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Chemical Kinetics WBCHSE Class 12 MCQ & Practice Questions

Practice Chemical Kinetics MCQs for WBCHSE Class 12 Chemistry with answers, explanations, chapter revision and related ChemNexa mock tests.

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Chemical Kinetics Revision Guide for WBCHSE Class 12 Chemistry

Chemical Kinetics explains how fast chemical reactions occur and how rate changes with concentration, temperature and catalysts. Exam questions often combine definitions with graphs, integrated rate equations and half-life relationships.

For WBCHSE Class 12 Chemistry, focus on distinguishing rate law from stoichiometric coefficients, identifying reaction order from experimental data, using integrated equations correctly and interpreting the Arrhenius equation.

Important Topics

  • Rate of reaction and rate law
  • Order and molecularity
  • Integrated rate equations
  • Half-life of zero and first order reactions
  • Arrhenius equation and activation energy
  • Catalysis and temperature dependence

Important Formulae & Relationships

  • Rate = k[A]^m[B]^n
  • First order: ln([A]0/[A]) = kt
  • First-order half-life: t1/2 = 0.693/k
  • Arrhenius: k = Ae^(−Ea/RT)
  • ln(k2/k1) = −Ea/R (1/T2 − 1/T1)

Use formulas only after checking the required units, sign convention and assumptions for the question.

What to practise in Chemical Kinetics

Concept Revision

Revise definitions, principles, equations, trends and core ideas from Chemical Kinetics before attempting MCQs.

Exam-style MCQs

Use chapter-focused multiple-choice practice to improve accuracy, recall and application for WBCHSE Class 12 Chemistry.

Performance Practice

Attempt ChemNexa tests, review results and return to weak areas for another round of targeted revision.

Top 20 Chemical Kinetics MCQs with Answers

These public questions are selected from the exact Chemical Kinetics chapter, screened for topic relevance and deduplicated so repeated versions of the same MCQ are not shown publicly. Use them for quick revision, then sign in to attempt the complete test experience with more questions, results and performance review.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

1. A pseudo-first-order reaction occurs when

  • A. Rate is independent of every concentration
  • B. Molecularity is zero
  • C. One reactant is present in large excess
  • D. All reactants are equimolar always
Answer: C
Explanation: A nearly constant excess concentration is absorbed into an apparent rate constant.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

2. Pseudo-first-order reaction-এর উদাহরণে এক reactant large excess-এ থাকলে কী হয়?

  • A. তার concentration প্রায় constant
  • B. তার order infinite
  • C. k zero
  • D. reaction stops
Answer: A
Explanation: Large excess reactant-এর concentration change negligible; তার term apparent rate constant-এর মধ্যে absorb হয়।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

3. For a first-order reaction, t1/2 equals

  • A. k/0.693
  • B. 0.693/k
  • C. [A]0/(2k)
  • D. 1/(k[A]0)
Answer: B
Explanation: First-order half-life is independent of initial concentration.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

4. The half-life of a first-order reaction is independent of

  • A. Initial concentration
  • B. Rate constant
  • C. Temperature through k
  • D. Reaction identity
Answer: A
Explanation: t1/2=0.693/k contains no concentration term.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

5. The unit of a first-order rate constant is

  • A. mol L^-1 s^-1
  • B. L mol^-1 s^-1
  • C. mol^-1 L s
  • D. s^-1
Answer: D
Explanation: For first order, k has dimensions of reciprocal time.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

6. A catalyst increases reaction rate primarily by

  • A. Providing an alternative pathway with lower activation energy
  • B. Increasing ΔH permanently
  • C. Changing equilibrium constant
  • D. Increasing product stability only
Answer: A
Explanation: A catalyst lowers the activation barrier.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

7. First-order rate constant-এর unit কী?

  • A. mol L⁻¹ s⁻¹
  • B. s⁻¹
  • C. L mol⁻¹ s⁻¹
  • D. mol² L⁻²
Answer: B
Explanation: First-order k-এর dimension time⁻¹, তাই s⁻¹।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

8. Second-order rate constant-এর unit সাধারণত কী?

  • A. s⁻¹
  • B. L mol⁻¹ s⁻¹
  • C. mol L⁻¹ s⁻¹
  • D. L² mol⁻²
Answer: B
Explanation: Rate=k[A]² হলে k = concentration⁻¹ time⁻¹ = L mol⁻¹ s⁻¹।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

