Chemical Kinetics VBQs Class 12 Chemistry

VBQs for Class 12

VBQs Electrochemistry Class 12 Chemistry with Electrochemistry has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Chemistry with Electrochemistry. The following Electrochemistry Class 12 Chemistry value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Electrochemistry VBQs Class 12 Chemistry

Question. Two plots are shown below between concentration and time t. Which of the given orders are shown by the graphs respectively?

Chemical Kinetics VBQs Class 12 Chemistry

(a) Zero order and first order
(b) First order and first order
(c) First order and zero order
(d) None of these

Answer

A

Question. The following data were obtained during the first order thermal decomposition of SO2Cl2 at a constant volume.
SO2Cl2(g) → SO2(g) + Cl2(g)
Experiment       Time/s–1    Total pressure/atm
   1                     0                 0.5
   2                    100              0.6
What is the rate of reaction when total pressure is 0.65 atm?
(a) 0.35 atm s–1
(b) 2.235 × 10–3 atm s–1
(c) 7.8 × 10–4 atm s–1
(d) 1.55 × 10–4 atm s–1

Answer

C

Question. For the reaction, A + B → C following data has been observed
From the following data for the reaction between A and B.

Chemical Kinetics VBQs Class 12 Chemistry

The incorrect option about this reaction is
(a) the order of reaction with respect to A is 2
(b) the order of reaction with respect to B is 1
(c) the rate constant for the given reaction is 2.67 × 105 mol–2 L2 s–1
(d) none of these.

Answer

C

Question. A first order reaction is 20% complete in 10 minutes. What is the specific rate constant for the reaction?
(a) 0.0970 min–1
(b) 0.009 min–1
(c) 0.0223 min–1
(d) 2.223 min–1

Answer

C

Question. For a first order reaction, [A] = [A]0 e–kt concentration of reactant decreases exponentially with time. and t1/2 = 0.693/k
This relation shows that half-life is independent of concentration and t1/2 decreases with the increase of temperature
For first order reaction,
2N2O5(g) → 4NO2(g) + O2(g)
The reaction proceeds to 99.6% completion in
(a) 2 half lives
(b) 6 half lives
(c) 8 half lives
(d) 5 half lives

Answer

C

Question. In a pseudo first order hydrolysis of ester in water, the following results were obtained.

Chemical Kinetics VBQs Class 12 Chemistry

What will be the average rate of reaction between the time interval 30 to 60 seconds?
(a) 1.91 × 10–2 s–1
(b) 4.67 × 10–3 mol L–1 s–1
(c) 1.98 × 10–3 s–1
(d) 2.07 × 10–2 s–1 

Answer

B

Question. For the reaction N2 + 3H2 → 2NH3, how are the rate of reaction expressions inter-related

Chemical Kinetics VBQs Class 12 Chemistry
Answer

A

Question. For the reaction 2NH3 → N2 + 3H2, if

Chemical Kinetics VBQs Class 12 Chemistry

then the relation between k1, k2 and k3 is
(a) k1 = k2 = k3
(b) k1 = 3k2 = 2k3
(c) 1.5k1 = 3k2 = k3
(d) 2k1 = k2 = 3k3.

Answer

C

Question. The decomposition of dinitrogen pentoxide (N2O5) follows first order rate law. What will be the rate constant from the given data?
At t = 800 s, [N2O5] = 1.45 mol L–1
At t = 1600 s, [N2O5] = 0.88 mol L–1
(a) 3.12 × 10–4 s–1
(b) 6.24 × 10–4 s–1
(c) 2.84 × 10–4 s–1
(d) 8.14 × 10–4 s–1

Answer

B

Question.What will be the rate equation for the reaction 2X + Y → Z, if the order of the reaction is zero?
(a) Rate = k[X][Y]
(b) Rate = k
(c) Rate = k[X]0[Y]
(d) Rate = k[X][Y]0

Answer

B

Question. The overall rate of a reaction is governed by
(a) the rate of fastest intermediate step
(b) the sum total of the rates of all intermediate steps
(c) the average of the rates of all the intermediate steps
(d) the rate of slowest intermediate step. 

