• # question_answer A reaction that is of the first order with respect to reactant A has a rate constant $6{{\min }^{-1}}$. If we start with [A]$0.5\,mol\,{{l}^{-1}},$ when would [A] reach the value $0.05\,mol\,{{l}^{-1}}$ A) 0.384 min B) 0.15 min C) 3 min                D) 3.84 min

 We know that for first order kinetics $k=\frac{2.303}{t}\log \frac{a}{a-x},\left( a-x \right)=0.05mol\text{ }{{l}^{-1}}$ $6=\frac{2.3030}{t}\log \frac{0.5}{0.05}$ or  $t=\frac{2.303}{6}\log \frac{0.5}{0.05}=\frac{2.303}{6}=0.384\text{ }\min$