Kerala Plus Two Chemistry Chapter 3: Chemical Kinetics Important Questions

Chemical Kinetics is a scoring unit in the board syllabus. The board exam includes conceptual questions and numerical problems from this chapter. Students must master rate expressions, collision theory, and temperature dependence. Checking the Kerala Class 12 Syllabus shows the high weightage given to this topic. Practising these problems prepares students for competitive exams as well.

Kerala Plus Two Chemistry Chapter 3 Most Important Questions cover key definitions, derivations, and numerical problems from Chapter 3. The Kerala Plus Two Exam Pattern provides details about the exam structure and marking scheme.

Kerala Plus Two Chemistry Chapter 3 Chemical Kinetics Most Important Questions

Kerala Plus Two Chemistry Chemical Kinetics Important Questions Class 12 cover key concepts, definitions, derivations, and numerical problems from Chapter 3. These questions focus on reaction rates, rate laws, half-life, and the Arrhenius equation.

1. What is meant by the order of a reaction? How does it differ from the molecularity of a reaction?

Order is the sum of the powers of the concentration terms in the experimental rate law. Molecularity is the total number of reacting species colliding simultaneously in an elementary reaction. Order can be zero or fractional, while molecularity must be an integer of 1 or greater.

2. For the reaction 2NO(g) + O₂(g) → 2NO₂(g), the rate law is given as Rate = k[NO]²[O₂]. Determine the overall order and the molecularity of the reaction.

Overall order = 2 + 1 = 3. Molecularity = 3.

3. The conversion of molecule A to B follows second-order kinetics. If the concentration of A is increased to three times, how will it affect the rate of formation of B?

For second-order kinetics, Rate = k[A]². If [A] becomes 3[A], the new rate is k(3[A])² = 9k[A]². The rate of formation of B increases by 9 times.

4. State the units of the rate constant (k) for zero, first, and second-order reactions if the concentration is expressed in mol L⁻¹ and time is in seconds.

• Zero-order: mol L⁻¹ s⁻¹

• First-order: s⁻¹

• Second-order: mol⁻¹ L s⁻¹

5. Define the half-life period of a reaction. Derive an expression to show that the half-life of a first-order reaction is independent of the initial concentration.

Half-life is the time taken for the concentration of a reactant to reduce to half its initial value.

Derivation: k = (2.303 / t) log([R]₀ / [R]). When t = t½, [R] = [R]₀ / 2. Substituting these gives t½ = (2.303 / k) log 2 = 0.693 / k. Since [R]₀ does not appear in the final equation, it is independent of the initial concentration.

6. A first-order reaction has a rate constant of 1.15 × 10⁻³ s⁻¹. How long will it take for 5 g of the reactant to reduce to 3 g?

Given: k = 1.15 × 10⁻³ s⁻¹, [R]₀ = 5 g, [R] = 3 g

t = (2.303 / k) log([R]₀ / [R])
t = (2.303 / 1.15 × 10⁻³) × log(5/3)
t = 444.3 seconds

7. An archaeological substance containing wood had only 66.66% of the ¹⁴C found in a living tree. Calculate the age of the sample if the half-life of ¹⁴C is 5730 years.

Given: t½ = 5730 years

k = 0.693 / 5730 = 1.21 × 10⁻⁴ yr⁻¹

t = (2.303 / k) log([R]₀ / [R]), where [R]₀ = 100 and [R] = 66.66
t = (2.303 / 1.21 × 10⁻⁴) × log(100 / 66.66)
t = 3352.4 years

8. Explain the effect of temperature on the rate of a chemical reaction. Mention the Arrhenius equation and explain the terms involved.

As temperature increases, the kinetic energy of molecules increases, leading to more effective collisions and an increased reaction rate.

Arrhenius equation: k = A e^(−Ea/RT)

Here, k is the rate constant, A is the Arrhenius pre-exponential factor, Ea is the activation energy, R is the universal gas constant, and T is the absolute temperature.

9. The rate of a reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.

Given: T₁ = 293 K, T₂ = 313 K, k₂ = 4k₁

log(k₂/k₁) = (Ea / 2.303R) × [(T₂ − T₁) / (T₁T₂)]
log 4 = (Ea / (2.303 × 8.314)) × [20 / (293 × 313)]
Ea = 52,854 J mol⁻¹ or 52.85 kJ mol⁻¹

10. Explain how the presence of a catalyst affects the rate of a chemical reaction.

A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy barrier. This allows a greater fraction of reactant molecules to successfully convert into products without the catalyst being permanently consumed.

Kerala Plus Two Chemistry Chapter 3 Chemical Kinetics PDF Download

The Kerala Plus Two Chemistry Chapter 3 MIQs PDF includes important Chemical Kinetics questions with detailed solutions for offline practice and revision. Refer to the Kerala Plus Two Time Table for exam dates and preparation planning.

How to Use Important Solutions for Kerala Class 12 Chemistry Chemical Kinetics for Exam Preparation

Consistent practice ensures better retention and clarity. Follow these organised steps to prepare using the Kerala Plus Two Chemistry Chapter 3 Important Questions:

• Review Core Concepts: Read textbook theory before solving problems. Understand definitions of Rate Constant, Activation Energy, and Pseudo First Order Reaction thoroughly.

• Practice Numerical Problems: Solve rate constant and half-life calculations step by step. This builds speed and minimises calculation errors.

• Check Marking Criteria: Review the Kerala Plus Two Grading and Marking system. Write answers matching the required step-wise format.

• Identify Weak Areas: Note difficult questions and revisit the textbook. Clear doubts immediately using Kerala Class 12 Chemistry Chemical Kinetics Important Questions to avoid confusion during exams.

• Revisit Formulas Regularly: Maintain a concise formula sheet for quick daily revisions. This aids quick recall of units and graphs.

Practising these Kerala Plus Two Chemistry Chemical Kinetics important questions can help students strengthen key concepts, improve numerical problem-solving skills, and prepare effectively for the board exam. Download the PDF and revise important formulas, derivations, and reactions regularly.