# MCQ | Chemical Kinetics

QUIZ – I

Q:1. A first order reaction is 87.5% complete in an hour. The rate constant of the
reaction is

(A) 0.0346 min–1

(B) 0.0693 h–1

(C) 0.0693 min–1

(D) 0.0346 h–1

Ans: (A)

Q:2.The half -life a first order reaction is 24 hours. If we start with 10 M initial concentration of the reactant then conc. after 96 hours will be

(A) 6.25 M

(B) 1.25 M

(C) 0.125 M

(D) 0.625 M

Ans: (D)

Q:3. During the particular reaction 10% of the reactant decompose in one hour 20% in two hours 30% in three hours and so on. The unit of the rate constant is

(A) Hour–1

(B) L mol–1 hour–1

(C) mol L–1 hour–1

(D) mol hour–1

Ans: (C)

Q:4.The temperature coefficient of a reaction is 2, by what factor the rate of reaction increases when temperature is increased from 30°C to 80°C.

(A) 16

(B) 32

(C) 64

(D) 128

Ans: (B)

Q:5. The rate constant, the activation and Arrhenius parameter of a chemical reaction at 25°C are 3 × 10–4 s–1, 104.4 kJ mol–1 and 6 × 1014 s–1 respectively. The value of the rate constant at T → ∞ is

(A) 2 × 1018s–1

(B) 6 × 1014

(C) α

(D) 3.6 × 1030s–1

Ans: (B)

Q:6. At 250°C, the half life for the decomposition of N2O5 is 5.7 hour and is independent of initial pressure of N2O5. The specific rate constant is

(A) 0.693/5.7

(B) 0.693 × 5.7

(C)   5.7/0.693

(D) None

Ans: (A)

Q:7. For a given reaction of first order, it takes 20 min, for the concentration to drop from
1 M L–1 to 0.6 ML–1. The time required for the concentration to drop from 0.6 ML–1 to 0.36 ML–1 will be

(A) > 20 min

(B) < 20 min

(C) = 20 min

(D) ∞

Ans: (C)

Q:8. In a first order reaction the $\frac{a}{a-x}$ was found to be 8 after 10 min. The rate constant is

(A)   $\frac{2.303 \times 3 log2}{10}$

(B)  $\frac{2.303 \times 2 log3}{10}$

(C) 10 × 2.303 × 2 log 3

(D) 10 × 2.303 × 3 log 2

Ans: (A)

Q:9. For the reaction A + B ¾® Products, it si found that the order of A is 2 and of B is 3 in the rate expression. When concentration of both is doubled the rate will increase by

(A) 10

(B) 6

(C) 32

(D) 16

Ans: (C)

Q:10. The rate law of the reaction A + 2B → Product is given by d[Product]/dt = K[A]2×[B]. If A is taken in large excess, the order of the reaction will be

(A) 0

(B) 1

(C) 2

(D) 3

Ans: (B)

Q:11. If a reaction with t1/2 = 69.3 sec, has a rate constant 10–2 sec–1, the order is

(A) 0

(B) 1

(C) 2

(D) 3

Ans: (B)

Q:12. The specific rate constant for a first order reaction is 60 × 10–4 sec–1. If the initial concentration of the reactant is 0.01 mol L—1, the rate is

(A) 60 × 10–6 M sec–1

(B) 36 × 10–4 M sec–1

(C) 60 × 10–2 M sec–1

(D) 36 × 10–1 M sec–1

Ans: (A)

Q:13. The rate constant for a zero order reaction is 2 × 10–2 mol L–1 sec–1. If the concentration of the reactant after 25 sec is 0.5 M, the initial concentration must have been

(A) 0.5 M

(B) 1.25 M

(C) 12.5 M

(D) 1.0 M

Ans: (A)

Q:14. A first order reaction is carried out with an initial concentration of 10 ML–1 and 80% of the reactant changes into the product. Now if the same reaction is carried out with an initial concentration of 5 ML–1, the percentage of reactant changing to the product is

(A) 40

(B) 80

(C) 160

(D) can’t be calculated

Ans: (B)

Q:15. What fraction of a reactant showing first order remains after 40 min, if t1/2 is 20 min ?

