MCQ
A first order reaction was started with a decimolar solution of the reactant, 8 minutes and 20 seconds later its concentration was found to be $M/100$. So the rate of the reaction is
  • A
    $2.303 \times {10^{ - 5}}\;{\sec ^{ - 1}}$
  • B
    $2.303 \times {10^{ - 4}}\;{\sec ^{ - 1}}$
  • $4.606 \times {10^{ - 3}}\;{\sec ^{ - 1}}$
  • D
    $2.606 \times {10^{ - 5}}\;{\sec ^{ - 1}}$

Answer

Correct option: C.
$4.606 \times {10^{ - 3}}\;{\sec ^{ - 1}}$
c
For first order reaction

$K = \frac{{2.303}}{t}\log \frac{a}{{a - x}}$

Given:

$a = \frac{1}{{10}} = .1\,m$;

$a - x = \frac{1}{{100}} = .01\,m$;

$ t = 500 $ $\sec$

$\therefore \;\;K = \frac{{2.303}}{{500}}\log \frac{{.10}}{{.01}} = \frac{{2.303}}{{500}}\log \,10$

$ = \frac{{2.303}}{{500}} = 0.004606 = 4.6 \times {10^{ - 3}}\,{\sec ^{ - 1}}$.

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