MCQs on Chemical Kinetics – Class 12 Chemistry

Physical Chemistry – MCQ Titles (NCERT Based)
Course: CBSE Class 12 Chemistry – MCQs with Answers and Explanations

The following 50 NCERT-based MCQs are carefully structured to cover all key concepts of the Chemical Kinetics chapter as prescribed by CBSE. Questions are organized section-wise and include theory, numericals, graphs, and application-based MCQs, making them ideal for CBSE Class 12 board exams.

Section A: Introduction to Chemical Kinetics

1. Chemical kinetics deals with:

A. Energy changes in reactions
B. Rate of chemical reactions
C. Equilibrium of reactions
D. Atomic structure

Correct Answer: B
Explanation: Chemical kinetics is the study of reaction rates and factors affecting them.

2. The rate of a reaction is defined as:

A. Change in concentration per unit time
B. Change in pressure per unit time
C. Change in temperature per unit time
D. Change in volume per unit time

Correct Answer: A
Explanation: Rate = change in concentration of reactant or product per unit time.

3. Unit of rate of reaction is:

A. mol L⁻¹
B. mol L⁻¹ s⁻¹
C. s⁻¹
D. L mol⁻¹ s⁻¹

Correct Answer: B
Explanation: Rate involves concentration change per unit time.

4. Average rate of reaction is calculated over:

A. An instant
B. Total reaction time
C. A small time interval
D. Equilibrium stage

Correct Answer: C
Explanation: Average rate is measured over a finite time interval.

5. Instantaneous rate is equal to:

A. Average rate
B. Slope of tangent on concentration–time graph
C. Slope of chord
D. Zero

Correct Answer: B
Explanation: Instantaneous rate is the slope of tangent at a given point.

Section B: Rate Law and Order of Reaction

6. Rate law expresses rate as a function of:

A. Temperature
B. Pressure
C. Concentration of reactants
D. Volume

Correct Answer: C
Explanation: Rate law relates reaction rate to reactant concentrations.

7. Order of reaction is:

A. Sum of coefficients of reactants
B. Sum of powers of concentration terms
C. Always an integer
D. Equal to molecularity

Correct Answer: B
Explanation: Order is determined experimentally from rate law.

8. Order of reaction can be:

A. Only whole number
B. Only fractional
C. Zero, fractional or integral
D. Only positive

Correct Answer: C
Explanation: Order may be zero, fractional, or whole number.

9. A zero-order reaction has rate:

A. Proportional to concentration
B. Inversely proportional to concentration
C. Independent of concentration
D. Always zero

Correct Answer: C
Explanation: Rate = k for zero-order reactions.

10. For a first-order reaction, unit of rate constant is:

A. mol L⁻¹ s⁻¹
B. L mol⁻¹ s⁻¹
C. s⁻¹
D. mol⁻¹ s⁻¹

Correct Answer: C
Explanation: First-order rate constant has unit s⁻¹.

Section C: Molecularity and Mechanism

11. Molecularity refers to:

A. Overall reaction
B. Rate law
C. Number of molecules in elementary step
D. Stoichiometry

Correct Answer: C
Explanation: Molecularity applies only to elementary reactions.

12. Molecularity is always:

A. Fractional
B. Zero
C. Whole number
D. Negative

Correct Answer: C
Explanation: It represents actual colliding species.

13. Reaction mechanism is:

A. Balanced chemical equation
B. Sequence of elementary steps
C. Rate law
D. Equilibrium expression

Correct Answer: B
Explanation: Complex reactions occur via multiple steps.

14. Rate-determining step is:

A. Fastest step
B. Slowest step
C. Final step
D. Initial step

Correct Answer: B
Explanation: Slowest step controls overall rate.

15. Molecularity of a bimolecular reaction is:

A. 1
B. 2
C. 3
D. 0

Correct Answer: B
Explanation: Two reacting species are involved.

Section D: Integrated Rate Equations

16. Integrated rate equation relates:

A. Rate and temperature
B. Concentration and time
C. Rate and pressure
D. Energy and rate

Correct Answer: B
Explanation: It gives concentration variation with time.

17. Half-life of a first-order reaction is:

A. Dependent on initial concentration
B. Independent of initial concentration
C. Zero
D. Infinite

Correct Answer: B
Explanation: t₁/₂ = 0.693/k.

18. Half-life of zero-order reaction depends on:

A. Rate constant only
B. Initial concentration
C. Temperature only
D. Pressure

Correct Answer: B
Explanation: t₁/₂ ∝ initial concentration.

19. A plot of log[A] vs time for first-order reaction is:

A. Curved
B. Horizontal
C. Straight line
D. Parabolic

Correct Answer: C
Explanation: Linear plot confirms first-order reaction.

20. Unit of rate constant for second-order reaction is:

A. s⁻¹
B. mol L⁻¹ s⁻¹
C. L mol⁻¹ s⁻¹
D. L² mol⁻² s⁻¹

Correct Answer: C
Explanation: Second-order rate constant unit is L mol⁻¹ s⁻¹.

Section E: Factors Affecting Rate of Reaction

21. Increase in temperature generally:

A. Decreases reaction rate
B. Has no effect
C. Increases reaction rate
D. Stops reaction

Correct Answer: C
Explanation: Higher temperature increases molecular collisions.

22. Effect of catalyst is to:

A. Increase ΔH
B. Lower activation energy
C. Change equilibrium constant
D. Increase activation energy

Correct Answer: B
Explanation: Catalyst provides alternative lower-energy pathway.

23. Rate of reaction increases with:

A. Decrease in surface area
B. Increase in surface area
C. Increase in pressure only
D. Decrease in concentration

Correct Answer: B
Explanation: More surface area means more collisions.

