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Chemical Kinetics · Question 18

JEE Main 2026 (Online) 24th January Evening ShiftNumericalEasy📈 Topic in 23% papers+4
1

The half-life of 65Zn is 245 days. After x days, 75\% of original activity remained. The value of x in days is . (Nearest integer) (Given: 3 = 0.4771 and 2 = 0.3010)

Answer

102

Solution

Radioactive decay follows first-order kinetics: t = 2.303k A0A and k = 0.693t1/2 = 2.303 2t1/2

⇒ x = t1/2 (A0/A) 2

Here A0A = 10075 = 43, so 43 = 2 2 - 3 = 0.6020 - 0.4771 = 0.1249

⇒ x = 245 0.12490.3010

= 101.7 days 102 days

Answer: 102

JEE Main 2026 (Online) 24th January Evening Shift

Keep practising — Chemical Kinetics

2

For the thermal decomposition of reactant AB(g), the following plot is constructed. [figure] The half-life of the reaction is 'x' min. x = min. (Nearest integer)

JEE Main 2026 (Online) 23rd January Morning Shift
3

[figure] Given above is the concentration vs time plot for a dissociation reaction : A nB. Based on the data of the initial phase of the reaction (initial 10 min), the value of n is .

  1. 2
  2. 5
  3. 4
  4. 3
JEE Main 2026 (Online) 23rd January Evening Shift
4

Observe the following reactions at T(K). I. A products. II. 5Br-(aq) + BrO3-(aq) + 6H+(aq) 3Br2(aq) + 3H2O(l) Both the reactions are started at 10.00 am. The rates of these reactions at 10.10 am are same. The value of - [Br-] t at 10.10 am is 2 10-4 mol L-1 min-1. The concentration of A at 10.10 am is 10-2 mol L-1. What is the first order rate constant (in min-1) of reaction I?

  1. 4 10-3
  2. 2 10-3
  3. 10-3
  4. 10-2
JEE Main 2026 (Online) 23rd January Evening Shift
5

A product (First order reaction). Three sets of experiments were performed for a reaction under similar experimental conditions: Run 1 100 mL of 10 M solution of reactant A Run 2 200 mL of 10 M solution of reactant A Run 3 100 mL of 10 M solution of reactant A + 100 mL of H2O added. The correct variation of rate of reaction is

  1. Run 1 = Run 2 = Run 3
  2. Run 3 < Run 1 < Run 2
  3. Run 1 < Run 2 < Run 3
  4. Run 3 < Run 1 = Run 2
JEE Main 2026 (Online) 22nd January Morning Shift
6

The temperature at which the rate constants of the given below two gaseous reactions become equal is K. (Nearest integer) X Y, k1 = 106 e -30000T P Q, k2 = 104 e -24000T Given : 10 = 2.303

JEE Main 2026 (Online) 22nd January Morning Shift
7

Correct statements regarding Arrhenius equation among the following are : Choose the correct answer from the options given below :

  1. A and B Only
  2. B and D Only
  3. B and C Only
  4. A and C Only
JEE Main 2026 (Online) 22nd January Evening Shift
8

Consider A k1 B and C k2 D are two reactions. If the rate constant (k1) of the A B reaction can be expressed by the following equation 10 k = 14.34 - 1.5 104T/K and activation energy of C D reaction (Ea2) is 15th of the A B reaction (Ea1), then the value of (Ea2) is kJ mol-1. (Nearest Integer)

JEE Main 2026 (Online) 22nd January Evening Shift
9

Pre-exponential factors of two different reactions of same order are identical. Let activation energy of first reaction exceed the activation energy of second reaction by 20 kJ mol-1. If k1 and k2 are the rate constants of first and second reaction respectively at 300 K, then k2k1 will be . (nearest integer) [R = 8.3 J K-1 mol-1]

JEE Main 2026 (Online) 21st January Morning Shift
10

Decomposition of A is a first order reaction at T(K) and is given by A(g) B(g) + C(g). In a closed 1 L vessel, 1 bar A(g) is allowed to decompose at T(K). After 100 minutes, the total pressure was 1.5 bar. What is the rate constant (in min-1) of the reaction? ( 2 = 0.3)

  1. 6.9 10-4
  2. 6.9 10-3
  3. 6.9 10-1
  4. 6.9 10-2
JEE Main 2026 (Online) 21st January Evening Shift
11

In a first order decomposition reaction, the time taken for the decomposition of reactant to one fourth and one eighth of its initial concentration are t1 and t2 (s), respectively. The ratio t1/t2 will be:

  1. 43
  2. 32
  3. 34
  4. 23
JEE Main 2025 (Online) 8th April Evening Shift

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