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JEE Advanced · Chemistry · 18. Chemical Kinetics

For the first order reaction \(2 \mathrm{~N}_2 \mathrm{O}_5(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}_2(g)+\mathrm{O}_2(g)\)

  1. A the concentration of the reactant decreases exponentially with time.
  2. B the half-life of the reaction decreases with increasing temperature
  3. C the half-life of the reaction depends on the initial concentration of the reactant.
  4. D the reaction proceeds of \(99.6 \%\) completion in eight half-life duration.
Verified Solution

Answer & Solution

Correct Answer

(A) the concentration of the reactant decreases exponentially with time.

Step-by-step Solution

Detailed explanation

(a) For a first order reaction, the concentration of reactant remaining after time \(t\) is given by \([A]=[A]_0 e^{-k t}\) Therefore, concentration of reactant decreases exponentially with time.
(b) Rise in temperature increases rate constant \((k)\) and therefore decreases half-life \(\left(t_{1 / 2}\right)\) as
\(
t_{1 / 2}=\frac{\operatorname{In} 2}{k}
\)

(d) For a first order reaction, if 100 moles of reactant is taken initially, after \(n\) half-lives, reactant remaining is given by
\(\text {Percentage } A=100\left(\frac{1}{2}\right)^n=100\left(\frac{1}{2}\right)^8=0.3906 \)
\( \Rightarrow \text {A reacted }=100-0.3906=99.6 \%\)
(c) Half-life of first order reaction is independent of initial concentration.
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