(A) 1/4

(B) 1/2

(C) 1/8

(D) 1/6

Ans: (D)

Q:16. A substance undergoes a first order decomposition. The decomposition follows two parallel first order reaction as

The percentage distribution of B and C are

(A) 80% B and 20% C

(B) 75%  B and 25% C

(C) 90% B and 10% C

(D) 60% B and 40% C

Ans: (B)

Q:17. A tangent drawn on the curve obtained by plotting concentration of product
(mole L–1) of a first order reaction vs. time (min) at the point corresponding to time 20 minute makes an angle to 30° with concentration axis. Hence the rate of formations of product after 20 minutes will be

(A) 0.580 mole L–1 min–1

(B) 1.723  mole L–1 min–1

(C)  0.290 mole L–1 min–1

(D) 0.866 mole L–1 min–1

Ans: (B)

Q:18. For reaction 3A ¾® products, it is found that the rate of reaction increases 4- fold when concentration of A is increased 16 times keeping the temperature constant. The order of reaction is ?

(A) 2

(B) 1

(C) 1

(D) 0.5

Ans: (D)

Q:19. The thermal decomposition of acetaldehyde : CH3CHO → CH4 + CO, has rate constant of 1.8 × 10–3 mole–1/2L1/2 min–1 at a given temperature. How would will change if concentration of acetaldehyde is doubled keeping the temperature constant ?

(A) will increase by 2.828 times

(B) will increase by 11.313 times

(C)  will not change

(D) will increase by 4 times

Ans: (A)

Q:20. The reaction ; 2O3 → 3O2, is assigned the following mechanism.

(I) O3 $\rightleftharpoons$  O2 + O

(II) O3 + O $\rightarrow^{slow}$  2O2

The rate law of if the reaction will, therefore be

(A) r ∝ [O3]2[O2]

(B) r ∝ [O3]2 [O2]–1

(C)  r ∝ [O3]

(D) r ∝ [O3] [O2]–2

Ans: (D)

Q:21. For an endothermic reaction where ΔH represents the enthalpy of the reaction, the minimum value for the energy of activation will be

(A) Less than ΔH

(B) zero

(C) more than ΔH

(D) equal to ΔH

Ans: (C)

Q:22. The rate expression for a reaction is rate = k[A]3/2 [B]–1, the order of reaction is

(A) 0

(B) 1/2

(C) 3/2

(D) 5/2

Ans: (B)

Q:23. The reaction A(g) + 2B(g) → C(g) + D(g) is an elementary process. In an experiment, the initial partial pressure of A & 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

Ans: (D)

Q:24. If concentration are measured in mole/lit and time in minutes, the unit for the rate constant of a 3rd order reaction are

(A) mol lit–1 min–1

(B) lit2 mol–2min–1

(C) lit.mol–1 min–1

(D) min–1

Ans: (B)

Q:25. A radioactive element has a half life period of 140 days. How much of it will remain after 1120 days

(A)  1/32

(B) 1/250

(C)  1/512

(D) 1/128

Ans: (A)

Q:26. For a first order reaction the plot of log [A]t Vs t is linear with a

(A) positive slope and zero intercept

(B) positive slope and non zero intercept

(C) negative  slope and zero intercept

(D) negative slope and non zero intercept

Ans: (A)

Q:27. For a hypothetical reaction A + B → C+D, the rate = k[A]–1/2 [B]3/2. On doubling the concentration of A and B the rate will be

(A) 4 times

(B) 2 times

(C) 3 times

(D) none of these

Ans: (B)

Q:28. In a reaction the threshold energy is to equal to

(A) average energy of the reactants

(B) activation energy

(C) activation energy  + average energy of the reactants

(D) activation energy – average energy of the reactants

Ans: (B)

Q:29. For a first reaction t0.75 is 138.6 seconds. Its specific rate constant ( in sec–1) is

(A) 10–2

(B) 10–4

(C) 10–5

(D) 10–6

Ans: (C)

Q:30. Half life period for a first–order reaction is 10 minutes. How much time is required to change the concentration of the reactants from 0.08 M to 0.01 M

(A) 20 min

(B) 30 min

(C) 40 min

(D) 50 min