JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    Calculate the rate constant of first order reaction\[C{{H}_{3}}CHO(g)\xrightarrow{Heat}C{{H}_{4}}(g)+CO(g);\] if the initial pressure of \[C{{H}_{3}}CHO\] is 80 mm Hg and the total pressure at the end of 20 minutes is 120 mm Hg.

    A)  \[3.465\times {{10}^{-2}}\,{{\min }^{-1}}\]          

    B)  \[34.65\,{{\min }^{-1}}\]

    C)  \[3.465\,{{\min }^{-1}}\]                             

    D)  \[0.3465\,{{\min }^{-1}}\]

    Correct Answer: A

    Solution :

     \[C{{H}_{3}}CHO(g)\to C{{H}_{4}}(g)+CO(g)\]      \[\begin{matrix}    \text{Initial} & 80\,mm\,Hg & 0 & {}  \\    \text{Final} & 80-p & p & {}  \\ \end{matrix}\begin{matrix}    {} & 0  \\    {} & p  \\ \end{matrix}\] After 20 min. \[80+p=120\] \[\Rightarrow \]               \[p=40\,mm\,Hg\] i.e. 50% of reaction is complete. i.e., \[{{t}_{1/2}}\]= 20 min \[\therefore \] \[k=\frac{0.693}{{{t}_{1/2}}}=\frac{0.693}{20}=3.465\times {{10}^{-2}}{{\min }^{-1}}\]


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