Question

The rate constant for a first order reaction is $2.303\times {10}^{–2}{s}^{–1}$. The time required to reduce $8.0\text{g}$ of the reactant to $1.0\text{g}$ is

• A. $60s$
• B. $90s$
• C. $120s$
• D. $150s$

Answer 1

The correct option is B $90s$

$8g\underset{t_{1/2}}{\overset{}{\to }}4g\underset{t_{1/2}}{\overset{}{\to }}2g\underset{t_{1/2}}{\overset{}{\to }}1g$
$\therefore t=3t_{1/2}$
$t=3\times \frac{0.693}{2.303\times {10}^{-2}}=90s$