Activated Complex Theory & Collision Theory | Chemical Kinetics | MCQs for CSIR NET & GATE - Download PDF

Vijay Ishwar
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Activated Complex Theory & Collision Theory
MCQs for CSIR NET & GATE

Chemical Kinetics
Topic wise MCQs assignment-6

QUIZ        PDF

Q1. For the reaction, A + B X++, Ea= 20.0 KJ/mol at 300 K. The enthalpy change for the formation of the activated complex from the reactants in KJ/mol is

[GATE 2004]

            (a) 12

            (b) 15

            (c) 23

            (d) 25

Q2. Consider the unimolecular reaction

A(g) Products

For which the following remarks were made.

A) The reaction is second order at low pressure and becomes first order at high pressure

B) The reaction is first order at low pressure and becomes second order at high pressure

C) The reaction is zero order.

Which of these is/are correct

            (a) A and B

            (b) B and C

            (c) only C

            (d) only A

Q3. Consider the reaction,

H2 + C2H4 C2H6

[GATE 2012]

The molecular diameters of H2 and C2H4 are 1.8 Å and 3.6 Å respectively. The pre-exponential factor in the rate constant calculated using collision theory in m3 (mole)-1 s-1 is approximately? (For this reaction at 300 K, (8kBT/πμ)1/2 NA = 1.11 x 1027 m (mole)-1 s-1 where the symbols have their usual meanings)

            (a) 2.5x108

            (b) 2.5x1014

            (c) 9.4x1017

            (d) 9.4x1023

Q4. The rate constant of a unimolecular reaction was 2.66x10-3 s-1 and 2.2x10-1 s-1 at T=120 K and 360 K respectively. The rate constant (in s-1 units) at 240 K would be

            (a) 2.4 x 10-2

            (b) 2.4 x 10-1

            (c) 4.8 x 10-2

            (d) 1.8 x 10-3

Q5. In the collision theory, the pre-exponential factor is

            (a) independent of temperature

            (b) proportional to temperature

            (c) proportional to square of temperature

            (d) proportional to square root of temperature

Q6. According to conventional transition state theory, for elementary bimolecular reaction, the molar entropy of activation ΔS# is

[GATE 2011]

            (a) positive

            (b) zero

            (c) negative

            (d) positive for endothermic and negative for exothermic reactions.

Q7. One of the assumptions made in the conventional activated complex theory is

[NET June 2012]

(a) equilibrium is maintained between reactants and the activated complex.

(b) equilibrium is maintained between the reactants and the products.

(c) equilibrium is maintained between the products and the activated complex.

(d) equilibrium is maintained between the reactants, the activated complex and the products.

Q8. The Arrhenius parameters for the thermal decomposition of NOCl,

[NET Dec 2012]

2 NOCl (g) 2 NO (g) + Cl2 (g)

are A=1013 M-1 s-1, Ea=105 KJ mol-1 and RT=2.5 KJ mol-1. The enthalpy (in KJ mol-1) of the activated complex will be

            (a) 110

            (b) 105

            (c) 102.5

            (d) 100

Q9. Observe the following statements

[NET June 2013]

I) In the H2-O2 reaction, explosion occurs when the rate of chain branching exceeds that of chain termination.

II) The order of the reaction, nA products, is 2.5. For this reaction, t1/2 [A]o-3/2

III) unimolecular gas phase reactions are second order at low pressure but becomes first order at high pressure.

Which statements are correct?

            (a) I, II and III are correct

            (b) only II are correct

            (c) only III are correct

            (d) only I and II are correct

Q10. In the Lindemann mechanism of unimolecular reactions, the observed order at low concentration is

[NET June 2013]

            (a) 0.5

            (b) 1

            (c) 1.5

            (d) 2

Q11. For a gas phase unimolecular reaction at temperature 298 K, with a pre-exponential factor of 2.17x1013 s-1, the entropy of activation (JK-1mol-1) is ______

[GATE 2015]

Q12. The first order rate constant for a unimolecular gas phase reaction, A to products that follows Lindemann mechanism is 2.0 s-1 at pA=1 atm and 4.0 s-1 at pA= 2 atm. The rate constant for the activation step is

[NET Dec 2015]

            (a) 1.0 atm-1 s-1

            (b) 2.0 atm-1 s-1

            (c) 4.0 atm-1 s-1

            (d) 8.0 atm-1 s-1

Q13. For an elementary bimolecular gas phase reaction, activation energy is 5.5 KJ mol-1. Enthalpy of activation in KJ mol-1, at 300 K is _________ (R=8.314 J K-1 mol-1)

[GATE 2016]

Q14. According to transition state theory, the plot with slope equal to -ΔH#/R is

            (a) ln k vs T

            (b) ln(k/T vs T)

            (c) ln k/T vs 1/T

            (d) ln k vs 1/T

Q15. For two reactions,

X(g) + Y(g) Z(g)                (1)

M(g) + N(g) P(g)              (2)

According to collision theory, the ratio of squares of pre exponential factors of reactions 2(A2) and 1(A1) at the same temperature is (A2/A1)2

            (a) 4/5

            (b) 5/5

            (c) 5/3

            (d) 3/5

Ans Key:

Q1.a Q2.d Q3.a Q4.a Q5.d Q6.c Q7.a Q8.d Q9.a Q10.d Q11.2.0 to 2.5 Q12.b Q13.0.5 Q14.c Q15.a

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