jee main chemistry important questions | Chemical Kinetics jee main questions FREE

Q 1 :

The number of incorrect statement/s from the following is ______. [2023]

A. The successive half-lives of zero-order reactions decrease with time.

B. A substance appearing as reactant in the chemical equation may not affect the rate of reaction.

C. Order and molecularity of a chemical reaction can be a fractional number.

D. The rate constant units of zero and second order reaction are mol $L^{- 1} s^{- 1}$ and ${mol}^{- 1}$ L $s^{- 1}$ respectively.

(1)

(A) For zero order, $t_{1 / 2} = \frac{[A_{0}]}{2 K},$ as time decreases, concentration decreases and hence, half-life decreases. (correct)

(B) If order w.r.t. that reactant is zero, then it will not affect the rate of reaction. (correct)

(C) Order can be fractional but molecularity cannot be. (Incorrect)

(D) Unit of $K = {(mol)}^{1 - n} L t^{n - 1} s^{- 1}$

$n = 0,$ $K = mol L^{- 1} s^{- 1};$ $n = 2$ , $K = {mol}^{- 1} Lt s^{- 1} .$ (correct)

Q 2 :

An organic compound undergoes first order decomposition. The time taken for decomposition to ${((\frac{1}{8}))}^{th}$ and ${((\frac{1}{10}))}^{th}$ of its initial concentration are $t_{1 / 8}$ and $t_{1 / 10}$ respectively.

What is the value of $\frac{t_{1 / 8}}{t_{1 / 10}} \times 10 ?$

$(\log 2 = 0.3)$ [2026]

9
0.9
3
30

1

2

3

4

(1)

$t = \frac{1}{k} \ln \frac{A_{0}}{A_{t}}$

$t_{1 / 8} = \frac{1}{k} \ln \frac{A_{0}}{A_{0} / 8} = \frac{1}{k} \ln 8$

$t_{1 / 10} = \frac{1}{k} \ln \frac{A_{0}}{A_{0} / 10} = \frac{1}{k} \ln 10$

$\frac{t_{1 / 8}}{t_{1 / 10}} = \frac{\ln 8}{\ln 10} = \frac{\log 8}{\log 10}$

$\frac{t_{1 / 8}}{t_{1 / 10}} = \log 8 = 3 \log 2 = 0.9$

$\frac{t_{1 / 8}}{t_{1 / 10}} \times 10 = 9$

Q 3 :

The rate constant value for the decay of radioactive isotopes $X$ and $Y$ , used in radiomedicine are $0.05 h r^{- 1}$ and $0.025 h r^{- 1}$ respectively. In a hospital at a time $' t_{0}'$ , the activity of sample $X$ was found to be twice that of $Y$ . (Activity = no. of disintegrations / sec). The activities of the two radioisotopes will be approximately equal when the time elapsed is ____ hour (Round off to nearest integer). (use ln 2 = 0.7)

(28)

Q 4 :

$t_{99.9}$ is the time required for the reaction to undergo 99.9% completion and $t_{50}$ is the time required for the reaction to undergo 50% completion. The relation between $t_{99.9}$ and $t_{50}$ for a first order reaction is $t_{99.9} = x t_{50}$ . The value of $x$ is _______ (nearest integer).

(10)

$t_{99.9} = \frac{2.303}{K} \log \frac{100}{0.1} = \frac{6.909}{K} = \frac{\frac{6.909}{0.69}}{t_{1 / 2}} = 10 t_{1 / 2}$

Q 5 :

The rate constant for the forward reaction $A (g) \to 2 B (g)$ is $1.5 \times 10^{- 3} s^{- 1}$ at $100 K$ . If $10^{- 5}$ moles of A and 100 moles of B are present in a 10 litre vessel at equilibrium, then the rate constant for the backward reaction at this temperature is

$1.50 \times 10^{4} L m o l^{- 1} s^{- 1}$
$1.5 \times 10^{11} L m o l^{- 1} s^{- 1}$
$1.5 \times 10^{10} L m o l^{- 1} s^{- 1}$
$1.5 \times 10^{- 11} L m o l^{- 1} s^{- 1}$

1

2

3

4

(4)

$A ⇌ 2 B K_{c} = \frac{{[B]}^{2}}{[A]}$

$\frac{K_{f}}{K_{b}} = \frac{{(\frac{100}{10})}^{2}}{(\frac{10^{- 5}}{10})} \Rightarrow \frac{1.5 \times 10^{- 3}}{K_{b}} = \frac{100}{(10^{- 6})} \Rightarrow K_{b} = 1.5 \times 10^{- 11}$

Topic Question Set

(28)

Q 5 :

The rate constant for the forward reaction $A (g) \to 2 B (g)$ is $1.5 \times 10^{- 3} s^{- 1}$ at $100 K$ . If $10^{- 5}$ moles of A and 100 moles of B are present in a 10 litre vessel at equilibrium, then the rate constant for the backward reaction at this temperature is

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Topic Question Set

Q 2 : An organic compound undergoes first order decomposition. The time taken for decomposition to (18)th and (110)th of its initial concentration are t1/8 and t1/10 respectively. What is the value of t1/8t1/10×10 ? (log2=0.3) [2026]

(28)

Q 4 : t99.9 is the time required for the reaction to undergo 99.9% completion and t50 is the time required for the reaction to undergo 50% completion. The relation between t99.9 and t50 for a first order reaction is t99.9=xt50. The value of x is _______ (nearest integer).

Q 5 : The rate constant for the forward reaction A(g)→2B(g) is 1.5×10-3 s-1 at 100 K. If 10-5 moles of A and 100 moles of B are present in a 10 litre vessel at equilibrium, then the rate constant for the backward reaction at this temperature is

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Q 5 :

The rate constant for the forward reaction $A (g) \to 2 B (g)$ is $1.5 \times 10^{- 3} s^{- 1}$ at $100 K$ . If $10^{- 5}$ moles of A and 100 moles of B are present in a 10 litre vessel at equilibrium, then the rate constant for the backward reaction at this temperature is