Question

A first order reaction has a specific reaction rate of ${10}^{-3}{s}^{-1}$. How much time will it takes for $10gm$ of the reactant to reduce to $2.5gm$?

Answer 1

$k=\frac{2.303}{t}log\frac{\left[A_0\right]}{\left[A_t\right]}$
$t=\frac{2.303}{{10}^{-3}}log\frac{10}{2.5}$
$t=2303\times 0.301\times 2=1386s$.