Question

$t_{1/2}$ for a first order reaction is $14.26min$. Calculate the time when $5\%$ of the reactant is left.

• A. $62min$
• B. $42min$
• C. $26min$
• D. $53min$

Answer 1

Answer: (A)

$x=100\%-5\%=95\%$
$k=\frac{0.693}{t_{1/2}}=\frac{0.693}{14.26}=0.0486$
$k=\frac{2.303}{t}log\frac{a}{a-x}$
$t=\frac{2.303}{0.0486}log\frac{100}{100-95}$
$t=61.65min\approx 62min$