Answer

D

Question. In a first order reaction the concentration of reactant decreases from 400 mol L–1 to 25 mol L–1 in 200 seconds. The rate constant for the reaction is
(a) 1.01386 s–1
(b) 2 × 10–4 s–1
(c) 1.386 × 10–2 s–1
(d) 3.4 × 10–4 s–1

Answer

C

Question. A student of class-12, Jayesh did few experiments for the reaction,
2N2O5(g)  →  2N2O4(g) + O2(g)
and he plotted time against total pressure

Chemical Kinetics VBQs Class 12 Chemistry

If this reaction follows first order kinetics, value of rate constant k is
(a) 5.96 × 10–3 s–1
(b) 4.98 × 10–4 s–1
(c) 4.13 × 10–3 s–1
(d) 5.85 × 10–4 s–1

Answer

B

Question. Priyanshi after learning chemical kinetics chapter in class, she made notes for zero order and first order reactions as given below:

Chemical Kinetics VBQs Class 12 Chemistry

But the made few mistakes. Identify the wrong listed equations.
(a) Only I and III
(b) Only I and II
(c) Only IV
(d) III and IV 

Answer

D

Question. The expression to calculate time required for completion of zero order reaction is

Chemical Kinetics VBQs Class 12 Chemistry
Answer

A

Question. Rate of reaction is the change in concentration of any one of the reactants or products per unit time.
For a hypothetical reaction, A → B

Chemical Kinetics VBQs Class 12 Chemistry

In a reaction, A + 2B → 3C + 2D, the concentration of A decreases from 0.5 mol/L to 0.35 mol/L in 15 seconds. Then a student Ajinkya calculated following rates :
I. Rate of formation of C is 0.03 mol/L-s.
II. Rate of formation of D is 0.025 mol/L-s.
III. Rate of disappearance of B is 0.02 mol/L-s.
Which is/are incorrect statement(s)?
(a) I only
(b) II only
(c) II & III both
(d) I & III both

Answer

B

Assertion and Reason Based MCQs

Directions: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).
Mark the correct choice as:
(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.

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

Answer

A

Question. Assertion (A): Dust particles suspended in the air inside grain elevators (unheated) can sometimes react explosively.
Reason (R): The dust particles have large surface area for the reaction. 

Answer

B

Question. Assertion (A): Rate of reaction doubles when concentration of reactant is doubled if it is a first order reaction.
Reason (R): Rate constant also doubles with twice increase in the concentration of reactant.

Answer

C

Question. Assertion (A): For a first order reaction, half-life period is independent of initial concentration of the reacting species.
Reason (R): The half-life of a reaction is the time in which the reactant concentration is reduced to one half of its initial concentration. 

Answer

B

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

Answer

B

Question. Assertion (A): The rate of reaction increases with the increase in temperature.
Reason (R): The reactant molecules collide less frequently on increasing temperature. 

Answer

C

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

Answer

B

Question. 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.

Answer

B

SHORT ANSWER TYPE QUESTIONS

Question. The rate constant for first order reaction is 60/s. How much time will it take to reduce the concentration of the reaction to 1/10 of its initial value ?
Answer.

Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry

Question. The rate of most of reaction double when their temperature is raised from 298 K to 308 K. Calculate the activation energy of such a reaction.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry

Question. A first order reaction takes 69.3 min for 50% completion. Set up on equation for determining the time needed for 80% completion.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry

Question. The activation energy of a reaction is 94.14 KJ/mol and the value of rate constant at 40º C is 1.8 × 10-1 sec-1. Calculate the frequency factor A.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry

Question. The rate constant of a reaction at 500 K and 700 K are 0.02 s-1 and 0.07 s-1 respectively. Calculate the value of Ea and A.
Answer. 18.23 KJ mol-1, 1.603

Question. The rate constant of a reaction at 700 K and 760 K are 0.011 M-1 s-1 and 0.105 M-1 s-1 respectively. Calculate the value of Arrhenius parameters.
Answer. 2.824 × 1010

Question. The initial concentration of N2O5 in the first order reaction N2O5 → 2NO2+ ½O2 was 1.24 × 10-2 mol L-1 at 318 K. The concentration of N2O5 after 60 minutes was 0.20 × 10-2 mol L-1. Calculate the rate constant of the reaction at 318 K.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry

