Chemical Kinetics: Class 12 Previous Year Questions

Chemical Kinetics questions asked in CBSE board exams

Repeated questions first. Open the free app to see each question as it appeared in the paper, with its marking scheme.

1. A first order reaction is 50% complete in 30 minutes at 300 K and in 10 minutes at 320 K. Calculate activation energy (Ea) for the reaction. [R = 8.314 J K–1 mol–1] 3 [Given : log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021] 16 29. F – CH2 – COOH (  …
   Board 20233 marksshort answerRepeated: 2022,2023,2025
2. A certain reaction is 50% complete in 20 minutes at 300 K and the same reaction is 50% complete in 5 minutes at 350 K. Calculate the activation energy if it is a first order reaction. [R = 8.314 J K-1 mol-1; log 4 = 0.602]
   Board 20253 marksshort answerRepeated: 2023,2025
3. A first order reaction is 50% complete in 40 minutes. Calculate the time required for the completion of 90% of reaction. [Given : log 2 = 0.3010, log 10 = 1]
   Board 20221 markvery shortRepeated: 2022,2023
4. For the first order thermal decomposition reaction, following data was obtained : 3 C2H5Cl(g) — C2H4(g) + HCl(g) S. No. Time(s) Total Pressure (atm) 1 0 0.30 2 30 0.50 Calculate rate constant. [Given : log 3 = 0.48]
   Board 20263 marksshort answer
5. (A) The concentration of the reactant is reduced from 0.6 mol L–1 to 0.2 mol L–1 in 5 minutes in a first order reaction. Calculate rate constant of the reaction. (log 3 = 0.48) 2 OR (B) Rate constant k for the first order reaction is 2.54  10–3 s–1. Calculate…
   Board 20262 marksshort answer
6. (a) Define activation energy. 1 + 1 (b) Write the unit of rate constant for (i) zero order reaction, (ii) second order reaction.
   Board 20262 marksshort answer
7. Which of the following curve represents the first order reaction ? 1 (A) (B) (C) (D)
   Board 20261 markMCQ
8. The order for the given reaction is : 1 A + 2B  Products Rate = k[A]½ [B]1 (A) 1.5 (B) 1 (C) 0.5 (D)
   Board 20261 markMCQ
9. Identify the correct increasing order of boiling points of the given compounds : 1 (A) Propan–1– ol < butan–1–ol < butan –2–ol < pentan–1–ol (B) Pentan–1– ol < butan–1–ol < butan –2–ol < Propan–1–ol (C) Propan–1– ol < butan–2–ol < butan –1–ol < pentan–1–ol (D)…
   Board 20261 markMCQ
10. Following reaction takes place in one step : 2 2A + B — 2C How will the rate of above reaction change if the volume of the reaction vessel is decreased to one third of its original volume ? Will there be any change in the order of reaction with the reduced vo…
    Board 20262 marksshort answer
11. Identify the correct statement : 1 (A) Molecularity of a reaction is an experimental quantity. (B) For complex reactions molecularity has no meaning. (C) Molecularity of a reaction can be zero or even a fraction. (D) Molecularity more than three is very common…
    Board 20261 markMCQ
12. Assertion (A) : The molecularity of the given reaction is 2 1 2HI –– H2 + I2 Reason (R) : Two molecules of the reactants are involved in simultaneous collision between them.
    Board 20261 markAssertion-Reason
13. 1 Define the following terms : 2×1 (a) Pseudo first order reaction (b) Half-life period of reaction (t1/2)
    Board 20252 marksshort answer
14. Which among the following is a false statement ? (A) Rate of zero order reaction is independent of initial concentration of reactant. (B) Half-life of a zero order reaction is inversely proportional to the rate constant. (C) Molecularity of a reaction may be z…
    Board 20251 markMCQ
15. (A) The rate constant for a zero order reaction A · P is 0.0030 mol L-ls-1. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075 M ? OR (B) The decomposition of NH, on platinum surface is zero order reaction. What are the rates…
    Board 20252 marksshort answer
16. Arrange the following compounds in increasing order of their boiling points : CH3 CH: (i) CH- CH,Br (ii) CH,CH,CH,CH,Br (i) H,C-C- CH CH3 Br The correct order is (A) (I) > () > (I) (B) (III) >(II) >(T) (C) (II) > () > (III) (t) > () > (III) () 7. (A)RTR (B) (C…
    Board 20251 markMCQ
17. Which is the correct order of acid strength from the following ? C,H,OH >H,O > ROH (A) (B) C,H,OH>ROH>H,O (C)I ROH > C,H,OH >H,0 (D) H,O >C,H,OH>ROH
    Board 20251 markMCQ
18. The number of molecules that react with each other in an elementary reactionisameasureofthe: (A) activation energy of the reaction (B) stoichiometry of the reaction (C) molecularity of the reaction (D) order of the reaction
    Board 20251 markMCQ
19. Assertion (A) : In a first order reaction, if the concentration of the reactant is doubled, its half-life is also doubled. Reason (R) : The half-life of a reaction does not depend upon the initial concentration of the reactant in a first order reaction.
    Board 20251 markAssertion-Reason
20. The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, tempe…
    Board 20254 marksshort answer

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