cases [A] & → & [B] Reactant & & Product cases If formation of...

$\begin{cases}\left[A\right] & \to & \left[B\right] \\ Reactant & & Product\end{cases}$

Since the reaction follows the first order kinetics and after $70$ minutes the concentration of \left[A\right]$was found to be half of its initial concentration. That means 70 minutes is the half life time for the reaction. And we know that for a first order reaction half life time is given as.</p><p>$t\dfrac{1}{2} = \dfrac{0 . 693}{K}K = \dfrac{0 . 693}{{t}_{\dfrac{1}{2}}} = \dfrac{0 . 693}{70 \times 60sec .}$</p><p>$= \dfrac{6930}{7 \times 6} \times {10}^{- 6}\sec^{- 1} = 165 \times {10}^{- 6}\sec^{- 1}So, x = 165