JEE Chemistry Chemical Kinetics MCQs Set 12

Multiple Choice Questions (MCQs) for JEE Chemistry: Chemical Kinetics

Review structured MCQ sets for JEE Chemistry Chemical Kinetics. Built according to official JEE guidelines, these downloadable questions support daily revision and core concept reinforcement.

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Multiple Choice Questions

Question 1: According to the collision theory of reaction rates
(a) every collision between reactants leads to a chemical reaction
(b) the rate of reaction is proportional to the velocity of molecules
(c) all reactions which occur in the gaseous phase are zero order
(d) the rate of reaction is directly proportional to the collision frequency
Show Answer & Explanation

Answer: (d) the rate of reaction is directly proportional to the collision frequency

Explanation:
1. Only collisions with enough energy and proper orientation are effective, so (a) is false.
2. Rate = (collision frequency) × (fraction of effective collisions), so the rate is proportional to collision frequency.

Teacher's Note:
1. Collision frequency Z and the Boltzmann factor e−Ea/RT both enter the rate.

Question 2: The activation energy of a reaction is
(a) the energy released during the reaction
(b) the energy evolved when the activated complex is formed
(c) the minimum extra amount of energy needed to overcome the potential barrier of the reaction
(d) the energy needed to form one mole of the product
Show Answer & Explanation

Answer: (c) the minimum extra amount of energy needed to overcome the potential barrier of the reaction

Explanation:
1. Activation energy is the energy that reactant molecules must acquire beyond their average energy to reach the transition state.

Teacher's Note:
1. Ea = threshold energy − average energy of reactants.

Question 3: At room temperature the reaction between NO and O2 to give NO2 is fast while that between CO and O2 is slow. This is due to
(a) CO being smaller in size than NO
(b) CO being poisonous
(c) the activation energy for 2NO + O2 → 2NO2 being less than that for 2CO + O2 → 2CO2
(d) NO2 being poisonous
Show Answer & Explanation

Answer: (c) the activation energy for 2NO + O2 → 2NO2 being less than that for 2CO + O2 → 2CO2

Explanation:
1. A lower activation energy means more molecules cross the barrier, so the rate is higher.

Teacher's Note:
1. Rate differences at the same temperature come from Ea.

Question 4: A chemical reaction occurs as a result of collisions between reacting molecules. Therefore, the reaction rate is given by
(a) total number of collisions occurring in a unit volume per second
(b) fraction of molecules which possess energy less than the threshold energy
(c) total number of effective collisions
(d) temperature
Show Answer & Explanation

Answer: (c) total number of effective collisions

Explanation:
1. Only effective collisions (enough energy and correct orientation) produce reaction.

Teacher's Note:
1. Total collisions is much larger than effective collisions.

Question 5: A large increase in the rate of a reaction for a rise in temperature is due to
(a) an increase in the number of collisions
(b) an increase in the number of activated molecules
(c) a lowering of activation energy
(d) a shortening of the mean free path
Show Answer & Explanation

Answer: (b) an increase in the number of activated molecules

Explanation:
1. Collision frequency rises only about 1 to 2% per 10 K, but the fraction of molecules with energy ≥ Ea roughly doubles.
2. Ea is not changed by temperature.

Teacher's Note:
1. The Maxwell-Boltzmann tail grows rapidly with temperature.

Question 6: The rate of which reactions increases with temperature?
(a) of any reaction
(b) of exothermic reactions
(c) of endothermic reactions
(d) cannot be predicted
Show Answer & Explanation

Answer: (a) of any reaction

Explanation:
1. Rate constant k = Ae−Ea/RT increases with T for every reaction that has positive Ea.

Teacher's Note:
1. This holds for both exothermic and endothermic reactions.

Question 7: The rate of a chemical reaction doubles for every 10°C rise in temperature. If the temperature is increased by 60°C, the rate of the reaction increases by
(a) 20 times
(b) 32 times
(c) 64 times
(d) 128 times
Show Answer & Explanation

Answer: (c) 64 times

Explanation:
1. 60°C rise = 6 steps of 10°C.
2. Rate increases by 26 = 64 times.

Teacher's Note:
1. Temperature coefficient = 2.