24. Rate of gaseous reaction increases with:

A. Decrease in pressure
B. Increase in pressure
C. Decrease in volume
D. Both B and C

Correct Answer: D
Explanation: Higher pressure or lower volume increases collision frequency.

25. Nature of reactants affects rate because of:

A. Color
B. Physical state
C. Chemical bond strength
D. Density

Correct Answer: C
Explanation: Stronger bonds require more energy to break.

Section F: Arrhenius Equation and Activation Energy

26. Arrhenius equation is:

A. k = A + e⁻ᴱᵃ/ᴿᵀ
B. k = A e⁻ᴱᵃ/ᴿᵀ
C. k = Ea/RT
D. k = RT/Ea

Correct Answer: B
Explanation: It relates rate constant with temperature.

27. Activation energy is:

A. Energy released during reaction
B. Minimum energy required to start reaction
C. Energy of products
D. Energy of reactants

Correct Answer: B
Explanation: Reactants must overcome activation energy barrier.

28. Lower activation energy means:

A. Slower reaction
B. Faster reaction
C. No reaction
D. Equilibrium

Correct Answer: B
Explanation: Easier formation of activated complex.

29. Catalyst affects activation energy by:

A. Increasing it
B. Eliminating it
C. Lowering it
D. Keeping it constant

Correct Answer: C
Explanation: Catalyst reduces energy barrier.

30. Arrhenius plot is between:

A. k vs T
B. log k vs 1/T
C. Ea vs T
D. log k vs T

Correct Answer: B
Explanation: Linear plot gives activation energy.

Section G: Collision Theory

31. According to collision theory, reaction occurs when:

A. Molecules collide
B. Molecules collide with proper energy and orientation
C. Temperature is high
D. Pressure is high

Correct Answer: B
Explanation: Only effective collisions cause reactions.

32. Activated complex is:

A. Stable molecule
B. Intermediate with maximum energy
C. Product
D. Catalyst

Correct Answer: B
Explanation: It is unstable and short-lived.

33. Collision frequency increases with:

A. Decrease in temperature
B. Increase in temperature
C. Decrease in concentration
D. Catalyst

Correct Answer: B
Explanation: Higher temperature increases molecular speed.

34. Fraction of effective collisions increases with:

A. Decrease in activation energy
B. Decrease in temperature
C. Increase in pressure
D. Increase in volume

Correct Answer: A
Explanation: More molecules have sufficient energy.

35. Reaction rate depends directly on:

A. Total collisions
B. Effective collisions
C. Ineffective collisions
D. Molecular mass

Correct Answer: B
Explanation: Only effective collisions lead to reaction.

Section H: Exam-Oriented MCQs

36. Order and molecularity are equal for:

A. Complex reactions
B. Elementary reactions
C. Chain reactions
D. Catalytic reactions

Correct Answer: B
Explanation: For elementary reactions only.

37. Units of rate constant help in determining:

A. Molecularity
B. Order of reaction
C. Activation energy
D. Equilibrium constant

Correct Answer: B
Explanation: Order determines unit of k.

38. Which reaction has constant half-life?

A. Zero order
B. First order
C. Second order
D. Third order

Correct Answer: B
Explanation: Half-life of first-order reaction is constant.

39. Increasing concentration affects rate of:

A. Zero-order reaction
B. First-order reaction
C. Catalytic reaction
D. Photochemical reaction

Correct Answer: B
Explanation: Rate depends on concentration.

40. Fast reactions are difficult to study because:

A. They are unstable
B. They complete in short time
C. They have low activation energy
D. They release heat

Correct Answer: B
Explanation: Time resolution is limited.

41. Which graph gives rate constant?

A. Concentration vs time
B. log k vs 1/T
C. Rate vs concentration
D. Pressure vs time

Correct Answer: B
Explanation: Arrhenius plot yields k and Ea.

42. Rate constant depends on:

A. Concentration
B. Pressure
C. Temperature
D. Volume

Correct Answer: C
Explanation: k varies with temperature.

43. Half-life of second-order reaction:

A. Constant
B. Independent of concentration
C. Depends on initial concentration
D. Zero

Correct Answer: C
Explanation: t₁/₂ ∝ 1/[A]₀.

44. Which reaction has units of k as L mol⁻¹ s⁻¹?

A. Zero order
B. First order
C. Second order
D. Third order

Correct Answer: C
Explanation: Characteristic of second-order reactions.

45. Rate constant increases with:

A. Increase in activation energy
B. Decrease in temperature
C. Increase in temperature
D. Increase in pressure

Correct Answer: C
Explanation: Higher temperature increases k.

46. Catalyst does not affect:

A. Rate of reaction
B. Activation energy
C. Equilibrium constant
D. Reaction pathway

Correct Answer: C
Explanation: Catalyst does not change equilibrium position.

47. A reaction with order zero will have rate:

A. Proportional to concentration
B. Inversely proportional to concentration
C. Independent of concentration
D. Always increasing

Correct Answer: C
Explanation: Rate = k.

48. Slope of Arrhenius plot gives:

A. R
B. Ea
C. –Ea/2.303R
D. A

Correct Answer: C
Explanation: Used to calculate activation energy.

49. Rate of reaction becomes zero when:

A. Reaction is complete
B. Activation energy is low
C. Temperature is high
D. Catalyst is added

Correct Answer: A
Explanation: No reactants remain.

50. Chemical kinetics helps in:

A. Predicting reaction feasibility
B. Studying reaction speed
C. Calculating equilibrium constant
D. Finding atomic mass

Correct Answer: B
Explanation: Kinetics focuses on rate, not feasibility.

✅ End of NCERT-Based MCQs on Chemical Kinetics – Class 12 Chemistry