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For the decomposition of azoisopropane to hexane and nitrogen at 543K, the following data are obtained.

            

          Calculate the rate constant.

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Decomposition is represented by the equation-

\left(\mathrm{CH}_3\right)_2 \mathrm{CHN}=\mathrm{NCH}\left(\mathrm{CH}_3\right)_{2(\mathrm{~g})} \longrightarrow \mathrm{N}_{2(\mathrm{~g})}+\mathrm{C}_6 \mathrm{H}_{14(\mathrm{~g})}

\begin{tabular}{lccc} At $t=0$ & $\mathrm{P}_0$ & 0 & 0 \\ At $t=t$ & $\mathrm{P}_0-p$ & $p$ & $p$ \end{tabular}


After t time, the total pressure p_T=p_0-p+(p+p)=p_0+p

                                               So, p=p_t-p_0

thus, p_0-p=2 p_0-p_t

for first order reaction,

\begin{aligned} k & =\frac{2.303}{t} \log \frac{p_0}{p_0-p} \\ & =\frac{2.303}{360} \log \frac{p_0}{2 p_0-p_t}\end{aligned}


now putting the values of pressure,

when t =360sec

\begin{aligned} & =\frac{2.303}{360} \log \frac{35}{2 * 35-54} \\ & =2.175 \times 10^{-3} \mathrm{~s}^{-1}\end{aligned}

when t = 270sec

\begin{aligned} & =\frac{2.303}{270} \log \frac{35}{2 * 35-54} \\ & =2.235 \times 10^{-3} s^{-1}\end{aligned}

So, k_{a v g}=k_1+k_2 / 2
              =2.21 \times 10^{-3} \mathrm{~s}^{-1}

Posted by

manish

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