Activated Complex Theory & Collision Theory
MCQs for CSIR NET & GATE
Chemical Kinetics
Topic wise MCQs assignment-6
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 Ã… and 3.6 Ã… 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