Question

Thermal decomposition of a compound is of first order . If 50% of a sample of compound is decomposed in 120 minutes, how long will it take for 90% of compound to decompose ?

• A. 299 min
• B. 399 min
• C. 99 min
• D. 9.9 min

Answer 1

The correct option is B 399 min

$k=\frac{0.693}{t_{\frac{1}{2}}}=\frac{0.693}{120}=5.77\times {10}^{-3}mi{n}^{-1}$
$\therefore t=\frac{2.303}{k}log\frac{100}{10}=399min$