, 2N₂O₅ →4NO₂ +O₂ is 3.0x10^-4 s^-1 . If start made with 1.0 mol L^–1 of N₂O₅, calculate the rate of formation of NO₂ at the moment of the reaction when concentration of O₂ is 0.1 mol L^–1.
(a) 2.7 x10^-4 molL^-1s^-1 
(b) 2.4x10^-4  molL^-1s-1
(c) 4.8x10^-4  molL^-1s-1
(d) 9.6x10^-4  molL^-1s-1

Answer   D

Question. A reaction which is of first order w.r.t. reactant A, has a rate constant 6 min–1. If we start with [A] = 0.5 mol L^–1, when would [A] reach the value of 0.05 mol L^–1
(a) 0.384 min
(b) 0.15 min
(c) 3 min
(d) 3.84 min

Answer   A

Question. Half-lives of a first order and a zero order reaction are same. Then the ratio of the initial rates of first order reaction to that of the zero order reaction is 
(a) 1/0.693
(b) 2 × 0.693
(c) 0.693
(d) 2/0.693

Answer   B

Question. Collision theory is used to explain how chemical species undergo a reaction. Using this theory and the kinetic molecular model, which of the following does NOT influence the rate of a chemical reaction?
(a) The temperature of the system
(b) The geometry or orientation of the collision
(c) The velocity of the reactants at the point of collision
(d) All of the above influence the rate

Answer   D

Question. For the following reaction: NO₂(g) + CO(g) → NO(g) + CO₂(g), the rate law is: Rate = k [NO₂]₂.
If 0.1 mole of gaseous carbon monoxide is added at constant temperature to the reaction mixture which of the following statements is true?
(a) Both k and the reaction rate remain the same
(b) Both k and the reaction rate increase
(c) Both k and the reaction rate decrease
(d) Only k increases, the reaction rate remain the same

Answer   A