Question 8: According to the Arrhenius equation, a straight line is obtained by plotting the logarithm of the rate constant (log k) against
(a) T
(b) log T
(c) 1/T
(d) log (1/T)
Show Answer & Explanation

Answer: (c) 1/T

Explanation:
1. log k = log A − Ea/(2.303RT), linear in 1/T.

Teacher's Note:
1. Slope = −Ea/2.303R.

Question 9: Which plot gives the value of activation energy?
(a) k versus T
(b) 1/k versus T
(c) ln k versus T
(d) ln k versus 1/T
Show Answer & Explanation

Answer: (d) ln k versus 1/T

Explanation:
1. ln k = ln A − (Ea/R)(1/T): slope of ln k against 1/T = −Ea/R.

Teacher's Note:
1. Intercept gives ln A.

Question 10: If k is the rate constant for some order of any reaction at temperature T, then the value of limT→∞ log k is
(a) \( A/2.303 \)
(b) A
(c) 2.303 A
(d) log A
Show Answer & Explanation

Answer: (d) log A

Explanation:
1. As T → ∞, e−Ea/RT → 1, so k → A.
2. log k → log A.

Teacher's Note:
1. A is the pre-exponential factor (the limiting rate constant).

Question 11: For an endothermic reaction where ΔH represents the enthalpy of the reaction in kJ/mol, the minimum value for the energy of activation will be
(a) less than ΔH
(b) zero
(c) more than ΔH
(d) equal to ΔH
Show Answer & Explanation

Answer: (c) more than ΔH

Explanation:
1. For an endothermic reaction products lie above reactants by ΔH, and the barrier must exceed this: Ea > ΔH.

Teacher's Note:
1. For exothermic reactions Ea may be small or even zero.

Question 12: The rate of a reaction increases to 2.3 times when the temperature is raised from 300 K to 310 K. If k is the rate constant at 300 K, then the rate constant at 310 K will be equal to
(a) 2k
(b) 2.3k
(c) 3k
(d) k2
Show Answer & Explanation

Answer: (b) 2.3k

Explanation:
1. Rate constant is proportional to the rate at the same concentrations.
2. k310 = 2.3k.

Teacher's Note:
1. The rate constant scales by the same factor as the rate at fixed concentrations.

Question 13: If the concentration of reactants is increased by x, then k becomes
(a) \( \ln\dfrac{k}{x} \)
(b) \( \dfrac{k}{x} \)
(c) k + x
(d) k
Show Answer & Explanation

Answer: (d) k

Explanation:
1. The rate constant does not depend on concentration.

Teacher's Note:
1. Only the rate changes with concentration.

Question 14: For producing effective collisions, the colliding molecules must possess
(a) a certain minimum amount of energy
(b) energy equal to or greater than the threshold energy
(c) proper orientation
(d) threshold energy as well as proper orientation of collision
Show Answer & Explanation

Answer: (d) threshold energy as well as proper orientation of collision

Explanation:
1. Both conditions are required: energy ≥ threshold energy and correct orientation.

Teacher's Note:
1. The steric factor accounts for orientation.

Question 15: The activation energy for a chemical reaction depends upon
(a) temperature
(b) nature of the reacting species
(c) concentration of the reacting species
(d) collision frequency
Show Answer & Explanation

Answer: (b) nature of the reacting species

Explanation:
1. Ea is characteristic of the reaction (and catalyst), and independent of concentration, and essentially of temperature.

Teacher's Note:
1. A catalyst lowers Ea.

Question 16: The rate constants of two reactions are k1 = 1016 e−2000/T and k2 = 1015 e−1000/T. The temperature at which k1 = k2 is
(a) \( \dfrac{2000}{2.303}\ \text{K} \)
(b) 2000 K
(c) \( \dfrac{1000}{2.303}\ \text{K} \)
(d) 1000 K
Show Answer & Explanation

Answer: (c) \( \dfrac{1000}{2.303}\ \text{K} \)

Explanation:
1. 1016e−2000/T = 1015e−1000/T gives 10 = e1000/T.
2. ln 10 = 2.303 = 1000/T, so T = 1000/2.303 K.

Teacher's Note:
1. Take natural logarithms of both sides.

Question 17: The rate of the reaction 2NO + Cl2 → 2NOCl is given by rate = k[NO]2[Cl2]. The value of the rate constant can be increased by
(a) increasing the concentration of NO
(b) increasing the concentration of Cl2
(c) increasing the temperature
(d) doing all of these
Show Answer & Explanation

Answer: (c) increasing the temperature

Explanation:
1. The rate constant depends only on temperature (and catalyst).

