Question

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 of 0.05 mol L${}^{-1}$?

• A. 0.384 min
• B. 0.15 min
• C. 3 min
• D. 3.84 min

Answer 1

Answer: (A)

0.384 min

We know that for first order kinetics:

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

or $t=\frac{2.303}{6}log\frac{0.5}{0.05}=\frac{2.303}{6}=0.384min$

Hence, option A is correct.