# If a reactant is used up according to a first order rate equation and initial concentration of reactant is $32mol\;L^{-1}$ what is concentration of reactant after six half lives have passed?

$\begin{array}{1 1}(a)\;0.8&(b)\;0.1\\(c)\;0.05&(d)\;0.01\end{array}$

After half life reactant halts so after n half life it becomes $\large\frac{a}{2^n}$ where $a$ is initial concentration.
So $\large\frac{a}{2^6}=\frac{3.2}{64}$
$\Rightarrow 0.05M$
edited Jul 27, 2014