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#### Chemical Kinetics Model Question Paper

12th Standard EM

Reg.No. :
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Chemistry

Time : 01:00:00 Hrs
Total Marks : 50
12 x 1 = 12
1. The decomposition of phosphine (PH3) on tungsten at low pressure is a first order reaction. It is because the (NEET)

(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 slow

2. For a reaction Rate = kacetone[]32 then unit of rate constant and rate of reaction respectively is

(a)

(mol L-1 S-1),(mol1/2L1/2S-1)

(b)

(mol-1/2L1/2s-1),(mol L-1s-1)

(c)

(mol1/2L1/2s-1),(molL-1s-1)

(d)

(molLs-1),(mol1/2L1/2s)

3. In a first order reaction $x\longrightarrow y$ if k is the rate constant and the initial concentration of the reactant x is 0.1M, then, the half life is

(a)

$\left( \cfrac { log2 }{ k } \right)$

(b)

$\left( \cfrac { 0.693 }{ (0.1)k } \right)$

(c)

$\left( \cfrac { In2 }{ k } \right)$

(d)

none of these

4. Predict the rate law of the following reaction based on the data given below
$2A+B\longrightarrow C+3D$

 Reaction number [A] (min) [B] (min) Initial rate (M s-1) 1 0.1 0.1 x 2 0.2 0.1 2x 3 0.1 0.2 4x 4 0.2 0.2 8x
(a)

rate=k[A]2[B]

(b)

rate=k[A][B]2

(c)

rate=k[A][B]

(d)

rate=k[A]1/2[B]1/2

5. During the decomposition of H2O2 to give dioxygen, 48 g O2 is formed per minute at certain point of time. The rate of formation of water at this point is

(a)

0.75 mol min−1

(b)

1.5 mol min−1

(c)

2.25 mol min−1

(d)

3.0 mol min−1

6. A+B $\longrightarrow$ C; ∆H = 60 kJ mol-1 Eaf = 150 kJ. What is the activation energy of the backward reaction?

(a)

210 kJ

(b)

105 kJ

(c)

90 kJ

(d)

145 kJ

7. (a)

It is a 2 steps reaction, step 1 is slower than step 2

(b)

It is a 2 steps reaction, step 2 is slower than step 1.

(c)

Single step reaction where B is a activated complex

(d)

Single step reaction in which B is a reaction intermediate.

8. Which order reaction obeys the expression ${ t }_{ \frac { 1 }{ 2 } }\alpha \frac { 1 }{ \left[ A \right] } ?$

(a)

First

(b)

Second

(c)

Third

(d)

Zero

9. The addition of a catalyst during a chemical reaction alters which of the following quantities?

(a)

Activation energy

(b)

Entropy

(c)

Internal energy

(d)

Enthalpy

10. Rate law cannot be determined from balanced chemical equation if _____________

(a)

Reverse reactions is not involved

(b)

It is an elementary reaction

(c)

It is a sequence of elementary reactions

(d)

All of the reactants is in excess. Rate law can be determined from balanced chemical equation if it is an elementary reaction.

11. The minimum energy that all colliding molecules must possess so as to make the collisions more effective and successful is_____________

(a)

activation energy

(b)

colliding energy

(c)

threshold energy

(d)

kinetic energy

12. Activation energy of a reactant is reduced by ___________________

(a)

increased temperature

(b)

reduced temperature

(c)

increased pressure

(d)

reduced pressure

13. 1 x 1 = 1
14. Two reactions A ⟶ Band C ⟶ D has the energy of activation 40 kJ and 60 kJ respectively. Which of the following statement is correct?
a) Comparison of rate cannot be determined
b) The reaction A ⟶ B proceeds at a faster rate compared to the reaction C ⟶ D
c) The reaction A ⟶ B proceeds at a slower rate compared to the reaction C ⟶ D.
d) Comparison of rate cannot be determined.

()

b) The reaction A ⟶ B proceeds at a faster rate compared to the reaction C ⟶ D

15. 3 x 2 = 6
16. Assertion: A positive catalyst increases the rate of reaction.
Reason: A positive catalyst alters reaction mechanism and decreases activation energy.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false.
d) Both assertion and reason are false.

17. Assertion: Order and molecularity are same.
Reason: Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of rate determining elementary step.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false.
d) Both assertion and reason are false.

18. Assertion: A catalyst is a substance which alters the rate of a reaction. Reason: In the presence of catalyst the energy of activation is increased.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false.
d) Both assertion and reason are false.

19. 1 x 2 = 2
20. Consider the following statements and identify the incorrect statement(s).
(i) Decomposition of H2O2 is an II order reaction
(ii) t1/u  is independent of initial concentration of a reaction.
(iii) Fractional order reactions are observed depending on their rates.
(iv) Rate = k [A]p [B]q; p + q = order.
a) only (ii)
b) both (ii) and (iii)
c) only (i)
d) None of these

21. 4 x 2 = 8
22. Define half life of a reaction. Show that for a first order reaction half life is independent of initial concentration

23. Describe the graphical representation of first order reaction.

24. For a chemical reaction, Variation in the concentration In[A] Vs time in seconds is given as

(i) What is the order of the reaction?
(ii) What is the unit of rate constant K?
(iii) Give the relationship between k and ${ t }_{ \frac { 1 }{ 2 } }$

25. If the rate of a reaction gets doubled as the temperature is increased from 27oC to 37oC. Find the activation energy of reaction?

26. 2 x 3 = 6
27. A reaction is of second order in A and first order in B.
(i) Write the differential rate equation.
(ii) How is the rate affected on increasing the concentration of A three times?
(iii) How is the rate affected when the concentration of both A and B is doubled?

28. From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.
(i) 3NO(g) ⟶ N2O(g) Rate = K[NO]2
(ii) H2O2(aq) + 3I-(aq) +2H+ ⟶ 2H2O(l) +I3- Rate = K[H2O2][I-]
(iii) CH3CHO(g) ⟶ CH4(g) +CO(g) Rate = K[CH3 CHO]3/2
(iv) C2H5Cl(g) ⟶ C2H2(g) +HCl(g) Rate = K[C2H5Cl]2

29. 3 x 5 = 15
30. The time for half change in a first order decomposition of a substance A is 60 seconds. Calculate the rate constant. How much of A will be left after 180 seconds?

31. Benzene diazonium chloride in aqueous solution decomposes according to the quation ${ C }_{ 6 }{ H }_{ 5 }{ N }_{ 2 }Cl\longrightarrow { C }_{ 6 }{ H }_{ 5 }Cl+{ N }_{ 2 }$ Starting with an initial concentration of 101 g L-1, the volume of N2 gas obtained at 50 °C at different intervals of time was found to be as under:

 t(min) 6 12 18 24 30 $\infty$ Vol.of N2 (ml) 19.3 32.6 41.3 46.5 50.4 58.3

Show that the above reaction follows the first order kinetics. What is the value of the rate constant?

32. The initial rate of a first order reaction is 5.2 x 10-6 mol lit-1 S-1 at 298 K. When the initial concentration of reactant is 2.6 x 10-3 mol.lit-1, calculate the first order rate constant of the reaction at the same temperature.