Question. The following data were obtained during the first order thermal decomposition of N2O5 at constant volume :
2N2O5 → 2N2O4 + O2

Chemical Kinetics VBQs Class 12 Chemistry

Calculate rate constant.
Answer. 4.98 × 10−4 sec-1

Question. A first order reaction is 20% complete in 20 minutes. Calculate the time taken for the reaction to go to 80% completion.
Answer. 144.3 minutes

Question. For a first order reaction, calculate the ratio between the time taken to complete ¾ of the reaction and the time taken to complete half of the reaction.
Answer. Two

Question. The following results have been obtained during the kinetics studies of the reaction :
2A + B → C + D

Chemical Kinetics VBQs Class 12 Chemistry

Determine the rate law and the rate constant for the reaction.
Answer. Rate = K[A][B]2

Question. The decomposition of A into product has value of K as 4.5 × 103 sec-1 at 10º C and energy of activation 60 kJ/mol. At what temperature would K be 1.5 × 104 sec-1.
Answer. 24º C

Question. (a) Write rate law and order of the following reaction :
AB + C2 → AB2C + C (slow)
AB2 + C → AB2C (fast)
(b) Define energy of activation of a reaction.
(c) What is the relationship between rate constant and activation energy of a reaction ?
Answer. (a) Rate = K[AB][C2], Order = 1 + 1 = 2

Question. In a pseudo first order reaction of hydrolysis of an ester in H2O, the following results were obtained :

Chemical Kinetics VBQs Class 12 Chemistry

(a) Calculate the average rate of reaction between the time interval 30 to 60 sec.
(b) Calculate the pseudo first order rate constant for the hydrolysis of ester.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry

Question. The decomposition of NH3 on platinum surface is a zero order reaction.
What are the rate of production of N2 and H2 ? [K = 2.5 × 10−4]
Answer.

Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry

LONG ANSWER TYPE QUESTIONS

Question. (a) Define order of reaction.
(b) Rates of reaction double with every 10º rise in temperature. If this generalization holds for a reaction in the temperature ranges 298 K to 308 K, what would be the value of activation energy for their reaction ?
R = 8.314 J K-1 mol-1.
Answer. (a) Order of Reaction : It is the sum of powers to which the conc. terms are raised in rate law expression.

Chemical Kinetics VBQs Class 12 Chemistry

Question. (a) What are pseudo order reaction ? Give example.
(b) Rate constant K of a reaction varies with temperature ‘T’ according to the equation :

Chemical Kinetics VBQs Class 12 Chemistry

where Ea is the activation energy. When a graph is plotted for log K vs 1/T, a straight line with a slope of − 4250 K is obtained. Calculate Ea for the reaction.
Answer. (a) The chemical reaction which look like higher order reaction but in real they follow lower order kinetics.
For example,

Chemical Kinetics VBQs Class 12 Chemistry

Question. (a) Determine the units of rate constant for first and zero order reaction.
(b) Show that time required for the completion of 99% of the first order reaction is twice the 90% of completion of the reaction.
Answer.

Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry

Question. (a) Define rate constant of reaction.
(b) A first order reaction takes 40 mins for 30% decomposition. Calculate t½.
Answer. (a) Rate constant : It is the rate of chemical reaction when the concentration of reactant taken as unity at a given temperature.
(b) Let initial conc. = a

Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry

Question. (a) Determine the order of reaction and also determine the units of rate constant.

Chemical Kinetics VBQs Class 12 Chemistry

(b) The following data were given for thermal decomposition of SO2Cl2 at a constant volume :

Chemical Kinetics VBQs Class 12 Chemistry

Calculate the rate of the reaction when total pressure is 0.65 atm.
Answer. 

Chemical Kinetics VBQs Class 12 Chemistry
Chemical Kinetics VBQs Class 12 Chemistry

Question. (a) The activation energy of a reaction is 100 kJ/mol. In the presence of catalyst the activation energy is decreased by 75%. What is the effect on rate constant of the reaction at 20º C ?
(b) A + 2B → 3C + 2D
The rate of disappearance of B is 1 × 10–2 mol L–1 sec–1. What will be
(i) rate of reaction (ii) rate of change in the concentration of A and C ?
Answer. 

Chemical Kinetics VBQs Class 12 Chemistry