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Chemical Kinetics · Question 36

JEE Main 2025 (Online) 3rd April Morning ShiftMCQMedium📈 Topic in 23% papers+4−1
1

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

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

kA = 210 min-1, 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, [A] = 8[B]016 = [B]02; B passes 1 half-life, [B] = [B]02 ✓

Answer: (2)

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Keep practising — Chemical Kinetics

2

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
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3

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.

JEE Main 2025 (Online) 2nd April Morning Shift
4

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]
JEE Main 2025 (Online) 2nd April Evening Shift
5

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]

JEE Main 2025 (Online) 2nd April Evening Shift
6

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
JEE Main 2025 (Online) 29th January Morning Shift
7

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
JEE Main 2025 (Online) 28th January Morning Shift
8

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
JEE Main 2025 (Online) 28th January Evening Shift
9

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]
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