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Chemical Kinetics

JEE Main 2025 (Online) 3rd April Morning ShiftMCQMedium📈 Topic in 17% papers+4−1
Ques. 1JEE Main 2025, 3 April (Morning Shift)

In a reaction A + B C, initial concentrations of A and B are related as [A]0 = 8[B]0. The half-lives of A and B are 10 min and 40 min, respectively. If they start to disappear at the same time, both following first order kinetics, after how much time will the concentration of both the reactants be same?

  1. 20 min
  2. 40 min
  3. 80 min
  4. 60 min

Answer

(2) 40 min

Solution

For first order, [A] = [A]0 e-kA t and [B] = [B]0 e-kB t, with k = 0.693t1/2, so

kA = 210 min-1 and kB = 240 min-1.

For [A] = [B]: 8[B]0 e-kA t = [B]0 e-kB t

8 = (kA - kB) t

3 2 = 2 ( 110 - 140 ) t = 3 240 t

t = 40 min

Check: in 40 min A passes 4 half-lives, so [A] = 8[B]016 = [B]02, while B passes 1 half-life, so [B] = [B]02 ✓

Answer: (2)

Keep practising — Chemical Kinetics

Ques. 2JEE Main 2025, 3 April (Evening Shift)

Consider the following statements related to temperature dependence of rate constants. Identify the correct statements. Choose the correct answer from the options given below:

  1. A, C and D Only
  2. B, D and E Only
  3. B and C Only
  4. A and B Only
Ques. 3JEE Main 2025, 2 April (Morning Shift)

For the reaction A products. [figure] The concentration of A at 10 minutes is 10-3 mol L-1 (nearest integer). The reaction was started with 2.5 mol L-1 of A.

Ques. 4JEE Main 2025, 2 April (Evening Shift)

Reactant A converts to product D through the given mechanism (with the net evolution of heat): A B slow; H = +ve B C fast; H = -ve C D fast; H = -ve Which of the following represents the above reaction mechanism?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 5JEE Main 2025, 2 April (Evening Shift)

For the reaction A B the following graph was obtained. The time required (in seconds) for the concentration of A to reduce to 2.5 g L-1 (if the initial concentration of A was 50 g L-1) is . (Nearest integer) Given : 2 = 0.3010 [figure]

Ques. 6JEE Main 2025, 29 January (Morning Shift)

The reaction A2 + B2 2AB follows the mechanism: A2 k-1 k1 A + A (fast) A + B2 k2 AB + B (slow) A + B AB (fast) The overall order of the reaction is:

  1. 3
  2. 2.5
  3. 1.5
  4. 2
Ques. 7JEE Main 2025, 29 January (Evening Shift)

Drug X becomes ineffective after 50\% decomposition. The original concentration of drug in a bottle was 16 mg/mL which becomes 4 mg/mL in 12 months. The expiry time of the drug in months is . Assume that the decomposition of the drug follows first order kinetics.

  1. 12
  2. 3
  3. 6
  4. 2
Ques. 8JEE Main 2025, 28 January (Morning Shift)

array|c|c| [A]0/ mol L-1 & t1/2/min \ 0.100 & 200 \ 0.025 & 100 \ array For a given reaction R P, t1/2 is related to [A]0 as given in table. Given: 2 = 0.30 Which of the following is true? Choose the correct answer from the options given below:

  1. A and C Only
  2. A, B and D Only
  3. A and B Only
  4. C and D Only
Ques. 9JEE Main 2025, 28 January (Evening Shift)

Consider an elementary reaction A(g) + B(g) C(g) + D(g) If the volume of reaction mixture is suddenly reduced to 13 of its initial volume, the reaction rate will become 'x' times of the original reaction rate. The value of x is :

  1. 3
  2. 9
  3. 13
  4. 19
Ques. 10JEE Main 2025, 28 January (Evening Shift)

For bacterial growth in a cell culture, growth law is very similar to the law of radioactive decay. Which of the following graphs is most suitable to represent bacterial colony growth? Where N - Number of bacteria at any time, N0 - Initial number of bacteria.

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 11JEE Main 2025, 24 January (Morning Shift)

For a reaction, N2O5(g) 2NO2(g) + 12O2(g) in a constant volume container, no products were present initially. The final pressure of the system when 50\% of reaction gets completed is

  1. 5/2 times of initial pressure
  2. 7/2 times of initial pressure
  3. 7/4 times of initial pressure
  4. 5 times of initial pressure

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