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Chemical Kinetics MCQs

Class 12 Chemistry — questions with answers and worked explanations.

20 free questions Class 12 Chemistry Answers + explanations No sign-up

These questions are drawn from the Pariksha Sutra question bank for Chemical Kinetics, part of the Class 12 Chemistry syllabus. Each one shows the correct answer and, where a method helps, the working behind it.

Read the question, decide your answer before looking, then check the explanation — that is what turns practice into marks. If a question catches you out, the explanation is the part worth re-reading.

Questions

Question 1
The rate of a chemical reaction is best defined as the change in:
  1. temperature per unit time
  2. mass of reactant per unit volume
  3. pressure per unit mole
  4. concentration of reactant or product per unit time
Answer: concentration of reactant or product per unit time
Question 2
Which statement about molecularity is correct?
  1. It can be zero
  2. It cannot be zero or fractional
  3. It can be fractional
  4. It is always equal to order
Answer: It cannot be zero or fractional
Question 3
For a first order reaction, a plot of ln[A] versus time gives a straight line with slope equal to:
  1. -2.303k
  2. -k
  3. k/2.303
  4. +k
Answer: -k
Question 4
For a zero order reaction, the half-life is:
  1. inversely proportional to initial concentration
  2. proportional to log of concentration
  3. independent of initial concentration
  4. directly proportional to initial concentration
Answer: directly proportional to initial concentration
Question 5
For many reactions near room temperature, a rise of 10 degrees in temperature approximately changes the rate by a factor of:
  1. 2 to 3
  2. 100
  3. 1/2
  4. 10
Answer: 2 to 3
Question 6
Molecularity of an elementary reaction is:
  1. the number of reacting species colliding in an elementary step
  2. never greater than one
  3. equal to the order for complex reactions
  4. always experimentally determined
Answer: the number of reacting species colliding in an elementary step
Question 7
For a zero order reaction, the concentration of reactant at time t is given by:
  1. [A] = [A0] e^(-kt)
  2. [A] = [A0] - kt
  3. ln[A] = ln[A0] - kt
  4. [A] = [A0]/(1+kt)
Answer: [A] = [A0] - kt
Question 8
For a zero order reaction, the half-life is given by:
  1. 1/k[A0]
  2. [A0]/2k
  3. 2k/[A0]
  4. 0.693/k
Answer: [A0]/2k
Question 9
The two-temperature form of the Arrhenius equation relating k1 and k2 is:
  1. log(k2/k1) = (2.303R/Ea)(1/T1 - 1/T2)
  2. log(k1/k2) = (Ea/2.303R)(1/T1 - 1/T2)
  3. log(k2/k1) = (Ea/2.303R)(1/T2 - 1/T1)
  4. log(k2/k1) = (Ea/2.303R)(1/T1 - 1/T2)
Answer: log(k2/k1) = (Ea/2.303R)(1/T1 - 1/T2)
Question 10
According to collision theory, the rate of a bimolecular reaction is proportional to:
  1. Z e^(Ea/RT)
  2. Z / Ea
  3. e^(RT/Ea)
  4. Z e^(-Ea/RT)
Answer: Z e^(-Ea/RT)
Question 11
For the reaction N2 + 3H2 -> 2NH3, the rate of disappearance of H2 is related to rate of appearance of NH3 as:
  1. -d[H2]/dt = d[NH3]/dt
  2. -d[H2]/dt = (3/2) d[NH3]/dt
  3. -d[H2]/dt = (2/3) d[NH3]/dt
  4. -d[H2]/dt = 3 d[NH3]/dt
Answer: -d[H2]/dt = (3/2) d[NH3]/dt
Question 12
The units of the rate constant for a first order reaction are:
  1. L^2/mol^2/s
  2. mol/L/s
  3. L/mol/s
  4. s^-1
Answer: s^-1
Question 13
For a first order reaction, a plot of log([A0]/[A]) versus time is a straight line with slope:
  1. k
  2. 2.303k
  3. -k
  4. k/2.303
Answer: k/2.303
Question 14
After 3 half-lives, the fraction of a first order reactant remaining is:
  1. 1/4
  2. 1/2
  3. 1/16
  4. 1/8
Answer: 1/8
Question 15
Activation energy of a reaction is the:
  1. minimum extra energy reactants must gain to react
  2. energy of the products
  3. energy released in the reaction
  4. total energy of the reactants
Answer: minimum extra energy reactants must gain to react
Question 16
Which factor generally does NOT affect the rate of a chemical reaction?
  1. Total time the reaction is allowed to run
  2. Presence of a catalyst
  3. Concentration of reactants
  4. Temperature
Answer: Total time the reaction is allowed to run
Question 17
The units of the rate constant for a zero order reaction are:
  1. mol/L/s
  2. L/mol/s
  3. s^-1
  4. L^2/mol^2/s
Answer: mol/L/s
Question 18
For a zero order reaction, which plot gives a straight line?
  1. [A] vs t
  2. ln[A] vs t
  3. 1/[A] vs t
  4. log[A] vs t
Answer: [A] vs t
Question 19
A radioactive first order decay has a half-life of 10 years. The fraction remaining after 40 years is:
  1. 1/32
  2. 1/16
  3. 1/8
  4. 1/4
Answer: 1/16
Question 20
A reaction with a lower activation energy will generally have a:
  1. higher enthalpy
  2. zero rate constant
  3. faster rate
  4. slower rate
Answer: faster rate

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