9. First-order half-life কী?

  • A. [A]0/2k
  • B. 0.693/k
  • C. 1/k[A]0
  • D. 2k
Answer: B
Explanation: t1/2 = ln2/k = 0.693/k; initial concentration-independent।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

10. Order of reaction কী হতে পারে?

  • A. শুধু integer
  • B. zero, fractional বা integer
  • C. কখনও zero নয়
  • D. always molecularity
Answer: B
Explanation: Experimental rate law-এর concentration exponents-এর sum order; zero বা fractional-ও হতে পারে।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

11. Catalyst activation energy-কে কী করে?

  • A. বাড়ায়
  • B. কম alternative pathway দেয়
  • C. reaction enthalpy বদলায়
  • D. equilibrium constant বদলায়
Answer: B
Explanation: Catalyst lower-Ea pathway দেয়; thermodynamic ΔH/ΔG° ও equilibrium position বদলায় না।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

12. First-order reaction-এ 2 half-life পরে reactant কত থাকে?

  • A. 1/2
  • B. 1/4
  • C. 1/8
  • D. 3/4
Answer: B
Explanation: প্রতি half-life-এ concentration অর্ধেক: (1/2)^2=1/4।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

13. First-order reaction-এ 3 half-life পরে fraction remaining?

  • A. 1/3
  • B. 1/6
  • C. 1/8
  • D. 1/9
Answer: C
Explanation: (1/2)^3 = 1/8।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

14. Homogeneous catalysis-এ catalyst ও reactants কেমন phase-এ থাকে?

  • A. একই phase
  • B. সবসময় আলাদা phase
  • C. catalyst solid only
  • D. reactants gas only
Answer: A
Explanation: Homogeneous catalysis-এ catalyst ও reacting species একই phase-এ থাকে।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

15. Heterogeneous catalysis-এ catalyst ও reactants?

  • A. একই molecular formula
  • B. different phases
  • C. both always gases
  • D. both always liquids
Answer: B
Explanation: Heterogeneous catalysis-এ catalyst সাধারণত different phase-এ থাকে, reaction surface-এ ঘটে।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

16. Activation energy কমলে fixed T-তে k কী করে?

  • A. কমে
  • B. বাড়ে
  • C. শূন্য হয়
  • D. unchanged সবসময়
Answer: B
Explanation: Arrhenius factor exp(−Ea/RT); Ea কমলে exponent কম negative হয়ে k বাড়ে।

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

17. The rate law for a reaction is determined primarily by

  • A. Balanced equation alone
  • B. Molecular mass
  • C. Colour
  • D. Experiment
Answer: D
Explanation: Reaction orders must generally be obtained experimentally.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

18. For rate=k

  • A. m-n
  • B. k
  • C. m+n
  • D. m×n
Answer: C
Explanation: Overall reaction order is the sum of concentration exponents.

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

19. Half-life of a zero-order reaction is

  • A. [A]0/(2k)
  • B. 0.693/k
  • C. 1/(k[A]0)
  • D. 2k/[A]0
Answer: A
Explanation: Setting [A]t=[A]0/2 in the zero-order equation gives t1/2=[A]0/(2k).

WBCHSE Class 12 Chemistry · Chemical Kinetics · Very Hard

20. For a first-order reaction, rate is

  • A. k
  • B. k[A]^2
  • C. k/[A]
  • D. k[A]
Answer: D
Explanation: First-order rate is proportional to the first power of concentration.

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Chemical Kinetics Practice Tests

Chemical Kinetics Frequently Asked Questions

What is the most important distinction in Chemical Kinetics?

Do not confuse reaction order with stoichiometric coefficients. Reaction order is determined from the experimentally observed rate law.

Which kinetics formulas should I memorise?

Know the integrated zero- and first-order equations, half-life relations and the Arrhenius equation, but also understand the units and conditions under which each is valid.

How can I reduce mistakes in kinetics numericals?

Write the order first, choose the matching integrated equation, keep units consistent and check whether logarithms are natural or base-10.

Continue with another chapter to build connected concepts and strengthen your overall Chemistry preparation.

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