Teacher's Note:
1. Concentration changes alter the rate, not k.

Question 18: Which of the following statements for the order of a reaction is incorrect?
(a) Order can be determined only experimentally
(b) Order is not influenced by stoichiometric coefficient of the reactants
(c) Order of a reaction is the sum of the powers to the concentration terms of the reactants in the rate law
(d) Order of a reaction is always a whole number
Show Answer & Explanation

Answer: (d) Order of a reaction is always a whole number

Explanation:
1. Order can be zero, fractional or even negative.
2. The other three statements are correct.

Teacher's Note:
1. Example: H2 + Br2 has order 3/2.

Question 19: Activation energy (Ea) and rate constants (k1 and k2) of a reaction at two different temperatures (T1 and T2) are related by
(a) \( \ln\dfrac{k_2}{k_1} = -\dfrac{E_a}{R}\left(\dfrac1{T_2}+\dfrac1{T_1}\right) \)
(b) \( \ln\dfrac{k_2}{k_1} = \dfrac{E_a}{R}\left(\dfrac1{T_1}-\dfrac1{T_2}\right) \)
(c) \( \ln\dfrac{k_2}{k_1} = -\dfrac{E_a}{R}\left(\dfrac1{T_1}-\dfrac1{T_2}\right) \)
(d) \( \ln\dfrac{k_2}{k_1} = -\dfrac{E_a}{R}\left(\dfrac1{T_2}-\dfrac1{T_1}\right) \)
Show Answer & Explanation

Answer: (b) \( \ln\dfrac{k_2}{k_1} = \dfrac{E_a}{R}\left(\dfrac1{T_1}-\dfrac1{T_2}\right) \)

Explanation:
1. ln k = ln A − Ea/RT, so ln k2 − ln k1 = −(Ea/R)(1/T2 − 1/T1).
2. This equals (Ea/R)(1/T1 − 1/T2).

Teacher's Note:
1. If T2 > T1, then 1/T1 − 1/T2 > 0 and k2 > k1.
2. Check the sign using this logic.

Question 20: A reaction having equal energies of activation for forward and reverse reactions has
(a) ΔH = ΔG = ΔS = 0
(b) ΔS = 0
(c) ΔG = 0
(d) ΔH = 0
Show Answer & Explanation

Answer: (d) ΔH = 0

Explanation:
1. ΔH = Ea(forward) − Ea(reverse) = 0.

Teacher's Note:
1. Equal activation energies means ΔH is zero; nothing is implied for ΔG or ΔS.

Question 21: What is the activation energy of a reaction if its rate doubles when the temperature is raised from 20°C to 35°C? (R = 8.314 J mol−1 K−1)
(a) 15.1 kJ mol−1
(b) 342 kJ mol−1
(c) 269 kJ mol−1
(d) 34.7 kJ mol−1
Show Answer & Explanation

Answer: (d) 34.7 kJ mol−1

Explanation:
1. \( \log 2 = \dfrac{E_a}{2.303R}\cdot\dfrac{T_2-T_1}{T_1T_2} \), T1 = 293 K, T2 = 308 K.
2. Ea = 2.303 × 8.314 × 0.3010 × (293 × 308)/15 = 34.7 × 103 J mol−1.

Teacher's Note:
1. Convert °C to K before using the Arrhenius equation.

Question 22: The activation energy of the forward reaction of an endothermic process is 50 kJ and the enthalpy change is 20 kJ. The activation energy for the backward reaction is
(a) 30 kJ
(b) 20 kJ
(c) 70 kJ
(d) 50 kJ
Show Answer & Explanation

Answer: (a) 30 kJ

Explanation:
1. ΔH = Ea(f) − Ea(b).
2. Ea(b) = 50 − 20 = 30 kJ.

Teacher's Note:
1. Backward barrier is lower in an endothermic reaction.

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Multiple Choice Questions (MCQs) for JEE Chemistry Chemical Kinetics

Download Multiple Choice Questions: Chemical Kinetics (JEE Chemistry)

Review structured objective questions for JEE Chemistry Chemical Kinetics. Built according to official JEE guidelines, these MCQ sets support daily revision and core concept reinforcement.

Concept Clarification for Chemical Kinetics

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