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Q. Given gaseous decomposition of A follows first order kinetics. Pure $A(g)$ is taken in a sealed flask where decomposition occurs as,
$A_{\left(\right. g \left.\right)} \rightarrow 2B_{\left(\right. g \left.\right)}+C_{\left(\right. g \left.\right)}$
a leak was developed in the flask, after $10$ sec the leaking gaseous mixture obeys Graham's law. On analysis of the effused gaseous mixture coming out initially, moles of $B(g)$ were found to be double of A. Calculate rate constant in $s e c^{- 1}$ .
Given that Molecular weight of $A=16$
Molecular weight of $ B=4$
Molecular weight of $C=8 $
$ \left[\right.\ln 3=1.1;\ln 2=0.7\left]\right.$
Write your answer by multiplying rate constant with $100$.

NTA AbhyasNTA Abhyas 2022

Solution:

$r_{A}:r_{B}:r_{C}$
$=\frac{P_{A}}{\sqrt{M_{A}}}:\frac{P_{B}}{\sqrt{M_{B}}}:\frac{P_{C}}{\sqrt{M_{C}}}=\frac{P_{0} - P}{4}:\frac{2 P}{2}:\frac{P}{2 \sqrt{2}}$
Also $\frac{P_{0} - P}{4 P}=\frac{1}{2}$
$P_{0}=3Pk=\frac{2 . 303 log \left(3/2\right)}{10}=0.0405\,\sec^{- 1}$
$0.0405\times 100=4$